-\input texinfo @c -*-texinfo-*-
+\input texinfo
@c %**start of header
@setfilename tar.info
-@settitle The Tar Manual: DRAFT
-@setchapternewpage odd
+@settitle GNU tar
+@finalout
+@smallbook
@c %**end of header
-@c Note: the edition number and date is listed in *two* places; please update.
-@c subtitle and top node; search for !!set
-
-@c Search for comments marked with !! or <<< (or >>>)
-
-@c <<< CONVENTIONS: this manual refers to "ordinary files" , "directory
-files" (or "directories"), "archive files", "archive members", and
-various I/O devices (which have names and file names).>>>
+@c ======================================================================
+@c This document has three levels of rendition: PUBLISH, DISTRIB or PROOF,
+@c as decided by @set symbols. The PUBLISH rendition does not show
+@c notes or marks asking for revision. Most users will prefer having more
+@c information, even if this information is not fully revised for adequacy,
+@c so DISTRIB is the default for tar distributions. The PROOF rendition
+@c show all marks to the point of ugliness, but is nevertheless useful to
+@c those working on the manual itself.
+@c ======================================================================
+
+@ifclear PUBLISH
+@ifclear DISTRIB
+@ifclear PROOF
+@set DISTRIB
+@end ifclear
+@end ifclear
+@end ifclear
+
+@ifset PUBLISH
+@set RENDITION The book, version
+@end ifset
+
+@ifset DISTRIB
+@set RENDITION FTP release, version
+@end ifset
+
+@ifset PROOF
+@set RENDITION Proof reading version
+@end ifset
+
+@c ---------------------------------------------------------------------
+@c The @FIXME's, @UNREVISED and @c comments are part Fran@,{c}ois's work
+@c plan. These annotations are somewhat precious to him; he asks that I
+@c do not alter them inconsiderately. Much work is needed for GNU tar
+@c internals (the sources, the programs themselves). Revising the
+@c adequacy of the manual while revising the sources, and cleaning them
+@c both at the same time, seems to him like a good way to proceed.
+@c ---------------------------------------------------------------------
+
+@c Output marks for nodes needing revision, but not in PUBLISH rendition.
+
+@macro UNREVISED
+@ifclear PUBLISH
+@quotation
+@emph{(This message will disappear, once this node revised.)}
+@end quotation
+@end ifclear
+@end macro
+
+@c Output various FIXME information only in PROOF rendition.
+
+@macro FIXME{string}
+@allow-recursion
+@quote-arg
+@ifset PROOF
+@strong{<FIXME>} \string\ @strong{</>}
+@end ifset
+
+@end macro
+
+@macro FIXME-ref{string}
+@quote-arg
+@ifset PROOF
+@strong{<REF>} \string\ @strong{</>}
+@end ifset
+
+@end macro
+
+@macro FIXME-pxref{string}
+@quote-arg
+@ifset PROOF
+@strong{<PXREF>} \string\ @strong{</>}
+@end ifset
+
+@end macro
+
+@macro FIXME-xref{string}
+@quote-arg
+@ifset PROOF
+@strong{<XREF>} \string\ @strong{</>}
+@end ifset
+
+@end macro
+
+@c @macro option{entry}
+@c @quote-arg
+@c @opindex{--\entry\}
+@c @value{\entry\}
+@c @end macro
+
+@set op-absolute-names @kbd{--absolute-names} (@kbd{-P})
+@set ref-absolute-names @ref{absolute}
+@set xref-absolute-names @xref{absolute}
+@set pxref-absolute-names @pxref{absolute}
+
+@set op-after-date @kbd{--after-date=@var{date}} (@kbd{--newer=@var{date}}, @kbd{-N @var{date}})
+@set ref-after-date @ref{after}
+@set xref-after-date @xref{after}
+@set pxref-after-date @pxref{after}
+
+@set op-append @kbd{--append} (@kbd{-r})
+@set ref-append @ref{add}
+@set xref-append @xref{add}
+@set pxref-append @pxref{add}
+
+@set op-atime-preserve @kbd{--atime-preserve}
+@set ref-atime-preserve @ref{Attributes}
+@set xref-atime-preserve @xref{Attributes}
+@set pxref-atime-preserve @pxref{Attributes}
+
+@set op-backup @kbd{--backup}
+@set ref-backup @ref{Backup options}
+@set xref-backup @xref{Backup options}
+@set pxref-backup @pxref{Backup options}
+
+@set op-block-number @kbd{--block-number} (@kbd{-R})
+@set ref-block-number @ref{verbose}
+@set xref-block-number @xref{verbose}
+@set pxref-block-number @pxref{verbose}
+
+@set op-blocking-factor @kbd{--blocking-factor=@var{512-size}} (@kbd{-b @var{512-size}})
+@set ref-blocking-factor @ref{Blocking Factor}
+@set xref-blocking-factor @xref{Blocking Factor}
+@set pxref-blocking-factor @pxref{Blocking Factor}
+
+@set op-checkpoint @kbd{--checkpoint}
+@set ref-checkpoint @ref{verbose}
+@set xref-checkpoint @xref{verbose}
+@set pxref-checkpoint @pxref{verbose}
+
+@set op-compare @kbd{--compare} (@kbd{--diff}, @kbd{-d})
+@set ref-compare @ref{compare}
+@set xref-compare @xref{compare}
+@set pxref-compare @pxref{compare}
+
+@set op-compress @kbd{--compress} (@kbd{--uncompress}, @kbd{-Z})
+@set ref-compress @ref{gzip}
+@set xref-compress @xref{gzip}
+@set pxref-compress @pxref{gzip}
+
+@set op-concatenate @kbd{--concatenate} (@kbd{--catenate}, @kbd{-A})
+@set ref-concatenate @ref{concatenate}
+@set xref-concatenate @xref{concatenate}
+@set pxref-concatenate @pxref{concatenate}
+
+@set op-create @kbd{--create} (@kbd{-c})
+@set ref-create @ref{create}
+@set xref-create @xref{create}
+@set pxref-create @pxref{create}
+
+@set op-delete @kbd{--delete}
+@set ref-delete @ref{delete}
+@set xref-delete @xref{delete}
+@set pxref-delete @pxref{delete}
+
+@set op-dereference @kbd{--dereference} (@kbd{-h})
+@set ref-dereference @ref{dereference}
+@set xref-dereference @xref{dereference}
+@set pxref-dereference @pxref{dereference}
+
+@set op-directory @kbd{--directory=@var{directory}} (@kbd{-C @var{directory}})
+@set ref-directory @ref{directory}
+@set xref-directory @xref{directory}
+@set pxref-directory @pxref{directory}
+
+@set op-exclude @kbd{--exclude=@var{pattern}}
+@set ref-exclude @ref{exclude}
+@set xref-exclude @xref{exclude}
+@set pxref-exclude @pxref{exclude}
+
+@set op-exclude-from @kbd{--exclude-from=@var{file-of-patterns}} (@kbd{-X @var{file-of-patterns}})
+@set ref-exclude-from @ref{exclude}
+@set xref-exclude-from @xref{exclude}
+@set pxref-exclude-from @pxref{exclude}
+
+@set op-extract @kbd{--extract} (@kbd{--get}, @kbd{-x})
+@set ref-extract @ref{extract}
+@set xref-extract @xref{extract}
+@set pxref-extract @pxref{extract}
+
+@set op-file @kbd{--file=@var{archive-name}} (@kbd{-f @var{archive-name}})
+@set ref-file @ref{file}
+@set xref-file @xref{file}
+@set pxref-file @pxref{file}
+
+@set op-files-from @kbd{--files-from=@var{file-of-names}} (@kbd{-T @var{file-of-names}})
+@set ref-files-from @ref{files}
+@set xref-files-from @xref{files}
+@set pxref-files-from @pxref{files}
+
+@set op-force-local @kbd{--force-local}
+@set ref-force-local @ref{file}
+@set xref-force-local @xref{file}
+@set pxref-force-local @pxref{file}
+
+@set op-group @kbd{--group=@var{group}}
+@set ref-group @ref{Option Summary}
+@set xref-group @xref{Option Summary}
+@set pxref-group @pxref{Option Summary}
+
+@set op-gzip @kbd{--gzip} (@kbd{--gunzip}, @kbd{--ungzip}, @kbd{-z})
+@set ref-gzip @ref{gzip}
+@set xref-gzip @xref{gzip}
+@set pxref-gzip @pxref{gzip}
+
+@set op-help @kbd{--help}
+@set ref-help @ref{help}
+@set xref-help @xref{help}
+@set pxref-help @pxref{help}
+
+@set op-ignore-failed-read @kbd{--ignore-failed-read}
+@set ref-ignore-failed-read @ref{Reading}
+@set xref-ignore-failed-read @xref{Reading}
+@set pxref-ignore-failed-read @pxref{Reading}
+
+@set op-ignore-zeros @kbd{--ignore-zeros} (@kbd{-i})
+@set ref-ignore-zeros @ref{Reading}
+@set xref-ignore-zeros @xref{Reading}
+@set pxref-ignore-zeros @pxref{Reading}
+
+@set op-incremental @kbd{--incremental} (@kbd{-G})
+@set ref-incremental @ref{Inc Dumps}
+@set xref-incremental @xref{Inc Dumps}
+@set pxref-incremental @pxref{Inc Dumps}
+
+@set op-info-script @kbd{--info-script=@var{script-name}} (@kbd{--new-volume-script=@var{script-name}}, @kbd{-F @var{script-name}})
+@set ref-info-script @ref{Multi-Volume Archives}
+@set xref-info-script @xref{Multi-Volume Archives}
+@set pxref-info-script @pxref{Multi-Volume Archives}
+
+@set op-interactive @kbd{--interactive} (@kbd{-w})
+@set ref-interactive @ref{interactive}
+@set xref-interactive @xref{interactive}
+@set pxref-interactive @pxref{interactive}
+
+@set op-keep-old-files @kbd{--keep-old-files} (@kbd{-k})
+@set ref-keep-old-files @ref{Writing}
+@set xref-keep-old-files @xref{Writing}
+@set pxref-keep-old-files @pxref{Writing}
+
+@set op-label @kbd{--label=@var{archive-label}} (@kbd{-V @var{archive-label}})
+@set ref-label @ref{label}
+@set xref-label @xref{label}
+@set pxref-label @pxref{label}
+
+@set op-list @kbd{--list} (@kbd{-t})
+@set ref-list @ref{list}
+@set xref-list @xref{list}
+@set pxref-list @pxref{list}
+
+@set op-listed-incremental @kbd{--listed-incremental=@var{snapshot-file}} (@kbd{-g @var{snapshot-file}})
+@set ref-listed-incremental @ref{Inc Dumps}
+@set xref-listed-incremental @xref{Inc Dumps}
+@set pxref-listed-incremental @pxref{Inc Dumps}
+
+@set op-mode @kbd{--mode=@var{permissions}}
+@set ref-mode @ref{Option Summary}
+@set xref-mode @xref{Option Summary}
+@set pxref-mode @pxref{Option Summary}
+
+@set op-multi-volume @kbd{--multi-volume} (@kbd{-M})
+@set ref-multi-volume @ref{Multi-Volume Archives}
+@set xref-multi-volume @xref{Multi-Volume Archives}
+@set pxref-multi-volume @pxref{Multi-Volume Archives}
+
+@set op-newer-mtime @kbd{--newer-mtime=@var{date}}
+@set ref-newer-mtime @ref{after}
+@set xref-newer-mtime @xref{after}
+@set pxref-newer-mtime @pxref{after}
+
+@set op-no-recursion @kbd{--no-recursion}
+@set ref-no-recursion @ref{recurse}
+@set xref-no-recursion @xref{recurse}
+@set pxref-no-recursion @pxref{recurse}
+
+@set op-null @kbd{--null}
+@set ref-null @ref{files}
+@set xref-null @xref{files}
+@set pxref-null @pxref{files}
+
+@set op-numeric-owner @kbd{--numeric-owner}
+@set ref-numeric-owner @ref{Attributes}
+@set xref-numeric-owner @xref{Attributes}
+@set pxref-numeric-owner @pxref{Attributes}
+
+@set op-old-archive @kbd{--old-archive} (@kbd{-o})
+@set ref-old-archive @ref{old}
+@set xref-old-archive @xref{old}
+@set pxref-old-archive @pxref{old}
+
+@set op-one-file-system @kbd{--one-file-system} (@kbd{-l})
+@set ref-one-file-system @ref{one}
+@set xref-one-file-system @xref{one}
+@set pxref-one-file-system @pxref{one}
+
+@set op-owner @kbd{--owner=@var{user}}
+@set ref-owner @ref{Option Summary}
+@set xref-owner @xref{Option Summary}
+@set pxref-owner @pxref{Option Summary}
+
+@set op-posix @kbd{--posix}
+@set ref-posix @ref{posix}
+@set xref-posix @xref{posix}
+@set pxref-posix @pxref{posix}
+
+@set op-preserve @kbd{--preserve}
+@set ref-preserve @ref{Attributes}
+@set xref-preserve @xref{Attributes}
+@set pxref-preserve @pxref{Attributes}
+
+@set op-record-size @kbd{--record-size=@var{size}}
+@set ref-record-size @ref{Blocking}
+@set xref-record-size @xref{Blocking}
+@set pxref-record-size @pxref{Blocking}
+
+@set op-recursive-unlink @kbd{--recursive-unlink}
+@set ref-recursive-unlink @ref{Writing}
+@set xref-recursive-unlink @xref{Writing}
+@set pxref-recursive-unlink @pxref{Writing}
+
+@set op-read-full-records @kbd{--read-full-records} (@kbd{-B})
+@set ref-read-full-records @ref{Blocking}
+@set xref-read-full-records @xref{Blocking}
+@set pxref-read-full-records @pxref{Blocking}
+@c FIXME: or should it be Reading, or Blocking Factor
+
+@set op-remove-files @kbd{--remove-files}
+@set ref-remove-files @ref{Writing}
+@set xref-remove-files @xref{Writing}
+@set pxref-remove-files @pxref{Writing}
+
+@set op-rsh-command @kbd{rsh-command=@var{command}}
+
+@set op-same-order @kbd{--same-order} (@kbd{--preserve-order}, @kbd{-s})
+@set ref-same-order @ref{Scarce}
+@set xref-same-order @xref{Scarce}
+@set pxref-same-order @pxref{Scarce}
+@c FIXME: or should it be Reading, or Attributes?
+
+@set op-same-owner @kbd{--same-owner}
+@set ref-same-owner @ref{Attributes}
+@set xref-same-owner @xref{Attributes}
+@set pxref-same-owner @pxref{Attributes}
+
+@set op-same-permissions @kbd{--same-permissions} (@kbd{--preserve-permissions}, @kbd{-p})
+@set ref-same-permissions @ref{Attributes}
+@set xref-same-permissions @xref{Attributes}
+@set pxref-same-permissions @pxref{Attributes}
+@c FIXME: or should it be Writing?
+
+@set op-show-omitted-dirs @kbd{--show-omitted-dirs}
+@set ref-show-omitted-dirs @ref{verbose}
+@set xref-show-omitted-dirs @xref{verbose}
+@set pxref-show-omitted-dirs @pxref{verbose}
+
+@set op-sparse @kbd{--sparse} (@kbd{-S})
+@set ref-sparse @ref{sparse}
+@set xref-sparse @xref{sparse}
+@set pxref-sparse @pxref{sparse}
+
+@set op-starting-file @kbd{--starting-file=@var{name}} (@kbd{-K @var{name}})
+@set ref-starting-file @ref{Scarce}
+@set xref-starting-file @xref{Scarce}
+@set pxref-starting-file @pxref{Scarce}
+
+@set op-suffix @kbd{--suffix=@var{suffix}}
+@set ref-suffix @ref{Backup options}
+@set xref-suffix @xref{Backup options}
+@set pxref-suffix @pxref{Backup options}
+
+@set op-tape-length @kbd{--tape-length=@var{1024-size}} (@kbd{-L @var{1024-size}})
+@set ref-tape-length @ref{Using Multiple Tapes}
+@set xref-tape-length @xref{Using Multiple Tapes}
+@set pxref-tape-length @pxref{Using Multiple Tapes}
+
+@set op-to-stdout @kbd{--to-stdout} (@kbd{-O})
+@set ref-to-stdout @ref{Writing}
+@set xref-to-stdout @xref{Writing}
+@set pxref-to-stdout @pxref{Writing}
+
+@set op-totals @kbd{--totals}
+@set ref-totals @ref{verbose}
+@set xref-totals @xref{verbose}
+@set pxref-totals @pxref{verbose}
+
+@set op-touch @kbd{--touch} (@kbd{-m})
+@set ref-touch @ref{Writing}
+@set xref-touch @xref{Writing}
+@set pxref-touch @pxref{Writing}
+
+@set op-unlink-first @kbd{--unlink-first} (@kbd{-U})
+@set ref-unlink-first @ref{Writing}
+@set xref-unlink-first @xref{Writing}
+@set pxref-unlink-first @pxref{Writing}
+
+@set op-update @kbd{--update} (@kbd{-u})
+@set ref-update @ref{update}
+@set xref-update @xref{update}
+@set pxref-update @pxref{update}
+
+@set op-use-compress-prog @kbd{--use-compress-prog=@var{program}}
+@set ref-use-compress-prog @ref{gzip}
+@set xref-use-compress-prog @xref{gzip}
+@set pxref-use-compress-prog @pxref{gzip}
+
+@set op-verbose @kbd{--verbose} (@kbd{-v})
+@set ref-verbose @ref{verbose}
+@set xref-verbose @xref{verbose}
+@set pxref-verbose @pxref{verbose}
+
+@set op-verify @kbd{--verify} (@kbd{-W})
+@set ref-verify @ref{verify}
+@set xref-verify @xref{verify}
+@set pxref-verify @pxref{verify}
+
+@set op-version @kbd{--version}
+@set ref-version @ref{help}
+@set xref-version @xref{help}
+@set pxref-version @pxref{help}
+
+@set op-version-control @kbd{--version-control=@var{method}}
+@set ref-version-control @ref{Backup options}
+@set xref-version-control @xref{Backup options}
+@set pxref-version-control @pxref{Backup options}
+
+@set op-volno-file @kbd{--volno-file=@var{file-of-number}}
+@set ref-volno-file @ref{Using Multiple Tapes}
+@set xref-volno-file @xref{Using Multiple Tapes}
+@set pxref-volno-file @pxref{Using Multiple Tapes}
+
+@include version.texi
+
+@c Put everything in one index (arbitrarily chosen to be the concept index).
+@syncodeindex fn cp
+@syncodeindex ky cp
+@syncodeindex pg cp
+@syncodeindex vr cp
+
+@defindex op
+@syncodeindex op cp
-@c <<< it's "file name" (not filename) unless we are talking about an
-argument, ie. @var{file-name}. also, you "use" a "file-name argument"
-to "specify" a "file".>>>
+@ifinfo
+@format
+START-INFO-DIR-ENTRY
+* tar: (tar). Making tape (or disk) archives.
+END-INFO-DIR-ENTRY
+@end format
+@end ifinfo
-@c <<< @code{tar} is always lower case, in bold. >>>
+@ifinfo
+This file documents GNU @code{tar}, a utility used to store, backup, and
+transport files.
-@c <<< it's "operations of tar", "options to tar" also, it's " @samp{tar
-+foo}" or "the @samp{+foo} operation". MIB doesn't like using
-operations and options as separate concepts. I disagree --- would be a
-mess to explain otherwise
+Copyright (C) 1992, 1994, 1995, 1996, 1997, 1999 Free Software Foundation, Inc.
-@c <<< (don't forget to comment these out in final draft) -ringo
+Permission is granted to make and distribute verbatim copies of
+this manual provided the copyright notice and this permission notice
+are preserved on all copies.
-@c <<< please dont' change this without sending me e-mail. some things
-@c are in progress or waiting to be edited in hardcopy. -ringo
-@c smallbook
+@ignore
+Permission is granted to process this file through TeX and print the
+results, provided the printed document carries copying permission
+notice identical to this one except for the removal of this paragraph
+(this paragraph not being relevant to the printed manual).
-@iftex
-@c finalout
-@end iftex
+@end ignore
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided that the entire
+resulting derived work is distributed under the terms of a permission
+notice identical to this one.
+
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation approved
+by the Foundation.
+@end ifinfo
-@ifinfo
-This file documents @code{tar}, a utility used to store, backup, and
-transport files.
+@setchapternewpage odd
-Copyright (C) 1992 Free Software Foundation, Inc. DRAFT!
-@c Need to put distribution information here when ready.
-@end ifinfo
+@shorttitlepage GNU @code{tar}
-@c !!set edition number and date here
@titlepage
-@title @code{tar}
-@subtitle The GNU Tape Archiver
-@subtitle Edition 0.01, for @code{tar} Version 1.10
-@subtitle @today{}
-@c remove preceding today line when ready
-@sp 1
-@subtitle DRAFT
-@c subtitle insert month here when ready
-
-@author Amy Gorin and Jay Fenlason
-@c <<<best to have hack read this over and see if anything is left he
-@c wrote. I don't think so. -ringo>>>>
+@title GNU tar: an archiver tool
+@subtitle @value{RENDITION} @value{VERSION}, @value{UPDATED}
+@author Melissa Weisshaus, Jay Fenlason,
+@author Thomas Bushnell, n/BSG, Amy Gorin
+@c he said to remove it: Fran@,{c}ois Pinard
+@c i'm thinking about how the author page *should* look. -mew 2may96
@page
@vskip 0pt plus 1filll
-Copyright @copyright{} 1992 Free Software Foundation, Inc.
-
-@sp 2
-This draft is not yet ready for distribution.
+Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999 Free Software
+Foundation, Inc.
+
+Permission is granted to make and distribute verbatim copies of
+this manual provided the copyright notice and this permission notice
+are preserved on all copies.
+
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided that the entire
+resulting derived work is distributed under the terms of a permission
+notice identical to this one.
+
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation approved
+by the Foundation.
@end titlepage
@ifinfo
-@node Top, Introduction, (dir), (dir)
-@top @code{tar}
-This file documents @code{tar}, a utility used to store, backup, and
-transport files.
+This file documents GNU @code{tar}, which is a utility used to store,
+backup, and transport files. @code{tar} is a tape (or disk) archiver.
+This manual documents the release @value{VERSION}.
-@c !!set edition number and date here
-This is DRAFT Edition 0.01 of the @code{tar} documentation, @today{}, for @code{tar}
-version 1.12.
@end ifinfo
-@c <<< The menus need to be gone over, and node names fixed.
+@node Top, Introduction, (dir), (dir)
+
@menu
-* Introduction:: @code{tar}: The GNU Tape Archiver
-* Invoking @code{tar}:: How to invoke @code{tar}
-* Tutorial:: Getting started
-* Wizardry:: Some More Advanced Uses for @code{tar}
-* Archive Structure:: The structure of an archive
-* Reading and Writing:: Reading and writing archives
-* Insuring Accuracy:: How to insure the accuracy of an archive
-* Selecting Archive Members:: How to select archive members
-* User Interaction:: How @code{tar} interacts with people.
-* Backups and Restoration:: How to restore files and perform backups
-* Media:: Using tapes and other archive media
-* Quick Reference:: A quick reference guide to
- @code{tar} operations and options
-* Data Format Details:: Details of the archive data format
-* Concept Index:: Concept Index
-@end menu
+* Introduction::
+* Tutorial::
+* tar invocation::
+* operations::
+* Backups::
+* Choosing::
+* Date input formats::
+* Formats::
+* Media::
+* Index::
-@node Introduction, Invoking @code{tar}, Top, Top
-@chapter @code{tar}: The GNU Tape Archiver
+ --- The Detailed Node Listing ---
-You can use @code{tar} to create an @dfn{archive}---a single file
-which contains other file's contents as well as a listing of those
-files' characteristics. You can also use @code{tar} to read, add to,
-or manipulate already existing archives. Because an archive created
-by @code{tar} is capable of preserving file information and directory
-structure, @code{tar} is ideal for performing full and incremental
-backups, as well as for transferring groups of files between disks and
-over networks.
+Introduction
-Despite the utility's name, which comes from the words @samp{T(ape)}
-@samp{AR(chiver)}, @code{tar}'s output can be directed to any
-available device. For instance, @code{tar} archives can be stored in
-a file or sent to another program via a pipe.
+* Book Contents:: What this Book Contains
+* Definitions:: Some Definitions
+* What tar Does:: What @code{tar} Does
+* Naming tar Archives:: How @code{tar} Archives are Named
+* posix compliance::
+* Authors:: GNU @code{tar} Authors
+* Reports:: Reporting bugs or suggestions
-@c <<< this menu will conflict with menu above in info mode. -ringo
-@menu
-* Invoking @code{tar}:: How to invoke @code{tar} and specify arguments.
-* Tutorial:: An introduction to @code{tar}.
-* Operations:: What you can use @code{tar} to do.
-* Options:: How to change the way @code{tar} behaves.
-* Problems:: Common problems with @code{tar}.
-@end menu
+Tutorial Introduction to @code{tar}
-@node Invoking @code{tar}, Tutorial, Introduction, Top
-@chapter How To Invoke @code{tar}
+* assumptions::
+* stylistic conventions::
+* basic tar options:: Basic @code{tar} Operations and Options
+* frequent operations::
+* Two Frequent Options::
+* create:: How to Create Archives
+* list:: How to List Archives
+* extract:: How to Extract Members from an Archive
+* going further::
-You can use @code{tar} to store files in an archive, to extract them
-from an archive, and to do other types of archive manipulation. The
-primary argument to @code{tar}, which is called the @dfn{operation},
-specifies which action to take. The other arguments to @code{tar} are
-either @dfn{options}, which change the way @code{tar} performs an
-operation, or @dfn{file-names}, which specify the files @code{tar} is
-to act on. The typical @code{tar} command line syntax is:
+Two Frequently Used Options
-@example
-@code{tar} @var{operation} [@var{options}...] [@var{file-names}...]
-@end example
+* file tutorial::
+* verbose tutorial::
+* help tutorial::
-Note: You can actually type in arguments in any order. In this manual
-the operation is always first, the options second and the file-name
-arguments last, to make examples easier to understand.
+How to Create Archives
-@menu
-* Argument Functions:: The Functions of Arguments
-* Argument Form:: The Forms of Arguments
-* Old Syntax for Commands:: An Old, but Still Supported, Syntax
- for @code{tar} Commands
-@end menu
+* prepare for examples::
+* Creating the archive::
+* create verbose::
+* short create::
+* create dir::
-@node Argument Functions, Argument Form, Invoking @code{tar}, Invoking @code{tar}
-@section The Functions of Arguments
+How to List Archives
-The primary argument to @code{tar} is the @dfn{operation}, which
-specifies what @code{tar} does. @code{tar} can be used to:
+* list dir::
-@itemize
-@item
-Add files to an existing archive (@samp{+add-file}, @samp+{append} or
-@samp{-r})
+How to Extract Members from an Archive
-@item
-Compare files in an archive with files in the file system
-(@samp{+compare}, @samp{+diff} or @samp{-d})
-@c !!! is diff still working?? --- yes -ringo
+* extracting archives::
+* extracting files::
+* extract dir::
+* failing commands::
-@item
-Add archives to another archive (@samp{+add-archive}, @samp{+catenate}
-or @samp{-A})
-@c was +concatenate. -ringo
+Invoking GNU @code{tar}
-@item
-Create an archive (@samp{+create} or @samp{-c})
+* Synopsis::
+* using tar options::
+* Styles::
+* All Options::
+* help::
+* verbose::
+* interactive::
-@item
-Delete files from an archive (@samp{+delete})
-@c -D should have been removed -ringo
+The Three Option Styles
-@item
-Extract files from an archive (@samp{+extract}, @samp{+get} or @samp{-x})
+* Mnemonic Options:: Mnemonic Option Style
+* Short Options:: Short Option Style
+* Old Options:: Old Option Style
+* Mixing:: Mixing Option Styles
-@item
-List the files in an archive (@samp{+list} or @samp{-t})
+All @code{tar} Options
-@item
-Update an archive by appending newer versions of already stored files
-(@samp{+update} or @samp{-u})
-@end itemize
+* Operation Summary::
+* Option Summary::
+* Short Option Summary::
-@xref{Reading and Writing}, for more information about these
-operations.
-
-@dfn{Option} arguments to @code{tar} change details of the operation,
-such as archive format, archive name, or level of user interaction.
-You can specify more than one option. All options are optional.
-
-@dfn{File-name} arguments specify which files (including directory
-files) to archive, extract, delete or otherwise operate on.
-
-If you don't use any file-name arguments, @samp{+add-file},
-@samp{+update} and @samp{+delete} will do nothing. The other
-operations of @code{tar} will act on defaults.
-
-When you use a file-name argument to specify a directory file,
-@code{tar} acts on all the files in that directory, including
-sub-directories.
-
-@node Argument Form, Old Syntax for Commands, Argument Functions, Invoking @code{tar}
-@section The Forms of Arguments
-
-Most operations of @code{tar} have a single letter form (a single
-letter preceded by a @samp{-}), and at least one mnemonic form (a
-word or abbreviation preceded by a @samp{+}). The forms are
-identical in function. For example, you can use either @samp{tar -t}
-or @samp{tar +list} to list the contents of an archive
-
-Options, like operations, have both single letter and mnemonic forms.
-Options, however, may also incorporate an argument. Single letter
-options are separated from their arguments by a space. Mnemonic
-options are separated from their arguments by an @samp{=} sign. For
-example, to create an an archive file named @file{george}, use either
-@samp{tar +create +file=george} or @samp{tar +create -f george}. Both
-@samp{+file=@var{archive-name}} and @samp{-f @var{archive-name}}
-denote the option to give the archive a non-default name, which in the
-example is @samp{george}.
-
-You can mix single letter and mnemonic forms in the same command. You
-could type the above example as @samp{tar -c +file=george} or
-@samp{tar +create -f george}. However, @code{tar} operations and
-options are case sensitive. You would not type the above example as
-@samp{tar -C +file=george}, because @samp{-C} is an option that causes
-@code{tar} to change directories, not an operation that creates an
-archive.
+GNU @code{tar} Operations
-File-name arguments are the names of files (including directories).
-These names can be specified on the command line or read from a text
-file in the file system (using the @samp{+files-from} option). Files
-stored in an archive are called @dfn{archive members}. The operations
-@samp{+delete}, @samp{+extract}, @samp{+list}, @samp{+compare} and
-@samp{+update} take the names of archive members as file-name
-arguments. The other operations take the names of files in the file
-system.
+* Basic tar::
+* Advanced tar::
+* extract options::
+* backup::
+* Applications::
+* looking ahead::
-@code{tar} interprets relative file names as being relative to the
-working directory. @code{tar} will make all file names relative (by
-removing leading @samp{/}s when archiving or restoring files), unless
-you specify otherwise (using the @samp{+absolute-paths} option).
-@xref{File Name Interpretation}, for more information about
-@samp{+absolute-paths}.
-@c >>> yet another node name that is probably wrong.
+Advanced GNU @code{tar} Operations
-@node Old Syntax for Commands, , Argument Form, Invoking @code{tar}
-@section An Old, but Still Supported, Syntax for @code{tar} Commands
+* Operations::
+* current state::
+* append::
+* update::
+* concatenate::
+* delete::
+* compare::
-For historical reasons, GNU @code{tar} also accepts a syntax for
-commands which splits options that include arguments into two parts.
-That syntax is of the form:
+How to Add Files to Existing Archives: @code{--append}
-@example
-@code{tar} @var{operation}[@var{option-letters}...] [@var{option-arguments}...] [@var{file-names}...]@refill
-@end example
+* appending files:: Appending Files to an Archive
+* multiple::
-@noindent
-where arguments to the options appear in the same order as the letters
-to which they correspond, and the operation and all the option letters
-appear as a single argument, without separating spaces.
-
-This command syntax is useful because it lets you type the single
-letter forms of the operation and options as a single argument to
-@code{tar}, without writing preceding @samp{-}s or inserting spaces
-between letters. @samp{tar cv} or @samp{tar -cv} are equivalent to
-@samp{tar -c -v}.
-
-This old style syntax makes it difficult to match option letters with
-their corresponding arguments, and is often confusing. In the command
-@samp{tar cvbf 20 /dev/rmt0}, for example, @samp{20} is the argument
-for @samp{-b}, @samp{/dev/rmt0} is the argument for @samp{-f}, and
-@samp{-v} does not have a corresponding argument. The modern
-syntax---@samp{tar -c -v -b 20 -f /dev/rmt0}---is clearer.
-
-@node Tutorial, Wizardry, Invoking @code{tar}, Top
-@chapter Getting Started With @code{tar}
-
-This chapter guides you through some basic examples of @code{tar}
-operations. In the examples, the lines you should type are preceded
-by a @samp{%}, which is a typical shell prompt. We use mnemonic forms
-of operations and options in the examples, and in discussions in the
-text, but short forms produce the same result.
+Updating an Archive
-@menu
-* Creating Archives:: Creating Archives
-* Extracting Files:: Extracting Files from an Archive
-* Listing Archive Contents:: Listing the Contents of an Archive
-* Comparing Files:: Comparing Archives with the File System
-* Adding to Archives:: Adding Files to Existing Archives
-* Concatenate:: Concatenating Archives
-* Deleting Files:: Deleting Files From an Archive
-@end menu
+* how to update::
-@node Creating Archives, Listing Archive Contents, Tutorial, Tutorial
-@section Creating Archives
+Options Used by @code{--extract}
-To create a new archive, use @code{tar +create} (or @code{tar -c}).
-You can use options to specify the name and format of the archive (as
-well as other characteristics), and you can use file-name arguments to
-specify which files to put in the archive. If you don't use any
-options or file-name arguments, @code{tar} will use default values.
-@xref{Creating Example}, for more information about the @samp{+create}
-operation.
+* Reading:: Options to Help Read Archives
+* Writing:: Changing How @code{tar} Writes Files
+* Scarce:: Coping with Scarce Resources
-@menu
-* Creating Example:: Creating Archives of Files
-* Subdirectory:: Creating an Archive of a Subdirectory
-@end menu
+Options to Help Read Archives
-@node Creating Example, Subdirectory, Creating Archives, Creating Archives
-@subsection Creating Archives of Files
+* read full records::
+* Ignore Zeros::
+* Ignore Failed Read::
-This example shows you how to create an archive file in the working
-directory containing other files in the working directory. The three
-files you archive in this example are called @file{blues},
-@file{folk}, and @file{jazz}. The archive file is called
-@file{records}. While the archive in this example is written to the
-file system, it could also be written to any other device.
+Changing How @code{tar} Writes Files
-(If you want to follow along with this and future examples, create a
-directory called @file{practice} containing files called @file{blues},
-@file{folk} and @file{jazz}. To create the directory, type
-@samp{mkdir practice} at the system prompt. It will probably be
-easiest to create the files using a text editor, such as Emacs.)
+* Prevention Overwriting::
+* Keep Old Files::
+* Unlink First::
+* Recursive Unlink::
+* Modification Times::
+* Setting Access Permissions::
+* Writing to Standard Output::
+* remove files::
-First, change into the directory containing the files you want to
-archive:
+Options to Prevent Overwriting Files
-@example
-% cd practice
-@end example
+* Keep Old Files::
+* Unlink First::
+* Recursive Unlink::
-@noindent
-@file{~/practice} is now your working directory.
+Coping with Scarce Resources
-Then, check that the files to be archived do in fact exist in the
-working directory, and make sure there isn't already a file in the
-working directory with the archive name you intend to use. If you
-specify an archive file name that is already in use, @code{tar} will
-overwrite the old file and its contents will be lost.
+* Starting File::
+* Same Order::
-To list the names of files in the working directory, type:
+Performing Backups and Restoring Files
-@example
-% ls
-@end example
+* Full Dumps:: Using @code{tar} to Perform Full Dumps
+* Inc Dumps:: Using @code{tar} to Perform Incremental Dumps
+* incremental and listed-incremental:: The Incremental Options
+* Backup Levels:: Levels of Backups
+* Backup Parameters:: Setting Parameters for Backups and Restoration
+* Scripted Backups:: Using the Backup Scripts
+* Scripted Restoration:: Using the Restore Script
-The system responds:
+Setting Parameters for Backups and Restoration
-@example
-blues folk jazz
-%
-@end example
+* backup-specs example:: An Example Text of @file{Backup-specs}
+* Script Syntax:: Syntax for @file{Backup-specs}
-@noindent
-Then,
-@itemize @bullet
-@item
-Create a new archive (@samp{tar -c} or @samp{tar +create})
+Choosing Files and Names for @code{tar}
-@item
-Explicitly name the archive file being created (@samp{-f
-@var{archive-name}} or @samp{+file=@var{archive-name}}). If you don't
-use this option @code{tar} will write the archive to the default
-storage device, which varies from system to system.
-@c <<< this syntax may change. OK now---check before printing -ringo
+* file:: Choosing the Archive's Name
+* Selecting Archive Members::
+* files:: Reading Names from a File
+* exclude:: Excluding Some Files
+* Wildcards::
+* after:: Operating Only on New Files
+* recurse:: Descending into Directories
+* one:: Crossing Filesystem Boundaries
-@code{tar} interprets archive file names relative to the working
-directory. Make sure you have write access to the working directory
-before using @code{tar}.
+Reading Names from a File
-@item
-Specify which files to put into the archive (@code{tar} interprets
-file names relative to the working directory). If you don't use any
-@var{file-name} arguments, @code{tar} will archive everything in the
-working directory.
-@end itemize
+* nul::
-@noindent
-Type:
-@example
-% tar +create +file=records blues folk jazz
-@end example
+Excluding Some Files
-@noindent
-If you now list the contents of the working directory (@samp{ls}), you
-will find the archive file listed as well as the files you saw
-previously.
+* problems with exclude::
-@example
-% ls
-blues folk jazz records
-%
-@end example
+Crossing Filesystem Boundaries
-@menu
-* Listing Files:: Listing files in an archive
-* Verbose:: Using @code{tar} in Verbose Mode
-@end menu
+* directory:: Changing Directory
+* absolute:: Absolute File Names
-@node Listing Files, Verbose, Creating Example, Creating Example
-@subsubsection Listing files in an archive
+Date input formats
-You can list the contents of an archive with another operation of
-@code{tar}---@samp{+list} or @samp{-l}. To list the contents of the
-archive you just created, type:
+* General date syntax:: Common rules.
+* Calendar date item:: 19 Dec 1994.
+* Time of day item:: 9:20pm.
+* Timezone item:: EST, DST, BST, UCT, AHST, ...
+* Day of week item:: Monday and others.
+* Relative item in date strings:: next tuesday, 2 years ago.
+* Pure numbers in date strings:: 19931219, 1440.
+* Authors of getdate:: Bellovin, Salz, Berets, et al.
-@example
-% tar +list +file=records
-@end example
+Controlling the Archive Format
-@noindent
-@code{tar} will respond:
+* Portability:: Making @code{tar} Archives More Portable
+* Compression:: Using Less Space through Compression
+* Attributes:: Handling File Attributes
+* Standard:: The Standard Format
+* Extensions:: GNU Extensions to the Archive Format
+* cpio:: Comparison of @code{tar} and @code{cpio}
-@example
-blues folk jazz
-@end example
+Making @code{tar} Archives More Portable
-@xref{Listing Archive Contents}, for a more detailed tutorial of the
-@samp{+list} operation. @xref{Listing Contents}, for more information
-about the @samp{+list} operation.
+* Portable Names:: Portable Names
+* dereference:: Symbolic Links
+* old:: Old V7 Archives
+* posix:: POSIX archives
+* Checksumming:: Checksumming Problems
-@node Verbose, , Listing Files, Creating Example
-@subsubsection Using @code{tar} in Verbose Mode
+Using Less Space through Compression
-If you include the @samp{+verbose} or @samp{-v} option on the command
-line, @code{tar} will list the files it is acting on as it is working.
-In verbose mode, the creation example above would appear as:
-@cindex Verbose mode example
-@findex -v (verbose mode example)
+* gzip:: Creating and Reading Compressed Archives
+* sparse:: Archiving Sparse Files
-@example
-% tar +create +file=records +verbose blues folk jazz
-blues
-folk
-jazz
-@end example
+Tapes and Other Archive Media
-@noindent
-The first line is the command typed in by the user. The remaining
-lines are generated by @code{tar}. In the following examples we
-usually use verbose mode, though it is almost never required.
-
-@node Subdirectory, Changing, Creating Example, Creating Archives
-@subsection Creating an Archive of a Subdirectory
-
-You can store a directory in an archive by using the directory name as
-a file-name argument to @code{tar}. When you specify a directory
-file, @code{tar} archives the directory file and all the files it
-contains. The names of the directory and the files it contains are
-stored in the archive relative to the current working directory---when
-the directory is extracted they will be written into the file system
-relative to the working directory at that time.
-@c <<< add an xref to +absolute-paths -ringo
+* Device:: Device selection and switching
+* Remote Tape Server::
+* Common Problems and Solutions::
+* Blocking:: Blocking
+* Many:: Many archives on one tape
+* Using Multiple Tapes:: Using Multiple Tapes
+* label:: Including a Label in the Archive
+* verify::
+* Write Protection::
-To archive a directory, first move to its superior directory. If you
-have been following the tutorial, you should type:
+Blocking
-@example
-% cd ..
-%
-@end example
+* Format Variations:: Format Variations
+* Blocking Factor:: The Blocking Factor of an Archive
-Once in the superior directory, specify the subdirectory using a
-file-name argument. To store the directory file @file{~/practice} in
-the archive file @file{music}, type:
+Many Archives on One Tape
-@example
-% tar +create +verbose +file=music practice
-@end example
+* Tape Positioning:: Tape Positions and Tape Marks
+* mt:: The @code{mt} Utility
-@noindent
-@code{tar} should respond:
+Using Multiple Tapes
-@example
-practice/
-practice/blues
-practice/folk
-practice/jazz
-practice/records
-@end example
+* Multi-Volume Archives:: Archives Longer than One Tape or Disk
+* Tape Files:: Tape Files
+@end menu
+
+@node Introduction, Tutorial, Top, Top
+@chapter Introduction
+
+Welcome to the GNU @code{tar} manual. GNU @code{tar} is used to create
+and manipulate files (@dfn{archives}) which are actually collections of
+many other files; the program provides users with an organized and
+systematic method for controlling a large amount of data.
+
+@menu
+* Book Contents:: What this Book Contains
+* Definitions:: Some Definitions
+* What tar Does:: What @code{tar} Does
+* Naming tar Archives:: How @code{tar} Archives are Named
+* posix compliance::
+* Authors:: GNU @code{tar} Authors
+* Reports:: Reporting bugs or suggestions
+@end menu
-Note that @file{~/practice/records}, another archive file, has
-itself been archived. @code{tar} will accept any file as a file to be
-archived, even an archive file.
+@node Book Contents, Definitions, Introduction, Introduction
+@ifinfo
+@heading What this Book Contains
+@end ifinfo
+
+The first part of this chapter introduces you to various terms that will
+recur throughout the book. It also tells you who has worked on GNU
+@code{tar} and its documentation, and where you should send bug reports
+or comments.
+
+The second chapter is a tutorial (@pxref{Tutorial}) which provides a
+gentle introduction for people who are new to using @code{tar}. It is
+meant to be self contained, not requiring any reading from subsequent
+chapters to make sense. It moves from topic to topic in a logical,
+progressive order, building on information already explained.
+
+Although the tutorial is paced and structured to allow beginners to
+learn how to use @code{tar}, it is not intended solely for beginners.
+The tutorial explains how to use the three most frequently used
+operations (@samp{create}, @samp{list}, and @samp{extract}) as well as
+two frequently used options (@samp{file} and @samp{verbose}). The other
+chapters do not refer to the tutorial frequently; however, if a section
+discusses something which is a complex variant of a basic concept, there
+may be a cross reference to that basic concept. (The entire book,
+including the tutorial, assumes that the reader understands some basic
+concepts of using a Unix-type operating system; @pxref{Tutorial}.)
+
+The third chapter presents the remaining five operations, and
+information about using @code{tar} options and option syntax.
+
+@FIXME{this sounds more like a GNU Project Manuals Concept [tm] more
+than the reality. should think about whether this makes sense to say
+here, or not.} The other chapters are meant to be used as a
+reference. Each chapter presents everything that needs to be said
+about a specific topic.
+
+One of the chapters (@pxref{Date input formats}) exists in its entirety
+in other GNU manuals, and is mostly self-contained. In addition, one
+section of this manual (@pxref{Standard}) contains a big quote which is
+taken directly from @code{tar} sources.
+
+In general, we give both the long and short (abbreviated) option names
+at least once in each section where the relevant option is covered, so
+that novice readers will become familiar with both styles. (A few
+options have no short versions, and the relevant sections will
+indicate this.)
+
+@node Definitions, What tar Does, Book Contents, Introduction
+@section Some Definitions
+
+@cindex archive
+@cindex tar archive
+The @code{tar} program is used to create and manipulate @code{tar}
+archives. An @dfn{archive} is a single file which contains the contents
+of many files, while still identifying the names of the files, their
+owner(s), and so forth. (In addition, archives record access
+permissions, user and group, size in bytes, and last modification time.
+Some archives also record the file names in each archived directory, as
+well as other file and directory information.) You can use @code{tar}
+to @dfn{create} a new archive in a specified directory.
+
+@cindex member
+@cindex archive member
+@cindex file name
+@cindex member name
+The files inside an archive are called @dfn{members}. Within this
+manual, we use the term @dfn{file} to refer only to files accessible in
+the normal ways (by @code{ls}, @code{cat}, and so forth), and the term
+@dfn{member} to refer only to the members of an archive. Similarly, a
+@dfn{file name} is the name of a file, as it resides in the filesystem,
+and a @dfn{member name} is the name of an archive member within the
+archive.
-@c >>> symbolic links and changing directories are now in main body, not in
-@c >>> tutorial. -ringo
+@cindex extraction
+@cindex unpacking
+The term @dfn{extraction} refers to the process of copying an archive
+member (or multiple members) into a file in the filesystem. Extracting
+all the members of an archive is often called @dfn{extracting the
+archive}. The term @dfn{unpack} can also be used to refer to the
+extraction of many or all the members of an archive. Extracting an
+archive does not destroy the archive's structure, just as creating an
+archive does not destroy the copies of the files that exist outside of
+the archive. You may also @dfn{list} the members in a given archive
+(this is often thought of as ``printing'' them to the standard output,
+or the command line), or @dfn{append} members to a pre-existing archive.
+All of these operations can be peformed using @code{tar}.
+
+@node What tar Does, Naming tar Archives, Definitions, Introduction
+@section What @code{tar} Does
+
+@cindex tar
+The @code{tar} program provides the ability to create @code{tar}
+archives, as well as various other kinds of manipulation. For example,
+you can use @code{tar} on previously created archives to extract files,
+to store additional files, or to update or list files which were already
+stored.
+
+Initially, @code{tar} archives were used to store files conveniently on
+magnetic tape. The name @samp{tar} comes from this use; it stands for
+@code{t}ape @code{ar}chiver. Despite the utility's name, @code{tar} can
+direct its output to available devices, files, or other programs (using
+pipes). @code{tar} may even access remote devices or files (as archives).
+
+@FIXME{the following table entries need a bit of work..}
+
+You can use @code{tar} archives in many ways. We want to stress a few
+of them: storage, backup, and transportation.
+
+@table @asis
+@item Storage
+Often, @code{tar} archives are used to store related files for
+convenient file transfer over a network. For example, the GNU Project
+distributes its software bundled into @code{tar} archives, so that
+all the files relating to a particular program (or set of related
+programs) can be transferred as a single unit.
+
+A magnetic tape can store several files in sequence. However, the tape
+has no names for these files; it only knows their relative position on
+the tape. One way to store several files on one tape and retain their
+names is by creating a @code{tar} archive. Even when the basic transfer
+mechanism can keep track of names, as FTP can, the nuisance of handling
+multiple files, directories, and multiple links makes @code{tar}
+archives useful.
+
+Archive files are also used for long-term storage. You can think of
+this as transportation from the present into the future. (It is a
+science-fiction idiom that you can move through time as well as in
+space; the idea here is that @code{tar} can be used to move archives in
+all dimensions, even time!)
+
+@item Backup
+Because the archive created by @code{tar} is capable of preserving file
+information and directory structure, @code{tar} is commonly used for
+performing full and incremental backups of disks. A backup puts a
+collection of files (possibly pertaining to many users and
+projects) together on a disk or a tape. This guards against accidental
+destruction of the information in those files. GNU @code{tar} has
+special features that allow it to be used to make incremental and full
+dumps of all the files in a filesystem.
+
+@item Transportation
+You can create an archive on one system, transfer it to another system,
+and extract the contents there. This allows you to transport a group of
+files from one system to another.
+@end table
-@node Extracting Files
-@section Extracting Files from an Archive
+@node Naming tar Archives, posix compliance, What tar Does, Introduction
+@section How @code{tar} Archives are Named
-Creating an archive is only half the job---there would be no point in
-storing files in an archive if you couldn't retrieve them. To extract
-files from an archive, use the @samp{+extract} or @samp{-x} operation.
+Conventionally, @code{tar} archives are given names ending with
+@samp{.tar}. This is not necessary for @code{tar} to operate properly,
+but this manual follows that convention in order to accustom readers to
+it and to make examples more clear.
-To extract specific files, use their names as file-name arguments. If
-you use a directory name as a file-name argument, @code{tar} extracts
-all the files (including subdirectories) in that directory. If you
-don't use any file-name arguments, @code{tar} extracts all the files
-in the archive.
+@cindex tar file
+@cindex entry
+@cindex tar entry
+Often, people refer to @code{tar} archives as ``@code{tar} files,'' and
+archive members as ``files'' or ``entries''. For people familiar with
+the operation of @code{tar}, this causes no difficulty. However, in
+this manual, we consistently refer to ``archives'' and ``archive
+members'' to make learning to use @code{tar} easier for novice users.
-Note: @code{tar} will extract an archive member into the file system
-without checking to see if there is already a file with the archive
-member's file name. If there is a file with that name, @code{tar}
-will @strong{overwrite} that file and its contents will be lost.
-@c <<<xref keep-old -ringo
+@node posix compliance, Authors, Naming tar Archives, Introduction
+@section POSIX Compliance
-@node Extracting Specific Files, , ,
-@subsection Extracting Specific Files
+@noindent
+@FIXME{must ask franc,ois about this. dan hagerty thinks this might
+be an issue, but we're not really sure at this time. dan just tried a
+test case of mixing up options' orders while the variable was set, and
+there was no problem...}
+
+We make some of our recommendations throughout this book for one
+reason in addition to what we think of as ``good sense''. The main
+additional reason for a recommendation is to be compliant with the
+POSIX standards. If you set the shell environment variable
+@code{POSIXLY_CORRECT}, GNU @code{tar} will force you to adhere to
+these standards. Therefore, if this variable is set and you violate
+one of the POSIX standards in the way you phrase a command, for
+example, GNU @code{tar} will not allow the command and will signal an
+error message. You would then have to reorder the options or rephrase
+the command to comply with the POSIX standards.
+
+There is a chance in the future that, if you set this environment
+variable, your archives will be forced to comply with POSIX standards,
+also. No GNU @code{tar} extensions will be allowed.
+
+@node Authors, Reports, posix compliance, Introduction
+@section GNU @code{tar} Authors
+
+GNU @code{tar} was originally written by John Gilmore, and modified by
+many people. The GNU enhancements were written by Jay Fenlason, then
+Joy Kendall, and the whole package has been further maintained by
+Thomas Bushnell, n/BSG, and finally Fran@,{c}ois Pinard, with
+the help of numerous and kind users.
+
+We wish to stress that @code{tar} is a collective work, and owes much to
+all those people who reported problems, offered solutions and other
+insights, or shared their thoughts and suggestions. An impressive, yet
+partial list of those contributors can be found in the @file{THANKS}
+file from the GNU @code{tar} distribution.
+
+@FIXME{i want all of these names mentioned, Absolutely. BUT, i'm not
+sure i want to spell out the history in this detail, at least not for
+the printed book. i'm just not sure it needs to be said this way.
+i'll think about it.}
+
+@FIXME{History is more important, and surely more interesting, than
+actual names. Quoting names without history would be meaningless. FP}
+
+Jay Fenlason put together a draft of a GNU @code{tar} manual,
+borrowing notes from the original man page from John Gilmore. This
+draft has been distributed in @code{tar} versions 1.04 (or even
+before?) @FIXME{huh? IMO, either we know or we don't; the
+parenthetical is confusing.} through 1.10, then withdrawn in version
+1.11. Thomas Bushnell, n/BSG and Amy Gorin worked on a tutorial and
+manual for GNU @code{tar}. Fran@,{c}ois Pinard put version 1.11.8
+of the manual together by taking information from all these sources
+and merging them. Melissa Weisshaus finally edited and redesigned the
+book to create version 1.12. @FIXME{update version number as
+necessary; i'm being optimistic!} @FIXME{Someone [maybe karl berry?
+maybe bob chassell? maybe melissa? maybe julie sussman?] needs to
+properly index the thing.}
+
+For version 1.12, Daniel Hagerty contributed a great deal of technical
+consulting. In particular, he is the primary author of @ref{Backups}.
+
+@node Reports, , Authors, Introduction
+@section Reporting bugs or suggestions
+
+@cindex bug reports
+@cindex reporting bugs
+If you find problems or have suggestions about this program or manual,
+please report them to @file{bug-tar@@gnu.org}.
+
+@node Tutorial, tar invocation, Introduction, Top
+@chapter Tutorial Introduction to @code{tar}
+
+This chapter guides you through some basic examples of three @code{tar}
+operations: @samp{--create}, @samp{--list}, and @samp{--extract}. If
+you already know how to use some other version of @code{tar}, then you
+may not need to read this chapter. This chapter omits most complicated
+details about how @code{tar} works.
-To extract specific files, specify them using file-name arguments.
+@menu
+* assumptions::
+* stylistic conventions::
+* basic tar options:: Basic @code{tar} Operations and Options
+* frequent operations::
+* Two Frequent Options::
+* create:: How to Create Archives
+* list:: How to List Archives
+* extract:: How to Extract Members from an Archive
+* going further::
+@end menu
-In an example above, you created the archive file
-@file{~/practice/records}, which contained the files @file{blues},
-@file{folk} and @file{jazz} in the @file{practice} directory. If, for
-some reason, you were to lose one of those text files (@samp{rm
-~/practice/blues}), you could extract it from the archive file.
+@node assumptions, stylistic conventions, Tutorial, Tutorial
+@ifinfo
+@heading Assumptions this Tutorial Makes
+@end ifinfo
-First, change into the @file{practice} directory. Then,
+This chapter is paced to allow beginners to learn about @code{tar}
+slowly. At the same time, we will try to cover all the basic aspects of
+these three operations. In order to accomplish both of these tasks, we
+have made certain assumptions about your knowledge before reading this
+manual, and the hardware you will be using:
@itemize @bullet
@item
-Invoke @code{tar} and specify the @samp{+extract} operation
-(@samp{+extract}, @samp{+get} or @samp{-x})
+Before you start to work through this tutorial, you should understand
+what the terms ``archive'' and ``archive member'' mean
+(@pxref{Definitions}). In addition, you should understand something
+about how Unix-type operating systems work, and you should know how to
+use some basic utilities. For example, you should know how to create,
+list, copy, rename, edit, and delete files and directories; how to
+change between directories; and how to figure out where you are in the
+filesystem. You should have some basic understanding of directory
+structure and how files are named according to which directory they are
+in. You should understand concepts such as standard output and standard
+input, what various definitions of the term ``argument'' mean, the
+differences between relative and absolute path names, and @FIXME{what
+else?}.
@item
-Specify the archive that the files will be extracted from
-(@samp{+file=@var{archive-name}} or @samp{-f @var{archive-name}})
+This manual assumes that you are working from your own home directory
+(unless we state otherwise). In this tutorial, you will create a
+directory to practice @code{tar} commands in. When we show path names,
+we will assume that those paths are relative to your home directory.
+For example, my home directory path is @file{/home/fsf/melissa}. All of
+my examples are in a subdirectory of the directory named by that path
+name; the subdirectory is called @file{practice}.
@item
-Specify the files to extract, using file-name arguments (if you don't
-specify any files, @code{tar} extracts all the archive members)
+In general, we show examples of archives which exist on (or can be
+written to, or worked with from) a directory on a hard disk. In most
+cases, you could write those archives to, or work with them on any other
+device, such as a tape drive. However, some of the later examples in
+the tutorial and next chapter will not work on tape drives.
+Additionally, working with tapes is much more complicated than working
+with hard disks. For these reasons, the tutorial does not cover working
+with tape drives. @xref{Media}, for complete information on using
+@code{tar} archives with tape drives.
+
+@FIXME{this is a cop out. need to add some simple tape drive info.}
@end itemize
+@node stylistic conventions, basic tar options, assumptions, Tutorial
+@ifinfo
+@heading Stylistic Conventions
+@end ifinfo
+
+In the examples, @samp{$} represents a typical shell prompt. It
+precedes lines you should type; to make this more clear, those lines are
+shown in @kbd{this font}, as opposed to lines which represent the
+computer's response; those lines are shown in @code{this font}, or
+sometimes @samp{like this}. When we have lines which are too long to be
+displayed in any other way, we will show them like this:
+
+@smallexample
+This is an example of a line which would otherwise not fit in this space.
+@end smallexample
+
+@FIXME{how often do we use smallexample?}
+
+@node basic tar options, frequent operations, stylistic conventions, Tutorial
+@section Basic @code{tar} Operations and Options
+
+@code{tar} can take a wide variety of arguments which specify and define
+the actions it will have on the particular set of files or the archive.
+The main types of arguments to @code{tar} fall into one of two classes:
+operations, and options.
+
+Some arguments fall into a class called @dfn{operations}; exactly one of
+these is both allowed and required for any instance of using @code{tar};
+you may @emph{not} specify more than one. People sometimes speak of
+@dfn{operating modes}. You are in a particular operating mode when you
+have specified the operation which specifies it; there are eight
+operations in total, and thus there are eight operating modes.
+
+The other arguments fall into the class known as @dfn{options}. You are
+not required to specify any options, and you are allowed to specify more
+than one at a time (depending on the way you are using @code{tar} at
+that time). Some options are used so frequently, and are so useful for
+helping you type commands more carefully that they are effectively
+``required''. We will discuss them in this chapter.
+
+You can write most of the @code{tar} operations and options in any of
+three forms: long (mnemonic) form, short form, and old style. Some of
+the operations and options have no short or ``old'' forms; however, the
+operations and options which we will cover in this tutorial have
+corresponding abbreviations. @FIXME{make sure this is still the case,
+at the end} We will indicate those abbreviations appropriately to get
+you used to seeing them. (Note that the ``old style'' option forms
+exist in GNU @code{tar} for compatibility with Unix @code{tar}. We
+present a full discussion of this way of writing options and operations
+appears in @ref{Old Options}, and we discuss the other two styles of
+writing options in @ref{Mnemonic Options} and @ref{Short Options}.)
+
+In the examples and in the text of this tutorial, we usually use the
+long forms of operations and options; but the ``short'' forms produce
+the same result and can make typing long @code{tar} commands easier.
+For example, instead of typing
+
@example
-% tar +extract +file=records blues
+@kbd{tar --create --verbose --file=afiles.tar apple angst aspic}
@end example
-If you list the contents of the directory, you will see that
-@file{blues} is back:
+@noindent
+you can type
+@example
+@kbd{tar -c -v -f afiles.tar apple angst aspic}
+@end example
+@noindent
+or even
@example
-% ls
-folk
-jazz
-records
-blues
+@kbd{tar -cvf afiles.tar apple angst aspic}
@end example
-@node Extracting Directories, , ,
-@subsection Extracting Directories
+@noindent
+For more information on option syntax, see @ref{Advanced tar}. In
+discussions in the text, when we name an option by its long form, we
+also give the corresponding short option in parentheses.
+
+The term, ``option'', can be confusing at times, since ``operations''
+are often lumped in with the actual, @emph{optional} ``options'' in certain
+general class statements. For example, we just talked about ``short and
+long forms of options and operations''. However, experienced @code{tar}
+users often refer to these by shorthand terms such as, ``short and long
+options''. This term assumes that the ``operations'' are included, also.
+Context will help you determine which definition of ``options'' to use.
+
+Similarly, the term ``command'' can be confusing, as it is often used in
+two different ways. People sometimes refer to @code{tar} ``commands''.
+A @code{tar} @dfn{command} is the entire command line of user input
+which tells @code{tar} what to do --- including the operation, options,
+and any arguments (file names, pipes, other commands, etc). However,
+you will also sometimes hear the term ``the @code{tar} command''. When
+the word ``command'' is used specifically like this, a person is usually
+referring to the @code{tar} @emph{operation}, not the whole line.
+Again, use context to figure out which of the meanings the speaker
+intends.
+
+@node frequent operations, Two Frequent Options, basic tar options, Tutorial
+@section The Three Most Frequently Used Operations
+
+Here are the three most frequently used operations (both short and long
+forms), as well as a brief description of their meanings. The rest of
+this chapter will cover how to use these operations in detail. We will
+present the rest of the operations in the next chapter.
+
+@table @kbd
+@item --create
+@itemx -c
+Create a new @code{tar} archive.
+@item --list
+@itemx -t
+List the contents of an archive.
+@item --extract
+@itemx -x
+Extract one or more members from an archive.
+@end table
+
+@node Two Frequent Options, create, frequent operations, Tutorial
+@section Two Frequently Used Options
+
+To understand how to run @code{tar} in the three operating modes listed
+previously, you also need to understand how to use two of the options to
+@code{tar}: @samp{--file} (which takes an archive file as an argument)
+and @samp{--verbose}. (You are usually not @emph{required} to specify
+either of these options when you run @code{tar}, but they can be very
+useful in making things more clear and helping you avoid errors.)
+
+@menu
+* file tutorial::
+* verbose tutorial::
+* help tutorial::
+@end menu
+
+@node file tutorial, verbose tutorial, Two Frequent Options, Two Frequent Options
+@unnumberedsubsec The @samp{--file} Option
-To extract a directory and all the files it contains, use the
-directory's name as a file-name argument in conjunction with @samp{tar
-+extract}. Remember---@code{tar} stores and extracts file names
-relative to the working directory.
+@table @kbd
+@item --file=@var{archive-name}
+@itemx -f @var{archive-name}
+Specify the name of an archive file.
+@end table
-In a previous example you stored the directory @file{~/practice} in
-the archive file @file{~/music}. If you delete the contents of
-@file{practice}, you can restore them using @code{tar}.
+You can specify an argument for the @value{op-file} option whenever you
+use @code{tar}; this option determines the name of the archive file
+that @code{tar} will work on.
-First, change into the @file{practice} subdirectory (@samp{cd
-~/practice}). Then, remove all the files in @samp{~/practice}
-(@samp{rm *}). If you list the contents of the directory, you should
-now see that it is empty:
+If you don't specify this argument, then @code{tar} will use a
+default, usually some physical tape drive attached to your machine.
+If there is no tape drive attached, or the default is not meaningful,
+then @code{tar} will print an error message. The error message might
+look roughly like one of the following:
@example
-%ls
-%
+tar: can't open /dev/rmt8 : No such device or address
+tar: can't open /dev/rsmt0 : I/O error
@end example
-@noindent Let's try to restore the contents of @file{practice} by extracting
-them from the archive file @file{~/music}:
+@noindent
+To avoid confusion, we recommend that you always specfiy an archive file
+name by using @value{op-file} when writing your @code{tar} commands.
+For more information on using the @value{op-file} option, see
+@ref{file}.
+
+@node verbose tutorial, help tutorial, file tutorial, Two Frequent Options
+@unnumberedsubsec The @samp{--verbose} Option
+
+@table @kbd
+@item --verbose
+@itemx -v
+Show the files being worked on as @code{tar} is running.
+@end table
+
+@value{op-verbose} shows details about the results of running
+@code{tar}. This can be especially useful when the results might not be
+obvious. For example, if you want to see the progress of @code{tar} as
+it writes files into the archive, you can use the @samp{--verbose}
+option. In the beginning, you may find it useful to use
+@samp{--verbose} at all times; when you are more accustomed to
+@code{tar}, you will likely want to use it at certain times but not at
+others. We will use @samp{--verbose} at times to help make something
+clear, and we will give many examples both using and not using
+@samp{--verbose} to show the differences.
+
+Sometimes, a single instance of @samp{--verbose} on the command line
+will show a full, @samp{ls} style listing of an archive or files,
+giving sizes, owners, and similar information. Other times,
+@samp{--verbose} will only show files or members that the particular
+operation is operating on at the time. In the latter case, you can
+use @samp{--verbose} twice in a command to get a listing such as that
+in the former case. For example, instead of saying
@example
-tar +extract +file=~/music practice
+@kbd{tar -cvf afiles.tar apple angst aspic}
@end example
-@noindent Now, list the contents of @file{practice} again:
+@noindent
+above, you might say
@example
-%ls
-practice
+@kbd{tar -cvvf afiles.tar apple angst aspic}
@end example
-What happened to the files? When you created @file{~/music}, your
-working directory was your home directory. When you extracted
-@file{~/music}, your working directory was @file{~/practice}.
-@code{tar} stored the files in @file{practice} relative to your home
-directory, and then extracted them relative to @file{~/practice}. The
-files are now in a new subdirectory, called
-@file{~/practice/practice}.
-
-To restore your files to their old positions, delete the new directory
-and its contents, and then redo the example above with your home
-directory as the working directory:
+@noindent
+This works equally well using short or long forms of options. Using
+long forms, you would simply write out the mnemonic form of the option
+twice, like this:
@example
-% rm ~/practice/practice/*
-% rmdir practice
-% cd ..
-% tar +extract +file=music practice
+$ @kbd{tar --create --verbose --verbose @dots{}}
@end example
-@noindent (@code{tar} will report that it is unable to create the
-directory @file{~/practice} because it already exists. This will not
-effect the extraction of the other archive members.)
+@noindent
+Note that you must double the hyphens properly each time.
+
+Later in the tutorial, we will give examples using @w{@samp{--verbose
+--verbose}}.
+
+@node help tutorial, , verbose tutorial, Two Frequent Options
+@unnumberedsubsec Getting Help: Using the @code{--help} Option
-@node Listing Archive Contents, Adding to Archives, Creating Archives, Tutorial
-@section Listing the Contents of an Archive
+@table @kbd
+@item --help
-Use @samp{+list} or @samp{-t} to print the names of files stored in an
-archive. If you use file-name arguments with this operation,
-@code{tar} prints the names of the specified files if they are stored
-in the archive. If you use a directory name as a file-name argument,
-@code{tar} also prints the names of all underlying files, including
-sub-directories. If you use no file-name arguments, @code{tar} prints
-the names of all the archive members.
+The @samp{--help} option to @code{tar} prints out a very brief list of
+all operations and option available for the current version of
+@code{tar} available on your system.
+@end table
-You can use @samp{+list} with the @samp{+verbose} option to print
-archive members' attributes (owner, size, etc.).
+@node create, list, Two Frequent Options, Tutorial
+@section How to Create Archives
+@UNREVISED
+
+One of the basic operations of @code{tar} is @value{op-create}, which
+you use to create a @code{tar} archive. We will explain
+@samp{--create} first because, in order to learn about the other
+operations, you will find it useful to have an archive available to
+practice on.
+
+To make this easier, in this section you will first create a directory
+containing three files. Then, we will show you how to create an
+@emph{archive} (inside the new directory). Both the directory, and
+the archive are specifically for you to practice on. The rest of this
+chapter and the next chapter will show many examples using this
+directory and the files you will create: some of those files may be
+other directories and other archives.
+
+The three files you will archive in this example are called
+@file{blues}, @file{folk}, and @file{jazz}. The archive is called
+@file{collection.tar}.
+
+This section will proceed slowly, detailing how to use @samp{--create}
+in @code{verbose} mode, and showing examples using both short and long
+forms. In the rest of the tutorial, and in the examples in the next
+chapter, we will proceed at a slightly quicker pace. This section
+moves more slowly to allow beginning users to understand how
+@code{tar} works.
@menu
-* Listing names:: Listing the names of stored files
-* Additional File Info:: Getting Additional File Information
-* Specific File:: List A Specific File in an Archive
-* Listing Directories:: Listing the Contents of a Stored Directory
+* prepare for examples::
+* Creating the archive::
+* create verbose::
+* short create::
+* create dir::
@end menu
-@node Listing names, Additional File Info, Listing Archive Contents, Listing Archive Contents
-@subsection Listing the names of stored files
-
-To list the names of files stored in an archive, use the @samp{+list}
-operation of @code{tar}.
+@node prepare for examples, Creating the archive, create, create
+@subsection Preparing a Practice Directory for Examples
+
+To follow along with this and future examples, create a new directory
+called @file{practice} containing files called @file{blues}, @file{folk}
+and @file{jazz}. The files can contain any information you like:
+ideally, they should contain information which relates to their names,
+and be of different lengths. Our examples assume that @file{practice}
+is a subdirectory of your home directory.
+
+Now @code{cd} to the directory named @file{practice}; @file{practice}
+is now your @dfn{working directory}. (@emph{Please note}: Although
+the full path name of this directory is
+@file{/@var{homedir}/practice}, in our examples we will refer to
+this directory as @file{practice}; the @var{homedir} is presumed.
+
+In general, you should check that the files to be archived exist where
+you think they do (in the working directory) by running @code{ls}.
+Because you just created the directory and the files and have changed to
+that directory, you probably don't need to do that this time.
+
+It is very important to make sure there isn't already a file in the
+working directory with the archive name you intend to use (in this case,
+@samp{collection.tar}), or that you don't care about its contents.
+Whenever you use @samp{create}, @code{tar} will erase the current
+contents of the file named by @value{op-file} if it exists. @code{tar}
+will not tell you if you are about to overwrite a file unless you
+specify an option which does this @FIXME{xref to the node for
+--backup!}. To add files to an existing archive, you need to use a
+different option, such as @value{op-append}; see @ref{append} for
+information on how to do this.
+
+@node Creating the archive, create verbose, prepare for examples, create
+@subsection Creating the Archive
+
+To place the files @file{blues}, @file{folk}, and @file{jazz} into an
+archive named @file{collection.tar}, use the following command:
-In a previous example, you created the archive @file{~/music}. To
-list the contents of @file{music}, while in your home directory:
+@example
+$ @kbd{tar --create --file=collection.tar blues folk jazz}
+@end example
-@itemize @bullet
-@item
-List the contents of an archive (@samp{tar -t} or @samp{tar +list})
+The order of the arguments is not very important, @emph{when using long
+option forms}. You could also say:
-@item
-Specify the archive to be listed (@samp{-f @var{archive-name}} or
-@samp{+file=@var{archive-name}}) @refill
-@end itemize
+@example
+$ @kbd{tar blues --create folk --file=collection.tar jazz}
+@end example
-Thus:
+@noindent
+However, you can see that this order is harder to understand; this is
+why we will list the arguments in the order that makes the commands
+easiest to understand (and we encourage you to do the same when you use
+@code{tar}, to avoid errors).
+
+Note that the part of the command which says,
+@w{@kbd{--file=collection.tar}} is considered to be @emph{one} argument.
+If you substituted any other string of characters for
+@kbd{`collection.tar'}, then that string would become the name of the
+archive file you create.
+
+The order of the options becomes more important when you begin to use
+short forms. With short forms, if you type commands in the wrong order
+(even if you type them correctly in all other ways), you may end up with
+results you don't expect. For this reason, it is a good idea to get
+into the habit of typing options in the order that makes inherent sense.
+@xref{short create}, for more information on this.
+
+In this example, you type the command as shown above: @samp{--create}
+is the operation which creates the new archive
+(@file{collection.tar}), and @samp{--file} is the option which lets
+you give it the name you chose. The files, @file{blues}, @file{folk},
+and @file{jazz}, are now members of the archive, @file{collection.tar}
+(they are @dfn{file name arguments} to the @samp{--create} operation)
+@FIXME{xref here to the discussion of file name args?}. Now that they
+are are in the archive, they are called @emph{archive members}, not
+files @FIXME{xref to definitions?}.
+
+When you create an archive, you @emph{must} specify which files you want
+placed in the archive. If you do not specify any archive members, GNU
+@code{tar} will complain.
+
+If you now list the contents of the working directory (@kbd{ls}), you will
+find the archive file listed as well as the files you saw previously:
@example
-% tar +list +file=music
-practice/
-practice/blues
-practice/folk
-practice/jazz
-practice/records
+blues folk jazz collection.tar
@end example
-@node Additional File Info, Specific File, Listing names, Listing Archive Contents
-@subsection Listing Additional File Information
-
-To get more information when you list the names of files stored in an
-archive, specify the @samp{+verbose} option in conjunction with
-@samp{tar +list}. @code{tar} will print archive member's file
-protection, owner and group ID, size, and date and time of creation.
+@noindent
+Creating the archive @samp{collection.tar} did not destroy the copies of
+the files in the directory.
-For example:
+Keep in mind that if you don't indicate an operation, @code{tar} will not
+run and will prompt you for one. If you don't name any files, @code{tar}
+will complain. You must have write access to the working directory,
+or else you will not be able to create an archive in that directory.
-@example
-% tar +list +verbose +file=music
-drwxrwxrwx myself/user 0 May 31 21:49 1990 practice/
--rw-rw-rw- myself/user 42 May 21 13:29 1990 practice/blues
--rw-rw-rw- myself/user 62 May 23 10:55 1990 practice/folk
--rw-rw-rw- myself/user 40 May 21 13:30 1990 practice/jazz
--rw-rw-rw- myself/user 10240 May 31 21:49 1990 practice/records
-%
-@end example
+@emph{Caution}: Do not attempt to use @value{op-create} to add files to
+an existing archive; it will delete the archive and write a new one.
+Use @value{op-append} instead. @xref{append}.
-Note that when you use @samp{+verbose} with @samp{+list}, @code{tar}
-doesn't print the names of files as they are being acted on, though
-the @samp{+verbose} option will have this effect when used with all
-other operations.
+@node create verbose, short create, Creating the archive, create
+@subsection Running @samp{--create} with @samp{--verbose}
-@node Specific File, Comparing Files, Additional File Info, Listing Archive Contents
-@subsection List A Specific File in an Archive
+If you include the @value{op-verbose} option on the command line,
+@code{tar} will list the files it is acting on as it is working. In
+verbose mode, the @code{create} example above would appear as:
-To to see if a particular file is in an archive, use the name of the
-file in question as a file-name argument while specifying the
-@samp{+list} operation. For example, to see whether the file
-@file{folk} is in the archive file @file{music}, do the following:
+@example
+$ @kbd{tar --create --verbose --file=collection.tar blues folk jazz}
+blues
+folk
+jazz
+@end example
-@itemize @bullet
-@item
-Invoke @code{tar}, and specify the @samp{+list} operation
-(@samp{+list} or @samp{-t}).
+This example is just like the example we showed which did not use
+@samp{--verbose}, except that @code{tar} generated the remaining lines
+@iftex
+(note the different font styles).
+@end iftex
+@ifinfo
+.
+@end ifinfo
-@item
-Specify the archive file to be acted on (@samp{+file
-@var{archive-name}} or @samp{-f @var{archive-name}}).
+In the rest of the examples in this chapter, we will frequently use
+@code{verbose} mode so we can show actions or @code{tar} responses that
+you would otherwise not see, and which are important for you to
+understand.
-@item
-Specify the files to look for, by typing their names as file-name
-arguments. You have to type the file name as it appears in the
-archive (normally, as it is relative to the relative to the directory
-from which the archive was created). <<< xref absolute-paths -ringo
-@end itemize
+@node short create, create dir, create verbose, create
+@subsection Short Forms with @samp{create}
-Type:
+As we said before, the @value{op-create} operation is one of the most
+basic uses of @code{tar}, and you will use it countless times.
+Eventually, you will probably want to use abbreviated (or ``short'')
+forms of options. A full discussion of the three different forms that
+options can take appears in @ref{Styles}; for now, here is what the
+previous example (including the @value{op-verbose} option) looks like
+using short option forms:
@example
-% tar +list +file=music practice/folk
+$ @kbd{tar -cvf collection.tar blues folk jazz}
+blues
+folk
+jazz
@end example
-@noindent
-@code{tar} responds:
+@noindent
+As you can see, the system responds the same no matter whether you use
+long or short option forms.
+
+@FIXME{i don't like how this is worded:} One difference between using
+short and long option forms is that, although the exact placement of
+arguments following options is no more specific when using short forms,
+it is easier to become confused and make a mistake when using short
+forms. For example, suppose you attempted the above example in the
+following way:
@example
-practice/folk
+$ @kbd{tar -cfv collection.tar blues folk jazz}
@end example
@noindent
-If the file were not stored in the archive (for example, the file
-@file{practice/rock}), the example above would look like:
+In this case, @code{tar} will make an archive file called @file{v},
+containing the files @file{blues}, @file{folk}, and @file{jazz}, because
+the @samp{v} is the closest ``file name'' to the @samp{-f} option, and
+is thus taken to be the chosen archive file name. @code{tar} will try
+to add a file called @file{collection.tar} to the @file{v} archive file;
+if the file @file{collection.tar} did not already exist, @code{tar} will
+report an error indicating that this file does not exist. If the file
+@file{collection.tar} does already exist (e.g., from a previous command
+you may have run), then @code{tar} will add this file to the archive.
+Because the @samp{-v} option did not get registered, @code{tar} will not
+run under @samp{verbose} mode, and will not report its progress.
+
+The end result is that you may be quite confused about what happened,
+and possibly overwrite a file. To illustrate this further, we will show
+you how an example we showed previously would look using short forms.
+
+This example,
@example
-% tar +list +file=music practice/rock
-tar: practice/rock not found in archive
+$ @kbd{tar blues --create folk --file=collection.tar jazz}
@end example
@noindent
-If you had used @samp{+verbose} mode, the example above would look
-like:
+is confusing as it is. When shown using short forms, however, it
+becomes much more so:
@example
-% tar +list +file=music practice/folk
--rw-rw-rw- myself/user 62 May 23 10:55 1990 practice/folk
+$ @kbd{tar blues -c folk -f collection.tar jazz}
@end example
-@node Listing Directories, , ,
-@subsection Listing the Contents of a Stored Directory
-
-To get information about the contents of an archived directory, use
-the directory name as a file-name argument in conjunction with
-@samp{+list}. To find out file attributes, include the
-@samp{+verbose} option.
+@noindent
+It would be very easy to put the wrong string of characters
+immediately following the @samp{-f}, but doing that could sacrifice
+valuable data.
+
+For this reason, we recommend that you pay very careful attention to
+the order of options and placement of file and archive names,
+especially when using short option forms. Not having the option name
+written out mnemonically can affect how well you remember which option
+does what, and therefore where different names have to be placed.
+(Placing options in an unusual order can also cause @code{tar} to
+report an error if you have set the shell environment variable,
+@code{POSIXLY_CORRECT}; @pxref{posix compliance} for more information
+on this.)
+
+@node create dir, , short create, create
+@subsection Archiving Directories
+
+@cindex Archiving Directories
+@cindex Directories, Archiving
+You can archive a directory by specifying its directory name as a
+file name argument to @code{tar}. The files in the directory will be
+archived relative to the working directory, and the directory will be
+re-created along with its contents when the archive is extracted.
-For example, to find out about files in the directory @file{practice},
-in the archive file @file{music}, type:
+To archive a directory, first move to its superior directory. If you
+have followed the previous instructions in this tutorial, you should
+type:
@example
-% tar +list +file=music practice
+$ @kbd{cd ..}
+$
@end example
-@noindent @code{tar} responds:
+@noindent
+This will put you into the directory which contains @file{practice},
+i.e. your home directory. Once in the superior directory, you can
+specify the subdirectory, @file{practice}, as a file name argument. To
+store @file{practice} in the new archive file @file{music.tar}, type:
@example
-drwxrwxrwx myself/user 0 May 31 21:49 1990 practice/
--rw-rw-rw- myself/user 42 May 21 13:29 1990 practice/blues
--rw-rw-rw- myself/user 62 May 23 10:55 1990 practice/folk
--rw-rw-rw- myself/user 40 May 21 13:30 1990 practice/jazz
--rw-rw-rw- myself/user 10240 May 31 21:49 1990 practice/records
+$ @kbd{tar --create --verbose --file=music.tar practice}
@end example
-When you use a directory name as a file-name argument, @code{tar} acts
-on all the files (including sub-directories) in that directory.
-
-@node Comparing Files, , ,
-@section Comparing Files in an Archive with Files in the File System
-
-To compare the attributes of archive members with the attributes of
-their counterparts in the file system, use the @samp{+compare},
-@samp{+diff}, or @samp{-d}) operation. While you could use
-@samp{+list +verbose} to manually compare some file attributes, it is
-simpler to have @code{tar} itself compare file attributes and report
-back on file differences.
-@c <<<"manually"? suggestions? -ringo
-
-The @samp{+compare} operation, as its name implies, compares archive
-members with files of the same name in the file system, and reports
-back differences in file size, mode, owner and modification date.
-@samp{tar +compare} acts only on archive members---it ignores files in
-the file system that are not stored in the archive. If you give
-@samp{tar +compare} a file-name argument that does not correspond to
-the name of an archive member, @code{tar} responds with an error
-message.
-
-To compare archive members in the archive file @file{records} with
-files in the @file{~/practice} directory, first change into the
-@file{practice} directory. Then:
-
-@itemize @bullet
-@item
-Invoke @code{tar} and specify the @samp{+compare} operation.
-(@samp{+compare}, @samp{+diff}, or @samp{-d}).
+@noindent
+@code{tar} should output:
-@item
-Specify the archive where the files to be compared are stored
-(@samp{+file=@var{archive-name}} or @samp{-f @var{archive-name}})
+@example
+practice/
+practice/blues
+practice/folk
+practice/jazz
+practice/collection.tar
+@end example
-@item
-Specify the archive members to be compared. (In this example you are
-comparing all the archive members in the archive. Since this is the
-default, you don't need to use any file-name arguments).
-@end itemize
+Note that the archive thus created is not in the subdirectory
+@file{practice}, but rather in the current working directory---the
+directory from which @code{tar} was invoked. Before trying to archive a
+directory from its superior directory, you should make sure you have
+write access to the superior directory itself, not only the directory
+you are trying archive with @code{tar}. For example, you will probably
+not be able to store your home directory in an archive by invoking
+@code{tar} from the root directory; @value{xref-absolute-names}. (Note
+also that @file{collection.tar}, the original archive file, has itself
+been archived. @code{tar} will accept any file as a file to be
+archived, regardless of its content. When @file{music.tar} is
+extracted, the archive file @file{collection.tar} will be re-written
+into the file system).
+
+If you give @code{tar} a command such as
@example
-% tar +compare +file=records
-%
+$ @kbd{tar --create --file=foo.tar .}
@end example
@noindent
-While it looks like nothing has happened, @code{tar} has, in fact,
-done the comparison---and found nothing to report.
-
-Use the @samp{+verbose} option to list the names of archive members as
-they are being compared with their counterparts of the same name in
-the file system:
+@code{tar} will report @samp{tar: foo.tar is the archive; not dumped}.
+This happens because @code{tar} creates the archive @file{foo.tar} in
+the current directory before putting any files into it. Then, when
+@code{tar} attempts to add all the files in the directory @file{.} to
+the archive, it notices that the file @file{foo.tar} is the same as the
+archive, and skips it. (It makes no sense to put an archive into
+itself.) GNU @code{tar} will continue in this case, and create the
+archive normally, except for the exclusion of that one file.
+(@emph{Please note:} Other versions of @code{tar} are not so clever;
+they will enter an infinite loop when this happens, so you should not
+depend on this behavior unless you are certain you are running GNU
+@code{tar}. @FIXME{bob doesn't like this sentence, since he does it
+all the time, and we've been doing it in the editing passes for this
+manual: In general, make sure that the archive is not inside a
+directory being dumped.})
+
+@node list, extract, create, Tutorial
+@section How to List Archives
+
+Frequently, you will find yourself wanting to determine exactly what a
+particular archive contains. You can use the @value{op-list} operation
+to get the member names as they currently appear in the archive, as well
+as various attributes of the files at the time they were archived. For
+example, you can examine the archive @file{collection.tar} that you
+created in the last section with the command,
@example
-% tar +compare +verbose +file=records
-blues
-folk
-jazz
-%
+$ @kbd{tar --list --file=collection.tar}
@end example
@noindent
-If @code{tar} had had anything to report, it would have done so as it
-was comparing each file.
-
-If you remove the file @file{jazz} from the file system (@samp{rm
-jazz}), and modify the file @file{blues} (for instance, by adding text
-to it with an editor such as Emacs), the above example would look
-like:
+The output of @code{tar} would then be:
@example
-% tar +compare +verbose +file=records
blues
-blues: mod time differs
-blues: size differs
folk
jazz
-jazz: does not exist
-%
@end example
-Note again that while @samp{tar +compare} reports the names of archive
-members that do not have counterparts in the file system, @samp{tar
-+compare} ignores files in the file system that do not have
-counterparts in the archive. To demonstrate this, create a file in
-the @file{practice} directory called @file{rock} (using any text
-editor). The new file appears when you list the directory's contents:
-
-@example
-% ls
-blues folk records rock
-@end example
+@FIXME{we hope this will change. if it doesn't, need to show the
+creation of bfiles somewhere above!!! : }
@noindent
-If you type the @samp{+compare} example again, @code{tar} prints the
-following:
+The archive @file{bfiles.tar} would list as follows:
@example
-% tar +compare +verbose +file=records
-blues
-blues: mod time differs
-blues: size differs
-folk
-jazz
-jazz: does not exist
-%
+./birds
+baboon
+./box
@end example
@noindent
-@code{tar} ignores the file @file{rock} because @code{tar} is
-comparing archive members to files in the file system, not vice versa.
+Be sure to use a @value{op-file} option just as with @value{op-create}
+to specify the name of the archive.
+
+If you use the @value{op-verbose} option with @samp{--list}, then
+@code{tar} will print out a listing reminiscent of @w{@samp{ls -l}},
+showing owner, file size, and so forth.
-If you specify @file{rock} explicitly (using a file-name argument),
-@code{tar} prints an error message:
+If you had used @value{op-verbose} mode, the example above would look
+like:
@example
-% tar +compare +verbose +file=records rock
-tar: rock not found in archive
-%
+$ @kbd{tar --list --verbose --file=collection.tar folk}
+-rw-rw-rw- myself user 62 1990-05-23 10:55 folk
@end example
+@cindex File name arguments, using @code{--list} with
+@cindex @code{--list} with file name arguments
+You can specify one or more individual member names as arguments when
+using @samp{list}. In this case, @code{tar} will only list the
+names of members you identify. For example, @w{@kbd{tar --list
+--file=afiles.tar apple}} would only print @file{apple}.
+
+@FIXME{we hope the relevant aspects of this will change:}Because
+@code{tar} preserves paths, file names must be specified as they appear
+in the archive (ie., relative to the directory from which the archive
+was created). Therefore, it is essential when specifying member names
+to @code{tar} that you give the exact member names. For example,
+@w{@kbd{tar --list --file=bfiles birds}} would produce an error message
+something like @samp{tar: birds: Not found in archive}, because there is
+no member named @file{birds}, only one named @file{./birds}. While the
+names @file{birds} and @file{./birds} name the same file, @emph{member}
+names are compared using a simplistic name comparison, in which an exact
+match is necessary. @xref{absolute}.
+
+However, @w{@kbd{tar --list --file=collection.tar folk}} would respond
+with @file{folk}, because @file{folk} is in the archive file
+@file{collection.tar}. If you are not sure of the exact file name, try
+listing all the files in the archive and searching for the one you
+expect to find; remember that if you use @samp{--list} with no file
+names as arguments, @code{tar} will print the names of all the members
+stored in the specified archive.
+
@menu
-* Comparing Directories:: Using Compare on Directories
+* list dir::
@end menu
-@node Comparing Directories, , ,
-@subsubsection Using Compare on Directories
+@node list dir, , list, list
+@unnumberedsubsec Listing the Contents of a Stored Directory
+@UNREVISED
-In addition to using @samp{+compare} to compare text files, you can
-use @samp{+compare} to compare directories. To illustrate this,
-re-create the examples above using your home directory as the working
-directory, and using the archive file @file{~/music} instead of the
-archive file @file{~/practice/records}.
+@FIXME{i changed the order of these nodes around and haven't had a
+chance to play around with this node's example, yet. i have to play
+with it and see what it actually does for my own satisfaction, even if
+what it says *is* correct..}
-First, change into your home directory (@samp{cd ~}). Then, try the
-above example using @file{music} as the specified archive file, and
-@file{practice} as a file-name argument.
+To get information about the contents of an archived directory,
+use the directory name as a file name argument in conjunction with
+@value{op-list}. To find out file attributes, include the
+@value{op-verbose} option.
+
+For example, to find out about files in the directory @file{practice}, in
+the archive file @file{music.tar}, type:
@example
-% tar +compare +verbose +file=music practice
+$ @kbd{tar --list --verbose --file=music.tar practice}
@end example
-@noindent
-If you have been following along with the tutorial, @code{tar} will
-respond:
+@code{tar} responds:
@example
-practice
-practice/blues
-practice/blues: mod time differs
-practice/blues: size differs
-practice/folk
-practice/jazz
-practice/jazz: does not exist
-practice/records
+drwxrwxrwx myself user 0 1990-05-31 21:49 practice/
+-rw-rw-rw- myself user 42 1990-05-21 13:29 practice/blues
+-rw-rw-rw- myself user 62 1990-05-23 10:55 practice/folk
+-rw-rw-rw- myself user 40 1990-05-21 13:30 practice/jazz
+-rw-rw-rw- myself user 10240 1990-05-31 21:49 practice/collection.tar
@end example
-@node Adding to Archives, Concatenate, Listing Archive Contents, Tutorial
-@section Adding Files to Existing Archives
+When you use a directory name as a file name argument, @code{tar} acts on
+all the files (including sub-directories) in that directory.
-@c >>> we want people to use the script for backups, so I an not going to
-@c >>> use backups as an explanation in the tutorial. (people can still
-@c >>> do it if they really want to) -ringo
+@node extract, going further, list, Tutorial
+@section How to Extract Members from an Archive
+@UNREVISED
+@cindex Extraction
+@cindex Retrieving files from an archive
+@cindex Resurrecting files from an archive
-While you can use @code{tar} to create a new archive every time you
-want to store a file, it is more sometimes efficient to add files to
-an existing archive.
+Creating an archive is only half the job---there is no point in storing
+files in an archive if you can't retrieve them. The act of retrieving
+members from an archive so they can be used and manipulated as
+unarchived files again is called @dfn{extraction}. To extract files
+from an archive, use the @value{op-extract} operation. As with
+@value{op-create}, specify the name of the archive with @value{op-file}.
+Extracting an archive does not modify the archive in any way; you can
+extract it multiple times if you want or need to.
-To add new files to an existing archive, use the @samp{+add-file},
-@samp{+append} or @samp{-r} operation. To add newer versions of
-archive members to an archive, use the @samp{+update} or @samp{-u}
-operation.
+Using @samp{--extract}, you can extract an entire archive, or specific
+files. The files can be directories containing other files, or not. As
+with @value{op-create} and @value{op-list}, you may use the short or the
+long form of the operation without affecting the performance.
@menu
-* Append:: Appending Files to an Archive
-* Update:: Updating Files in an Archive
+* extracting archives::
+* extracting files::
+* extract dir::
+* failing commands::
@end menu
-@node Append, Update, Adding to Archives, Adding to Archives
-@subsection Appending Files to an Archive
-
-The simplest method of adding a file to an existing archive is the
-@samp{+add-file}, @samp{-r} or @samp{+append} operation, which writes
-files into the archive without regard to whether or not they are
-already archive members. When you use @samp{+add-file} you must use
-file-name arguments; there is no default. If you specify a file that
-is already stored in the archive, @code{tar} adds another copy of the
-file to the archive.
-
-If you have been following the previous examples, you should have a
-text file called @file{~/practice/rock} which has not been stored in
-either the archive file @file{~/practice/records}, or the archive file
-@file{~/music}. To add @file{rock} to @file{records}, first make
-@file{practice} the working directory (@samp{cd practice}). Then:
-
-@itemize @bullet
-@item
-Invoke @code{tar} and specify the @samp{+add-file} operation
-(@samp{+add-file}, @samp{-r} or @samp{+append})
-
-@item
-Specify the archive to which the file will be added
-(@samp{+file=@var{archive-name}} or @samp{-f @var{archive-name}})
-
-@item
-Specify the files to be added to the archive, using file-name
-arguments
-@end itemize
+@node extracting archives, extracting files, extract, extract
+@subsection Extracting an Entire Archive
-@noindent
-For example:
+To extract an entire archive, specify the archive file name only, with
+no individual file names as arguments. For example,
@example
-% tar +add-file +file=records rock
+$ @kbd{tar -xvf collection.tar}
@end example
@noindent
-If you list the archive members in @file{records}, you will see that
-@file{rock} has been added to the archive:
+produces this:
@example
-% tar +list +file=records
-blues
-folk
-jazz
-rock
+-rw-rw-rw- me user 28 1996-10-18 16:31 jazz
+-rw-rw-rw- me user 21 1996-09-23 16:44 blues
+-rw-rw-rw- me user 20 1996-09-23 16:44 folk
@end example
-@c <<< this should be some kind of node.
+@node extracting files, extract dir, extracting archives, extract
+@subsection Extracting Specific Files
+
+To extract specific archive members, give their exact member names as
+arguments, as printed by @value{op-list}. If you had mistakenly deleted
+one of the files you had placed in the archive @file{collection.tar}
+earlier (say, @file{blues}), you can extract it from the archive without
+changing the archive's structure. It will be identical to the original
+file @file{blues} that you deleted. @FIXME{check this; will the times,
+permissions, owner, etc be the same, also?}
-You can use @samp{+add-file} to keep archive members current with
-active files. Because @samp{+add-file} stores a file whether or not
-there is already an archive member with the same file name, you can
-use @samp{+add-file} to add newer versions of archive members to an
-archive. When you extract the file, only the version stored last will
-wind up in the file system. Because @samp{tar +extract} extracts
-files from an archive in sequence, and overwrites files with the same
-name in the file system, if a file name appears more than once in an
-archive the last version of the file will overwrite the previous
-versions which have just been extracted.
+First, make sure you are in the @file{practice} directory, and list the
+files in the directory. Now, delete the file, @samp{blues}, and list
+the files in the directory again.
-If you recall from the examples using @samp{+compare} above,
-@file{blues} was changed after the archive @file{records} was created.
-It is simple, however, to use @samp{+add-file} to add the new version
-of @file{blues} to @file{records}:
+You can now extract the member @file{blues} from the archive file
+@file{collection.tar} like this:
@example
-% tar +add-file +verbose +file=records blues
-blues
+$ @kbd{tar --extract --file=collection.tar blues}
@end example
@noindent
-If you now list the contents of the archive, you will obtain the following:
+If you list the files in the directory again, you will see that the file
+@file{blues} has been restored, with its original permissions, creation
+times, and owner. @FIXME{This is only accidentally true, but not in
+general. In most cases, one has to be root for restoring the owner, and
+use a special option for restoring permissions. Here, it just happens
+that the restoring user is also the owner of the archived members, and
+that the current @code{umask} is compatible with original permissions.}
+(These parameters will be identical to those which
+the file had when you originally placed it in the archive; any changes
+you may have made before deleting the file from the file system,
+however, will @emph{not} have been made to the archive member.) The
+archive file, @samp{collection.tar}, is the same as it was before you
+extracted @samp{blues}. You can confirm this by running @code{tar} with
+@value{op-list}.
+
+@FIXME{we hope this will change:}Remember that as with other operations,
+specifying the exact member name is important. @w{@kbd{tar --extract
+--file=bfiles.tar birds}} will fail, because there is no member named
+@file{birds}. To extract the member named @file{./birds}, you must
+specify @w{@kbd{tar --extract --file=bfiles.tar ./birds}}. To find the
+exact member names of the members of an archive, use @value{op-list}
+(@pxref{list}).
+
+If you give the @value{op-verbose} option, then @value{op-extract} will
+print the names of the archive members as it extracts them.
+
+@node extract dir, failing commands, extracting files, extract
+@subsection Extracting Files that are Directories
+
+Extracting directories which are members of an archive is similar to
+extracting other files. The main difference to be aware of is that if
+the extracted directory has the same name as any directory already in
+the working directory, then files in the extracted directory will be
+placed into the directory of the same name. Likewise, if there are
+files in the pre-existing directory with the same names as the members
+which you extract, the files from the extracted archive will overwrite
+the files already in the working directory (and possible
+subdirectories). This will happen regardless of whether or not the
+files in the working directory were more recent than those extracted.
+
+However, if a file was stored with a directory name as part of its file
+name, and that directory does not exist under the working directory when
+the file is extracted, @code{tar} will create the directory.
+
+We can demonstrate how to use @samp{--extract} to extract a directory
+file with an example. Change to the @file{practice} directory if you
+weren't there, and remove the files @file{folk} and @file{jazz}. Then,
+go back to the parent directory and extract the archive
+@file{music.tar}. You may either extract the entire archive, or you may
+extract only the files you just deleted. To extract the entire archive,
+don't give any file names as arguments after the archive name
+@file{music.tar}. To extract only the files you deleted, use the
+following command:
@example
-% tar +list -f records
-blues
-folk
-jazz
-rock
-blues
+$ @kbd{tar -xvf music.tar practice/folk practice/jazz}
@end example
-@noindent
-The newest version of @file{blues} is at the end of the archive. When
-the files in @file{records} are extracted, the newer version of
-@file{blues} (which has the same name as the older) will overwrite the
-version stored first. When @samp{tar +extract} is finished, only the
-newer version of @file{blues} is in the file system. <<<xref
-keep-old-files>>>
-
-@node Update, , Append, Adding to Archives
-@subsection Updating Files in an Archive
-
-To keep archive members up to date with their counterparts of the same
-name in the file system, use the @samp{+update} or @samp{-u}
-operation. @samp{tar +update} adds a specified file to an archive if
-no file of that name is already stored in the archive. If there is
-already an archive member with the same name, @code{tar} checks the
-modification date of the archive member, and adds the file only if its
-modification date is later. If a file is stored in the archive but no
-longer exists under the same name in the active file system,
-@code{tar} reports an error.
-
-You could use the @samp{+add-file} option to keep an archive current,
-but do so you would either have to use the @samp{+compare} and
-@samp{+list} options to determine what files needed to be re-archived
-(which could waste a lot of time), or you would have to be willing to
-add identical copies of already archived files to the archive (which
-could waste a lot of space).
-
-You must use file-name arguments with the @samp{+update}
-operation---if you don't specify any files, @code{tar} won't act on
-any files.
-
-To see the @samp{+update} option at work, create a new file,
-@file{~/practice/classical}, and modify the file
-@file{~/practice/blues} (you can use a text editor, such as Emacs, to
-do both these things). Then, with @file{practice} as your working
-directory, invoke @samp{tar +update} using the names of all the files
-in the practice directory as file-name arguments, and specifying the
-@samp{+verbose} option:
-
-@example
-% tar +update +verbose +file=records blues folk rock classical
-blues
-classical
-%
-@end example
+@FIXME{need to show tar's response; used verbose above. also, here's a
+good place to demonstrate the -v -v thing. have to write that up
+(should be trivial, but i'm too tired!).}
@noindent
-Because you specified verbose mode, @code{tar} printed out the names
-of the files it acted on. If you now list the archive members of the
-archive, (@samp{tar +list +file=records}), you will see that the file
-@file{classical} and another version of the file @file{blues} have
-been added to @file{records}.
-
-Note: When you update an archive, @code{tar} does not overwrite old
-archive members when it stores newer versions of a file. This is
-because archive members appear in an archive in the order in which
-they are stored, and some archive devices do not allow writing in the
-middle of an archive.
-
-@node Concatenate, Extracting Files Example, Adding to Archives, Tutorial
-@comment node-name, next, previous, up
-@section Concatenating Archives
-
-To concatenate archive files, use @samp{tar +concatenate} or @samp{tar
--A}. This operation adds other archives to the end of an archive.
-While it may seem intuitive to concatenate archives using @code{cat},
-the utility for adding files together, archive files which have been
-"catted" together cannot be read properly by @code{tar}. Archive
-files incorporate an end of file marker---if archives are concatenated
-using @code{cat}, this marker will appear before the end of the new
-archive. This will interfere with operations on that archive.
-@c <<<xref ignore-zeros>>>
-
-In earlier examples, you stored the @file{~/practice} directory in an
-archive file, @file{~/music}. If you have been following the
-examples, you have since changed the contents of the @file{~/practice}
-directory. There is a current version of the files in the
-@file{practice} directory, however, stored in the archive file
-@file{~/practice/records}.
-
-To store current versions of the files in @file{practice} in the
-archive file @file{music}, you can use @samp{tar +concatenate} to add
-the archive file @file{~/practice/records} to @file{music}. First,
-make sure you are in your home directory (@samp{cd ~}). Then:
+Because you created the directory with @file{practice} as part of the
+file names of each of the files by archiving the @file{practice}
+directory as @file{practice}, you must give @file{practice} as part
+of the file names when you extract those files from the archive.
-@itemize @bullet
-@item
-Invoke @code{tar}, and specify the @samp{+concatenate} operation
-(@samp{-A} or @samp{+concatenate})
+@FIXME{IMPORTANT! show the final structure, here. figure out what it
+will be.}
-@item
-Specify the archive file to be added to
-(@samp{+file=@var{archive-name}} or @samp{-f @var{archive-name}})
+@node failing commands, , extract dir, extract
+@subsection Commands That Will Fail
-@item
-Specify the archives to be added, using file-name arguments. In this
-case, the file-name arguments are, unusually, the names of archive
-files. (Remember to include the path in the archive name, if the
-archive file is not in your working directory.)
-@end itemize
+Here are some sample commands you might try which will not work, and why
+they won't work.
+
+If you try to use this command,
+
+@example
+$ @kbd{tar -xvf music.tar folk jazz}
+@end example
+
+@noindent
+you will get the following response:
@example
-% cd ~
-% tar +concatenate +file=music practice/records
+tar: folk: Not found in archive
+tar: jazz: Not found in archive
+$
@end example
-If you now list the contents of the @file{music}, you see it now
-contains the archive members of @file{practice/records}:
+@noindent
+This is because these files were not originally @emph{in} the parent
+directory @file{..}, where the archive is located; they were in the
+@file{practice} directory, and their file names reflect this:
@example
-%tar +list +file=music
-blues
-folk
-jazz
-rock
-blues
-practice/blues
+$ @kbd{tar -tvf music.tar}
practice/folk
practice/jazz
practice/rock
-practice/blues
-practice/classical
@end example
-@node Deleting Files, , , Tutorial
-@comment node-name, next, previous, up
-@section Deleting Files From an Archive
+@FIXME{make sure the above works when going through the examples in
+order...}
-In some instances, you may want to remove some files from an archive
-stored on disk
+@noindent
+Likewise, if you try to use this command,
-@quotation
-@emph{Caution:} you should never delete files from an archive stored
-on tape---because of the linear nature of tape storage, doing this is
-likely to scramble the archive.
-@end quotation
+@example
+$ @kbd{tar -tvf music.tar folk jazz}
+@end example
-To remove archive members from an archive, use the @samp{+delete}
-operation. You must specify the names of files to be removed as
-file-name arguments. All versions of the named file are removed from
-the archive.
+@noindent
+you would get a similar response. Members with those names are not in the
+archive. You must use the correct member names in order to extract the
+files from the archive.
+
+If you have forgotten the correct names of the files in the archive,
+use @w{@kbd{tar --list --verbose}} to list them correctly.
+
+@FIXME{more examples, here? hag thinks it's a good idea.}
+
+@node going further, , extract, Tutorial
+@section Going Further Ahead in this Manual
+
+@FIXME{need to write up a node here about the things that are going to
+be in the rest of the manual.}
+
+@node tar invocation, operations, Tutorial, Top
+@chapter Invoking GNU @code{tar}
+@UNREVISED
+
+This chapter is about how one invokes the GNU @code{tar} command, from
+the command synopsis (@pxref{Synopsis}). There are numerous options,
+and many styles for writing them. One mandatory option specifies
+the operation @code{tar} should perform (@pxref{Operation Summary}),
+other options are meant to detail how this operation should be performed
+(@pxref{Option Summary}). Non-option arguments are not always interpreted
+the same way, depending on what the operation is.
+
+You will find in this chapter everything about option styles and rules for
+writing them (@pxref{Styles}). On the other hand, operations and options
+are fully described elsewhere, in other chapters. Here, you will find
+only synthetic descriptions for operations and options, together with
+pointers to other parts of the @code{tar} manual.
+
+Some options are so special they are fully described right in this
+chapter. They have the effect of inhibiting the normal operation of
+@code{tar} or else, they globally alter the amount of feedback the user
+receives about what is going on. These are the @value{op-help} and
+@value{op-version} (@pxref{help}), @value{op-verbose} (@pxref{verbose})
+and @value{op-interactive} options (@pxref{interactive}).
-Execution of the @samp{+delete} operation can be very slow.
+@menu
+* Synopsis::
+* using tar options::
+* Styles::
+* All Options::
+* help::
+* verbose::
+* interactive::
+@end menu
-To delete all versions of the file @file{blues} from the archive
-@file{records} in the @file{practice} directory, make sure you are in
-that directory, and then:
+@node Synopsis, using tar options, tar invocation, tar invocation
+@section General Synopsis of @code{tar}
-@itemize @bullet
-@item
-List the contents of the archive file @file{records} (see above for
-the steps involved) to insure that the file(s) you wish to delete are
-stored in the archive. (This step is optional)
+The GNU @code{tar} program is invoked as either one of:
-@item
-Invoke @code{tar} and specify the @samp{+delete} operation
-(@samp{+delete}).
+@example
+@kbd{tar @var{option}@dots{} [@var{name}]@dots{}}
+@kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}}
+@end example
-@item
-Specify the name of the archive file that the file(s) will be deleted
-from (@samp{+file=@var{archive-name}} or @samp{-f @var{archive-name}})
+The second form is for when old options are being used.
+
+You can use @code{tar} to store files in an archive, to extract them from
+an archive, and to do other types of archive manipulation. The primary
+argument to @code{tar}, which is called the @dfn{operation}, specifies
+which action to take. The other arguments to @code{tar} are either
+@dfn{options}, which change the way @code{tar} performs an operation,
+or file names or archive members, which specify the files or members
+@code{tar} is to act on.
+
+You can actually type in arguments in any order, even if in this manual
+the options always precede the other arguments, to make examples easier
+to understand. Further, the option stating the main operation mode
+(the @code{tar} main command) is usually given first.
+
+Each @var{name} in the synopsis above is interpreted as an archive member
+name when the main command is one of @value{op-compare}, @value{op-delete},
+@value{op-extract}, @value{op-list} or @value{op-update}. When naming
+archive members, you must give the exact name of the member in the
+archive, as it is printed by @value{op-list}. For @value{op-append}
+and @value{op-create}, these @var{name} arguments specify the names
+of either files or directory hierarchies to place in the archive.
+These files or hierarchies should already exist in the file system,
+prior to the execution of the @code{tar} command.
-@item
-Specify the files to be deleted, using file-name arguments.
+@code{tar} interprets relative file names as being relative to the
+working directory. @code{tar} will make all file names relative
+(by removing leading slashes when archiving or restoring files),
+unless you specify otherwise (using the @value{op-absolute-names}
+option). @value{xref-absolute-names}, for more information about
+@value{op-absolute-names}.
+
+If you give the name of a directory as either a file name or a member
+name, then @code{tar} acts recursively on all the files and directories
+beneath that directory. For example, the name @file{/} identifies all
+the files in the filesystem to @code{tar}.
+
+The distinction between file names and archive member names is especially
+important when shell globbing is used, and sometimes a source of confusion
+for newcomers. @xref{Wildcards}, for more information about globbing.
+The problem is that shells may only glob using existing files in the
+file system. Only @code{tar} itself may glob on archive members, so when
+needed, you must ensure that wildcard characters reach @code{tar} without
+being interpreted by the shell first. Using a backslash before @samp{*}
+or @samp{?}, or putting the whole argument between quotes, is usually
+sufficient for this.
+
+Even if @var{name}s are often specified on the command line, they
+can also be read from a text file in the file system, using the
+@value{op-files-from} option.
+
+If you don't use any file name arguments, @value{op-append},
+@value{op-delete} and @value{op-concatenate} will do nothing, while
+@value{op-create} will usually yield a diagnostic and inhibit @code{tar}
+execution. The other operations of @code{tar} (@value{op-list},
+@value{op-extract}, @value{op-compare}, and @value{op-update}) will act
+on the entire contents of the archive.
+
+@cindex exit status
+@cindex return status
+Besides successful exits, GNU @code{tar} may fail for many reasons.
+Some reasons correspond to bad usage, that is, when the @code{tar}
+command is improperly written.
+Errors may be encountered later, while encountering an error
+processing the archive or the files. Some errors are recoverable,
+in which case the failure is delayed until @code{tar} has completed
+all its work. Some errors are such that it would not meaningful,
+or at least risky, to continue processing: @code{tar} then aborts
+processing immediately. All abnormal exits, whether immediate or
+delayed, should always be clearly diagnosed on @code{stderr}, after
+a line stating the nature of the error.
+
+GNU @code{tar} returns only a few exit statuses. I'm really
+aiming simplicity in that area, for now. If you are not using the
+@value{op-compare} option, zero means that everything went well, besides
+maybe innocuous warnings. Nonzero means that something went wrong.
+Right now, as of today, ``nonzero'' is almost always 2, except for
+remote operations, where it may be 128.
+
+@node using tar options, Styles, Synopsis, tar invocation
+@section Using @code{tar} Options
+
+GNU @code{tar} has a total of eight operating modes which allow you to
+perform a variety of tasks. You are required to choose one operating
+mode each time you employ the @code{tar} program by specifying one, and
+only one operation as an argument to the @code{tar} command (two lists
+of four operations each may be found at @ref{frequent operations} and
+@ref{Operations}). Depending on circumstances, you may also wish to
+customize how the chosen operating mode behaves. For example, you may
+wish to change the way the output looks, or the format of the files that
+you wish to archive may require you to do something special in order to
+make the archive look right.
+
+You can customize and control @code{tar}'s performance by running
+@code{tar} with one or more options (such as @value{op-verbose}, which
+we used in the tutorial). As we said in the tutorial, @dfn{options} are
+arguments to @code{tar} which are (as their name suggests) optional.
+Depending on the operating mode, you may specify one or more options.
+Different options will have different effects, but in general they all
+change details of the operation, such as archive format, archive name,
+or level of user interaction. Some options make sense with all
+operating modes, while others are meaningful only with particular modes.
+You will likely use some options frequently, while you will only use
+others infrequently, or not at all. (A full list of options is
+available in @pxref{All Options}.)
+
+Note that @code{tar} options are case sensitive. For example, the
+options @samp{-T} and @samp{-t} are different; the first requires an
+argument for stating the name of a file providing a list of @var{name}s,
+while the second does not require an argument and is another way to
+write @value{op-list}.
+
+In addition to the eight operations, there are many options to
+@code{tar}, and three different styles for writing both: long (mnemonic)
+form, short form, and old style. These styles are discussed below.
+Both the options and the operations can be written in any of these three
+styles.
+
+@FIXME{menu at end of this node. need to think of an actual outline
+for this chapter; probably do that after stuff from chap. 4 is
+incorporated.}
+
+@node Styles, All Options, using tar options, tar invocation
+@section The Three Option Styles
+
+There are three styles for writing operations and options to the command
+line invoking @code{tar}. The different styles were developed at
+different times during the history of @code{tar}. These styles will be
+presented below, from the most recent to the oldest.
+
+Some options must take an argument. (For example, @value{op-file} takes
+the name of an archive file as an argument. If you do not supply an
+archive file name, @code{tar} will use a default, but this can be
+confusing; thus, we recommend that you always supply a specific archive
+file name.) Where you @emph{place} the arguments generally depends on
+which style of options you choose. We will detail specific information
+relevant to each option style in the sections on the different option
+styles, below. The differences are subtle, yet can often be very
+important; incorrect option placement can cause you to overwrite a
+number of important files. We urge you to note these differences, and
+only use the option style(s) which makes the most sense to you until you
+feel comfortable with the others.
+
+@FIXME{hag to write a brief paragraph on the option(s) which can
+optionally take an argument}
-@item
-List the contents of the archive file again---note that the files have
-been removed. (this step is also optional)
-@end itemize
+@menu
+* Mnemonic Options:: Mnemonic Option Style
+* Short Options:: Short Option Style
+* Old Options:: Old Option Style
+* Mixing:: Mixing Option Styles
+@end menu
+
+@node Mnemonic Options, Short Options, Styles, Styles
+@subsection Mnemonic Option Style
+
+@FIXME{have to decide whether or ot to replace other occurrences of
+"mnemonic" with "long", or *ugh* vice versa.}
+
+Each option has at least one long (or mnemonic) name starting with two
+dashes in a row, e.g. @samp{list}. The long names are more clear than
+their corresponding short or old names. It sometimes happens that a
+single mnemonic option has many different different names which are
+synonymous, such as @samp{--compare} and @samp{--diff}. In addition,
+long option names can be given unique abbreviations. For example,
+@samp{--cre} can be used in place of @samp{--create} because there is no
+other mnemonic option which begins with @samp{cre}. (One way to find
+this out is by trying it and seeing what happens; if a particular
+abbreviation could represent more than one option, @code{tar} will tell
+you that that abbreviation is ambiguous and you'll know that that
+abbreviation won't work. You may also choose to run @samp{tar --help}
+to see a list of options. Be aware that if you run @code{tar} with a
+unique abbreviation for the long name of an option you didn't want to
+use, you are stuck; @code{tar} will perform the command as ordered.)
+
+Mnemonic options are meant to be obvious and easy to remember, and their
+meanings are generally easier to discern than those of their
+corresponding short options (see below). For example:
@example
-% tar +list +file=records
-blues
-folk
-jazz
-% tar +delete +file=records blues
-% tar +list +file=records
-folk
-jazz
-%
+$ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0}
+@end example
+
+@noindent
+gives a fairly good set of hints about what the command does, even
+for those not fully acquainted with @code{tar}.
+
+Mnemonic options which require arguments take those arguments
+immediately following the option name; they are introduced by an equal
+sign. For example, the @samp{--file} option (which tells the name
+of the @code{tar} archive) is given a file such as @file{archive.tar}
+as argument by using the notation @samp{--file=archive.tar} for the
+mnemonic option.
+
+@node Short Options, Old Options, Mnemonic Options, Styles
+@subsection Short Option Style
+
+Most options also have a short option name. Short options start with
+a single dash, and are followed by a single character, e.g. @samp{-t}
+(which is equivalent to @samp{--list}). The forms are absolutely
+identical in function; they are interchangeable.
+
+The short option names are faster to type than long option names.
+
+Short options which require arguments take their arguments immediately
+following the option, usually separated by white space. It is also
+possible to stick the argument right after the short option name, using
+no intervening space. For example, you might write @w{@samp{-f
+archive.tar}} or @samp{-farchive.tar} instead of using
+@samp{--file=archive.tar}. Both @samp{--file=@var{archive-name}} and
+@w{@samp{-f @var{archive-name}}} denote the option which indicates a
+specific archive, here named @file{archive.tar}.
+
+Short options' letters may be clumped together, but you are not
+required to do this (as compared to old options; see below). When short
+options are clumped as a set, use one (single) dash for them all, e.g.
+@w{@samp{@code{tar} -cvf}}. Only the last option in such a set is allowed
+to have an argument@footnote{Clustering many options, the last of which
+has an argument, is a rather opaque way to write options. Some wonder if
+GNU @code{getopt} should not even be made helpful enough for considering
+such usages as invalid.}.
+
+When the options are separated, the argument for each option which requires
+an argument directly follows that option, as is usual for Unix programs.
+For example:
+
+@example
+$ @kbd{tar -c -v -b 20 -f /dev/rmt0}
@end example
-@node Wizardry, Archive Structure, Tutorial, Top
-@chapter Wizardry
+If you reorder short options' locations, be sure to move any arguments
+that belong to them. If you do not move the arguments properly, you may
+end up overwriting files.
+
+@node Old Options, Mixing, Short Options, Styles
+@subsection Old Option Style
+@UNREVISED
+
+Like short options, old options are single letters. However, old options
+must be written together as a single clumped set, without spaces separating
+them or dashes preceding them@footnote{Beware that if you precede options
+with a dash, you are announcing the short option style instead of the
+old option style; short options are decoded differently.}. This set
+of letters must be the first to appear on the command line, after the
+@code{tar} program name and some whitespace; old options cannot appear
+anywhere else. The letter of an old option is exactly the same letter as
+the corresponding short option. For example, the old option @samp{t} is
+the same as the short option @samp{-t}, and consequently, the same as the
+mnemonic option @samp{--list}. So for example, the command @w{@samp{tar
+cv}} specifies the option @samp{-v} in addition to the operation @samp{-c}.
+
+@FIXME{bob suggests having an uglier example. :-) }
+
+When options that need arguments are given together with the command,
+all the associated arguments follow, in the same order as the options.
+Thus, the example given previously could also be written in the old
+style as follows:
-<<<This section needs to be written -ringo
+@example
+$ @kbd{tar cvbf 20 /dev/rmt0}
+@end example
-@strong{To come:} using Unix file linking capability to recreate directory
-structures---linking files into one subdirectory and then tarring that
-directory.
+@noindent
+Here, @samp{20} is the argument of @samp{-b} and @samp{/dev/rmt0} is
+the argument of @samp{-f}.
-@strong{to come:} nice hairy example using absolute-paths, newer, etc.
+On the other hand, this old style syntax makes it difficult to match
+option letters with their corresponding arguments, and is often
+confusing. In the command @w{@samp{tar cvbf 20 /dev/rmt0}}, for example,
+@samp{20} is the argument for @samp{-b}, @samp{/dev/rmt0} is the
+argument for @samp{-f}, and @samp{-v} does not have a corresponding
+argument. Even using short options like in @w{@samp{tar -c -v -b 20 -f
+/dev/rmt0}} is clearer, putting all arguments next to the option they
+pertain to.
+If you want to reorder the letters in the old option argument, be
+sure to reorder any corresponding argument appropriately.
-Piping one @code{tar} to another is an easy way to copy a directory's
-contents from one disk to another, while preserving the dates, modes, owners
-and link-structure of all the files therein.
+This old way of writing @code{tar} options can surprise even experienced
+users. For example, the two commands:
@example
-cd sourcedirectory; tar cf - . | (cd targetdir; tar xf -)
+@kbd{tar cfz archive.tar.gz file}
+@kbd{tar -cfz archive.tar.gz file}
@end example
@noindent
-or
+are quite different. The first example uses @file{archive.tar.gz} as
+the value for option @samp{f} and recognizes the option @samp{z}. The
+second example, however, uses @file{z} as the value for option
+@samp{f}---probably not what was intended.
+
+Old options are kept for compatibility with old versions of @code{tar}.
+
+This second example could be corrected in many ways, among which the
+following are equivalent:
-<<< the following using standard input/output correct??
@example
-cd sourcedirectory; tar +create +file=- . | (cd targetdir; tar +extract +file=-)
+@kbd{tar -czf archive.tar.gz file}
+@kbd{tar -cf archive.tar.gz -z file}
+@kbd{tar cf archive.tar.gz -z file}
@end example
-@noindent
+@FIXME{still could explain this better; it's redundant:}
-Archive files can be used for transporting a group of files from one system
-to another: put all relevant files into an archive on one computer system,
-transfer the archive to another, and extract the contents there. The basic
-transfer medium might be magnetic tape, Internet FTP, or even electronic
-mail (though you must encode the archive with @code{uuencode} in order to
-transport it properly by mail). Both machines do not have to use the same
-operating system, as long as they both support the @code{tar} program.
-@findex uuencode
-<<< mention uuencode on a paragraph of its own
+@cindex option syntax, traditional
+As far as we know, all @code{tar} programs, GNU and non-GNU, support
+old options. GNU @code{tar} supports them not only for historical
+reasons, but also because many people are used to them. For
+compatibility with Unix @code{tar}, the first argument is always
+treated as containing command and option letters even if it doesn't
+start with @samp{-}. Thus, @samp{tar c} is equivalent to @w{@samp{tar
+-c}:} both of them specify the @value{op-create} command to create an
+archive.
-<<<<<end construction>>>>>
+@node Mixing, , Old Options, Styles
+@subsection Mixing Option Styles
-@node Archive Structure, Reading and Writing, Wizardry, Top
-@chapter The Structure of an Archive
+All three styles may be intermixed in a single @code{tar} command, so
+long as the rules for each style are fully respected@footnote{Before GNU
+@code{tar} version 1.11.6, a bug prevented intermixing old style options
+with mnemonic options in some cases.}. Old style options and either of the
+modern styles of options may be mixed within a single @code{tar} command.
+However, old style options must be introduced as the first arguments only,
+following the rule for old options (old options must appear directly
+after the @code{tar} command and some whitespace). Modern options may
+be given only after all arguments to the old options have been collected.
+If this rule is not respected, a modern option might be falsely interpreted
+as the value of the argument to one of the old style options.
-While an archive may contain many files, the archive itself is a
-single ordinary file. Like any other file, an archive file can be
-written to a storage device such as a tape or disk, sent through a
-pipe or over a network, saved on the active file system, or even
-stored in another archive. An archive file is not easy to read or
-manipulate without using the @code{tar} utility or Tar mode in Emacs.
+For example, all the following commands are wholly equivalent, and
+illustrate the many combinations and orderings of option styles.
+@example
+@kbd{tar --create --file=archive.tar}
+@kbd{tar --create -f archive.tar}
+@kbd{tar --create -farchive.tar}
+@kbd{tar --file=archive.tar --create}
+@kbd{tar --file=archive.tar -c}
+@kbd{tar -c --file=archive.tar}
+@kbd{tar -c -f archive.tar}
+@kbd{tar -c -farchive.tar}
+@kbd{tar -cf archive.tar}
+@kbd{tar -cfarchive.tar}
+@kbd{tar -f archive.tar --create}
+@kbd{tar -f archive.tar -c}
+@kbd{tar -farchive.tar --create}
+@kbd{tar -farchive.tar -c}
+@kbd{tar c --file=archive.tar}
+@kbd{tar c -f archive.tar}
+@kbd{tar c -farchive.tar}
+@kbd{tar cf archive.tar}
+@kbd{tar f archive.tar --create}
+@kbd{tar f archive.tar -c}
+@kbd{tar fc archive.tar}
+@end example
-Physically, an archive consists of a series of file entries terminated
-by an end-of-archive entry, which consists of 512 zero bytes. A file
-entry usually describes one of the files in the archive (an
-@dfn{archive member}), and consists of a file header and the contents
-of the file. File headers contain file names and statistics, checksum
-information which @code{tar} uses to detect file corruption, and
-information about file types.
+On the other hand, the following commands are @emph{not} equivalent to
+the previous set:
-More than archive member can have the same file name. One way this
-situation can occur is if more than one version of a file has been
-stored in the archive. For information about adding new versions of a
-file to an archive, @pxref{Modifying}.
+@example
+@kbd{tar -f -c archive.tar}
+@kbd{tar -fc archive.tar}
+@kbd{tar -fcarchive.tar}
+@kbd{tar -farchive.tarc}
+@kbd{tar cfarchive.tar}
+@end example
-In addition to entries describing archive members, an archive may contain
-entries which @code{tar} itself uses to store information.
-@xref{Archive Label}, for an example of such an archive entry.
+@noindent
+These last examples mean something completely different from what the
+user intended (judging based on the example in the previous set which
+uses long options, whose intent is therefore very clear). The first
+four specify that the @code{tar} archive would be a file named
+@samp{-c}, @samp{c}, @samp{carchive.tar} or @samp{archive.tarc},
+respectively. The first two examples also specify a single non-option,
+@var{name} argument having the value @samp{archive.tar}. The last
+example contains only old style option letters (repeating option
+@samp{c} twice), not all of which are meaningful (eg., @samp{.},
+@samp{h}, or @samp{i}), with no argument value. @FIXME{not sure i liked
+the first sentence of this paragraph..}
+
+@node All Options, help, Styles, tar invocation
+@section All @code{tar} Options
+
+The coming manual sections contain an alphabetical listing of all
+@code{tar} operations and options, with brief descriptions and cross
+references to more in-depth explanations in the body of the manual.
+They also contain an alphabetically arranged table of the short option
+forms with their corresponding long option. You can use this table as
+a reference for deciphering @code{tar} commands in scripts.
@menu
-* Old Style File Information:: Old Style File Information
-* Archive Label::
-* Format Variations::
+* Operation Summary::
+* Option Summary::
+* Short Option Summary::
@end menu
-@node Old Style File Information, Archive Label, Archive Structure, Archive Structure
-@section Old Style File Information
-@cindex Format, old style
-@cindex Old style format
-@cindex Old style archives
-
-Archives record not only an archive member's contents, but also its
-file name or names, its access permissions, user and group, size in
-bytes, and last modification time. Some archives also record the file
-names in each archived directory, as well as other file and directory
-information.
+@node Operation Summary, Option Summary, All Options, All Options
+@subsection Operations
-Certain old versions of @code{tar} cannot handle additional
-information recorded by newer @code{tar} programs. To create an
-archive which can be read by these old versions, specify the
-@samp{+old-archive} option in conjunction with the @samp{tar +create}
-operation. When you specify this option, @code{tar} leaves out
-information about directories, pipes, fifos, contiguous files, and
-device files, and specifies file ownership by group and user ids
-instead of names.
-
-The @samp{+old-archive} option is needed only if the archive must be
-readable by an older tape archive program which cannot handle the new format.
-Most @code{tar} programs do not have this limitation, so this option
-is seldom needed.
+@table @kbd
-@table @samp
-@item +old-archive
-@itemx -o
-@itemx +old
-@itemx +portable
-@c has portability been changed to portable?
-Creates an archive that can be read by an old @code{tar} program.
-Used in conjunction with the @samp{tar +create} operation.
-@end table
+@item --append
+@itemx -r
-@node Archive Label, Format Variations, Old Style File Information, Archive Structure
-@section Including a Label in the Archive
-@cindex Labeling an archive
-@cindex Labels on the archive media
+Appends files to the end of the archive. @xref{append}.
-@c !! Should the arg to +label be a quoted string?? no - ringo
-To avoid problems caused by misplaced paper labels on the archive
-media, you can include a @dfn{label} entry---an archive member which
-contains the name of the archive---in the archive itself. Use the
-@samp{+label=@var{archive-label}} option in conjunction with the
-@samp{+create} operation to include a label entry in the archive as it
-is being created.
+@item --catenate
+@itemx -A
-If you create an archive using both @samp{+label=@var{archive-label}}
-and @samp{+multi-volume}, each volume of the archive will have an
-archive label of the form @samp{@var{archive-label} Volume @var{n}},
-where @var{n} is 1 for the first volume, 2 for the next, and so on.
-@xref{Multi-Volume Archives}, for information on creating multiple
-volume archives.
+Same as @samp{--concatenate}. @xref{concatenate}.
-If you extract an archive using @samp{+label=@var{archive-label}},
-@code{tar} will print an error if the archive label doesn't match the
-@var{archive-label} specified, and will then not extract the archive.
-You can include a regular expression in @var{archive-label}, in this
-case only.
-@c >>> why is a reg. exp. useful here? (to limit extraction to a
-@c >>>specific group? ie for multi-volume??? -ringo
+@item --compare
+@itemx -d
-To find out an archive's label entry (or to find out if an archive has
-a label at all), use @samp{tar +list +verbose}. @code{tar} will print the
-label first, and then print archive member information, as in the
-example below:
+Compares archive members with their counterparts in the file
+system, and reports differences in file size, mode, owner,
+modification date and contents. @xref{compare}.
-@example
-% tar +verbose +list +file=iamanarchive
-V--------- 0/0 0 Mar 7 12:01 1992 iamalabel--Volume Header--
--rw-rw-rw- ringo/user 40 May 21 13:30 1990 iamafilename
-@end example
+@item --concatenate
+@itemx -A
-@table @samp
-@item +label=@var{archive-label}
-@itemx -V @var{archive-label}
-Includes an @dfn{archive-label} at the beginning of the archive when
-the archive is being created (when used in conjunction with the
-@samp{tar +create} operation). Checks to make sure the archive label
-matches the one specified (when used in conjunction with the @samp{tar
-+extract} operation.
-@end table
-@c was +volume
+Appends other @code{tar} archives to the end of the archive.
+@xref{concatenate}.
-@node Format Variations, , Archive Label, Archive Structure
-@section Format Variations
-@cindex Format Parameters
-@cindex Format Options
-@cindex Options to specify archive format.
+@item --create
+@itemx -c
-Format parameters specify how an archive is written on the archive
-media. The best choice of format parameters will vary depending on
-the type and number of files being archived, and on the media used to
-store the archive.
+Creates a new @code{tar} archive. @xref{create}.
-To specify format parameters when accessing or creating an archive,
-you can use the options described in the following sections. If you
-do not specify any format parameters, @code{tar} uses default
-parameters. You cannot modify a compressed archive. If you create an
-archive with the @samp{+block-size} option specified (@pxref{Blocking
-Factor}), you must specify that block-size when operating on the
-archive. @xref{Matching Format Parameters}, for other examples of
-format parameter considerations.
+@item --delete
+Deletes members from the archive. Don't try this on a archive on a
+tape! @xref{delete}.
-@menu
-* Multi-Volume Archives::
-* Sparse Files::
-* Blocking Factor::
-* Compressed Archives::
-@end menu
+@item --diff
+@itemx -d
-@node Multi-Volume Archives, Sparse Files, Format Variations, Format Variations
-@subsection Archives Longer than One Tape or Disk
-@cindex Multi-volume archives
+Same @samp{--compare}. @xref{compare}.
-To create an archive that is larger than will fit on a single unit of
-the media, use the @samp{+multi-volume} option in conjunction with the
-@samp{tar +create} operation (@pxref{Creating Archives}). A
-@dfn{multi-volume} archive can be manipulated like any other archive
-(provided the @samp{+multi-volume} option is specified), but is stored
-on more than one tape or disk.
+@item --extract
+@itemx -x
-When you specify @samp{+multi-volume}, @code{tar} does not report an
-error when it comes to the end of an archive volume (when reading), or
-the end of the media (when writing). Instead, it prompts you to load
-a new storage volume. If the archive is on a magnetic tape, you
-should change tapes when you see the prompt; if the archive is on a
-floppy disk, you should change disks; etc.
+Extracts members from the archive into the file system. @xref{extract}.
-You can read each individual volume of a multi-volume archive as if it
-were an archive by itself. For example, to list the contents of one
-volume, use @samp{tar +list}, without @samp{+multi-volume} specified.
-To extract an archive member from one volume (assuming it is described
-that volume), use @samp{tar +extract}, again without
-@samp{+multi-volume}.
+@item --get
+@itemx -x
-If an archive member is split across volumes (ie. its entry begins on
-one volume of the media and ends on another), you need to specify
-@samp{+multi-volume} to extract it successfully. In this case, you
-should load the volume where the archive member starts, and use
-@samp{tar +extract +multi-volume}---@code{tar} will prompt for later
-volumes as it needs them. @xref{Extracting From Archives} for more
-information about extracting archives.
+Same as @samp{--extract}. @xref{extract}.
-@samp{+info-script=@var{program-file}} is like @samp{+multi-volume},
-except that @code{tar} does not prompt you directly to change media
-volumes when a volume is full---instead, @code{tar} runs commands you
-have stored in @var{program-file}. This option can be used to
-broadcast messages such as @samp{someone please come change my tape}
-when performing unattended backups. When @var{program-file} is done,
-@code{tar} will assume that the media has been changed.
+@item --list
+@itemx -t
+Lists the members in an archive. @xref{list}.
-<<< There should be a sample program here, including an exit before
-<<< end.
+@item --update
+@itemx -u
-@table @samp
-@item +multi-volume
-@itemx -M
-Creates a multi-volume archive, when used in conjunction with
-@samp{tar +create}. To perform any other operation on a multi-volume
-archive, specify @samp{+multi-volume} in conjunction with that
-operation.
+@FIXME{It was: A combination of the @samp{--compare} and @samp{--append} operations.
+This is not true and rather misleading, as @value{op-compare}
+does a lot more than @value{op-update} for ensuring files are identical.}
+Adds files to the end of the archive, but only if they are newer than
+their counterparts already in the archive, or if they do not already
+exist in the archive.
+@xref{update}.
-@item +info-script=@var{program-file}
-@itemx -F @var{program-file}
-Creates a multi-volume archive via a script. Used in conjunction with
-@samp{tar +create}.
@end table
-@node Sparse Files, Blocking Factor, Multi-Volume Archives, Format Variations
-@subsection Archiving Sparse Files
-@cindex Sparse Files
+@node Option Summary, Short Option Summary, Operation Summary, All Options
+@subsection @code{tar} Options
-A file is sparse if it contains blocks of zeros whose existance is
-recorded, but that have no space allocated on disk. When you specify
-the @samp{+sparse} option in conjunction with the @samp{+create}
-operation, @code{tar} tests all files for sparseness while archiving.
-If @code{tar} finds a file to be sparse, it uses a sparse
-representation of the file in the archive. @xref{Creating Archives},
-for more information about creating archives.
+@table @kbd
-@samp{+sparse} is useful when archiving files, such as dbm files,
-likely to contain many nulls. This option dramatically
-decreases the amount of space needed to store such an archive.
+@item --absolute-names
+@itemx -P
-@quotation
-@strong{Please Note:} Always use @samp{+sparse} when performing file
-system backups, to avoid archiving the expanded forms of files stored
-sparsely in the system.@refill
+Normally when creating an archive, @code{tar} strips an initial @samp{/} from
+member names. This option disables that behavior. @FIXME-xref{}.
-Even if your system has no no sparse files currently, some may be
-created in the future. If you use @samp{+sparse} while making file
-system backups as a matter of course, you can be assured the archive
-will always take no more space on the media than the files take on
-disk (otherwise, archiving a disk filled with sparse files might take
-hundreds of tapes).@refill
-<<< xref incremental when node name is set.
-@end quotation
+@item --after-date
-@code{tar} ignores the @samp{+sparse} option when reading an archive.
+(See @samp{--newer}; @FIXME-pxref{}.)
-@table @samp
-@item +sparse
-@itemx -S
-Files stored sparsely in the file system are represented sparsely in
-the archive. Use in conjunction with write operations.
-@end table
+@item --atime-preserve
-@node Blocking Factor, Compressed Archives, Sparse Files, Format Variations
-@subsection The Blocking Factor of an Archive
-@cindex Blocking Factor
-@cindex Block Size
-@cindex Number of records per block
-@cindex Number of bytes per block
-@cindex Bytes per block
-@cindex Records per block
-
-The data in an archive is grouped into records, which are 512 bytes.
-Records are read and written in whole number multiples called
-@dfn{blocks}. The number of records in a block (ie. the size of a
-block in units of 512 bytes) is called the @dfn{blocking factor}. The
-@samp{+block-size=@var{number}} option specifies the blocking factor
-of an archive. The default blocking factor is typically 20 (ie.@:
-10240 bytes), but can be specified at installation. To find out the
-blocking factor of an existing archive, use @samp {tar +list
-+file=@var{archive-name}}. This may not work on some devices.
-
-Blocks are seperated by gaps, which waste space on the archive media.
-If you are archiving on magnetic tape, using a larger blocking factor
-(and therefore larger blocks) provides faster throughput and allows
-you to fit more data on a tape (because there are fewer gaps). If you
-are archiving on cartridge, a very large blocking factor (say 126 or
-more) greatly increases performance. A
-smaller blocking factor, on the other hand, may be usefull when
-archiving small files, to avoid archiving lots of nulls as @code{tar}
-fills out the archive to the end of the block. In general, the ideal block size
-depends on the size of the inter-block gaps on the tape you are using,
-and the average size of the files you are archiving. @xref{Creating
-Archives}, for information on writing archives.
-
-Archives with blocking factors larger than 20 cannot be read by very
-old versions of @code{tar}, or by some newer versions of @code{tar}
-running on old machines with small address spaces. With GNU
-@code{tar}, the blocking factor of an archive is limited only by the
-maximum block size of the device containing the archive, or by the
-amount of available virtual memory.
-
-If you use a non-default blocking factor when you create an archive,
-you must specify the same blocking factor when you modify that
-archive. Some archive devices will also require you to specify the
-blocking factor when reading that archive, however this is not
-typically the case. Usually, you can use @samp{tar +list} without
-specifying a blocking factor---@code{tar} reports a non-default block
-size and then lists the archive members as it would normally. To
-extract files from an archive with a non-standard blocking factor
-(particularly if you're not sure what the blocking factor is), you can
-usually use the {+read-full-blocks} option while specifying a blocking
-factor larger then the blocking factor of the archive (ie. @samp{tar
-+extract +read-full-blocks +block-size=300}. @xref{Listing Contents}
-for more information on the @samp{+list} operation.
-@xref{read-full-blocks} for a more detailed explanation of that
-option.
+Tells @code{tar} to preserve the access time field in a file's inode when
+dumping it. @FIXME-xref{}.
-@table @samp
-@item +block-size=@var{number}
-@itemx -b @var{number}
-Specifies the blocking factor of an archive. Can be used with any
-operation, but is usually not necessary with @samp{tar +list}.
-@end table
+@item --backup=@var{backup-type}
-@node Compressed Archives, , Blocking Factor, Format Variations
-@subsection Creating and Reading Compressed Archives
-@cindex Compressed archives
-@cindex Storing archives in compressed format
+Rather than deleting files from the file system, @code{tar} will back them up
+using simple or numbered backups, depending upon @var{backup-type}.
+@FIXME-xref{}.
-@samp{+compress} indicates an archive stored in compressed format.
-The @samp{+compress} option is useful in saving time over networks and
-space in pipes, and when storage space is at a premium.
-@samp{+compress} causes @code{tar} to compress when writing the
-archive, or to uncompress when reading the archive.
+@item --block-number
+@itemx -R
-To perform compression and uncompression on the archive, @code{tar}
-runs the @code{compress} utility. @code{tar} uses the default
-compression parameters; if you need to override them, avoid the
-@samp{+compress} option and run the @code{compress} utility
-explicitly. It is useful to be able to call the @code{compress}
-utility from within @code{tar} because the @code{compress} utility by
-itself cannot access remote tape drives.
+With this option present, @code{tar} prints error messages for read errors
+with the block number in the archive file. @FIXME-xref{}.
-The @samp{+compress} option will not work in conjunction with the
-@samp{+multi-volume} option or the @samp{+add-file}, @samp{+update},
-@samp{+add-file} and @samp{+delete} operations. @xref{Modifying}, for
-more information on these operations.
+@item --blocking-factor=@var{blocking}
+@itemx -b @var{blocking}
-If there is no compress utility available, @code{tar} will report an
-error.
+Sets the blocking factor @code{tar} uses to @var{blocking} x 512 bytes per
+record. @FIXME-xref{}.
-@samp{+compress-block} is like @samp{+compress}, but when used in
-conjunction with @samp{+create} also causes @code{tar} to pad the last
-block of the archive out to the next block boundary as it is written.
-This is useful with certain devices which require all write operations
-be a multiple of a specific size.
+@item --checkpoint
-@quotation
-@strong{Please Note:} The @code{compress} program may be covered by a patent,
-and therefore we recommend you stop using it. We hope to have a
-different compress program in the future. We may change the name of
-this option at that time.
-@end quotation
+This option directs @code{tar} to print periodic checkpoint messages as it
+reads through the archive. Its intended for when you want a visual
+indication that @code{tar} is still running, but don't want to see
+@samp{--verbose} output. @FIXME-xref{}.
-@table @samp
-@item +compress
-@itemx +uncompress
-@itemx -z
+@item --compress
+@itemx --uncompress
@itemx -Z
-When this option is specified, @code{tar} will compress (when writing
-an archive), or uncompress (when reading an archive). Used in
-conjunction with the @samp{+create}, @samp{+extract}, @samp{+list} and
-@samp{+compare} operations.
-
-@item +compress-block
-@itemx -z -z
-Acts like @samp{+compress}, but pads the archive out to the next block
-boundary as it is written when used in conjunction with the
-@samp{+create} operation.
-@end table
-@c >>> MIB -- why not use -Z instead of -z -z ? -ringo
+@code{tar} will use the @code{compress} program when reading or writing the
+archive. This allows you to directly act on archives while saving
+space. @FIXME-xref{}.
-@node Reading and Writing, Insuring Accuracy, Archive Structure, Top
-@chapter Reading and Writing Archives
+@item --confirmation
-The @samp{+create} operation writes a new archive, and the
-@samp{+extract} operation reads files from an archive and writes them
-into the file system. You can use other @code{tar} operations to
-write new information into an existing archive (adding files to it,
-adding another archive to it, or deleting files from it), and you can
-read a list of the files in an archive without extracting it using the
-@samp{+list} operation.
+(See @samp{--interactive}; @FIXME-pxref{}.)
-@menu
-* Archive Name:: The name of an archive
-* Creating in Detail:: Creating in detail
-* Modifying:: Modifying archives
-* Listing Contents:: Listing the contents of an archive
-* Extracting From Archives:: Extracting files from an archive
-@end menu
+@item --dereference
+@itemx -h
-@node Archive Name, Creating in Detail, Reading and Writing, Reading and Writing
-@section The Name of an Archive
-@cindex Naming an archive
-@cindex Archive Name
-@cindex Directing output
-@cindex Where is the archive?
+When creating a @code{tar} archive, @code{tar} will archive the file that a symbolic
+link points to, rather than archiving the symlink. @FIXME-xref{}.
-An archive can be saved as a file in the file system, sent through a
-pipe or over a network, or written to an I/O device such as a tape or
-disk drive. To specify the name of the archive, use the
-@samp{+file=@var{archive-name}} option.
+@item --directory=@var{dir}
+@itemx -C @var{dir}
-An archive name can be the name of an ordinary file or the name of an
-I/O device. @code{tar} always needs an archive name---if you do not
-specify an archive name, the archive name comes from the environment
-variable @code{TAPE} or, if that variable is not specified, a default
-archive name, which is usually the name of tape unit zero (ie.
-/dev/tu00).
+When this option is specified, @code{tar} will change its current directory
+to @var{dir} before performing any operations. When this option is used
+during archive creation, it is order sensitive. @FIXME-xref{}.
-If you use @file{-} as an @var{archive-name}, @code{tar} reads the
-archive from standard input (when listing or extracting files), or
-writes it to standard output (when creating an archive). If you use
-@file{-} as an @var{archive-name} when modifying an archive,
-@code{tar} reads the original archive from its standard input and
-writes the entire new archive to its standard output.
+@item --exclude=@var{pattern}
-@c >>> MIB--does standard input and output redirection work with all
-@c >>> operations?
-@c >>> need example for standard input and output (screen and keyboard?)
+When performing operations, @code{tar} will skip files that match
+@var{pattern}. @FIXME-xref{}.
-@cindex Standard input and output
-@cindex tar to standard input and output
+@item --exclude-from=@var{file}
+@itemx -X @var{file}
-To specify an archive file on a device attached to a remote machine,
-use the following:
+Similar to @samp{--exclude}, except @code{tar} will use the list of patterns
+in the file @var{file}. @FIXME-xref{}.
-@example
-+file=@var{hostname}:/@var{dev}/@var{file name}
-@end example
+@item --file=@var{archive}
+@itemx -f @var{archive}
-@noindent
-@code{tar} will complete the remote connection, if possible, and
-prompt you for a username and password. If you use
-@samp{+file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @code{tar}
-will complete the remote connection, if possible, using your username
-as the username on the remote machine.
+@code{tar} will use the file @var{archive} as the @code{tar} archive it
+performs operations on, rather than @code{tar}'s compilation dependent
+default. @FIXME-xref{}.
-@c >>>MIB --- is this clear?
+@item --files-from=@var{file}
+@itemx -T @var{file}
-@table @samp
-@item +file=@var{archive-name}
-@itemx -f @var{archive-name}
-Names the archive to create or operate on. Use in conjunction with
-any operation.
-@end table
+@code{tar} will use the contents of @var{file} as a list of archive members
+or files to operate on, in addition to those specified on the
+command-line. @FIXME-xref{}.
-@node Creating in Detail, Modifying, Archive Name, Reading and Writing
-@section Creating in Detail
-@c operations should probably have examples, not tables.
-@cindex Writing new archives
-@cindex Archive creation
+@item --force-local
-To create an archive, use @samp{tar +create}. To name the archive,
-use @samp{+file=@var{archive-name}} in conjunction with the
-@samp{+create} operation (@pxref{Archive Name}). If you do not name
-the archive, @code{tar} uses the value of the environment variable
-@code{TAPE} as the file name for the archive, or, if that is not
-available, @code{tar} uses a default archive name, usually that for tape
-unit zero. @xref{Archive Name}, for more information about specifying
-an archive name.
+Forces @code{tar} to interpret the filename given to @samp{--file} as a local
+file, even if it looks like a remote tape drive name. @FIXME-xref{}.
-The following example creates an archive named @file{stooges},
-containing the files @file{larry}, @file{moe} and @file{curley}:
+@item --group=@var{group}
-@example
-tar +create +file=stooges larry moe curley
-@end example
+Files added to the @code{tar} archive will have a group id of @var{group},
+rather than the group from the source file. @var{group} is first decoded
+as a group symbolic name, but if this interpretation fails, it has to be
+a decimal numeric group ID. @FIXME-xref{}.
-If you specify a directory name as a file-name argument, @code{tar}
-will archive all the files in that directory. The following example
-creates an archive named @file{hail/hail/fredonia}, containing the
-contents of the directory @file{marx}:
+Also see the comments for the @value{op-owner} option.
-@example
-tar +create +file=hail/hail/fredonia marx
-@end example
+@item --gunzip
-If you don't specify files to put in the archive, @code{tar} archives
-all the files in the working directory. The following example creates
-an archive named @file{home} containing all the files in the working
-directory:
+(See @samp{--gzip}; @FIXME-pxref{}.)
-@example
-tar +create +file=home
-@end example
+@item --gzip
+@itemx --gunzip
+@itemx --ungzip
+@itemx -z
-@xref{File Name Lists}, for other ways to specify files to archive.
+This option tells @code{tar} to read or write archives through @code{gzip},
+allowing @code{tar} to directly operate on several kinds of compressed
+archives transparently. @FIXME-xref{}.
-Note: In the example above, an archive containing all the files in the
-working directory is being written to the working directory. GNU
-@code{tar} stores files in the working directory in an archive which
-is itself in the working directory without falling into an infinite
-loop. Other versions of @code{tar} may fall into this trap.
+@item --help
-@node Modifying, Listing Contents, Creating in Detail, Reading and Writing
-@section Modifying Archives
-@cindex Modifying archives
+@code{tar} will print out a short message summarizing the operations and
+options to @code{tar} and exit. @FIXME-xref{}.
-Once an archive is created, you can add new archive members to it, add
-the contents of another archive, add newer versions of members already
-stored, or delete archive members already stored.
+@item --ignore-failed-read
-To find out what files are already stored in an archive, use @samp{tar
-+list +file=@var{archive-name}}. @xref{Listing Contents}.
+Instructs @code{tar} to exit successfully if it encounters an
+unreadable file. @xref{Reading}.
-@menu
-* Adding Files::
-* Appending Archives::
-* Deleting Archive Files:: Deleting Files From an Archive
-* Matching Format Parameters::
-@end menu
+@item --ignore-umask
+@FIXME{does this exist?}
-@node Adding Files, Appending Archives, Modifying, Modifying
-@subsection Adding Files to an Archive
-@cindex Adding files to an archive
-@cindex Updating an archive
+(See @samp{--preserve-permissions}; @pxref{Writing}.)
-To add files to an archive, use @samp{tar +add-file}. The archive to
-be added to must already exist and be in proper archive format (which
-normally means it was created previously using @code{tar}). If the
-archive was created with a different block size than now specified,
-@code{tar} will report an error (@pxref{Blocking Factor}). If the
-archive is not a valid @code{tar} archive, the results will be
-unpredictable. You cannot add files to a compressed archive, however
-you can add files to the last volume of a multi-volume archive.
-@xref{Matching Format Parameters}.
+@item --ignore-zeros
+@itemx -i
-The following example adds the file @file{shemp} to the archive
-@file{stooges} created above:
+With this option, @code{tar} will ignore zeroed blocks in the archive, which
+normally signals EOF. @xref{Reading}.
-@example
-tar +add-file +file=stooges shemp
-@end example
+@item --incremental
+@itemx -G
-You must specify the files to be added; there is no default.
+Used to inform @code{tar} that it is working with an old GNU-format
+incremental backup archive. It is intended primarily for backwards
+compatibility only. @FIXME-xref{}.
-@samp{tar +update} acts like @samp{tar +add-file}, but does not add
-files to the archive if there is already a file entry with that name
-in the archive that has the same modification time.
+@item --info-script=@var{script-file}
+@itemx --new-volume-script=@var{script-file}
+@itemx -F @var{script-file}
-Both @samp{+update} and @samp{+add-file} work by adding to the end of
-the archive. When you extract a file from the archive, only the
-version stored last will wind up in the file system. Because
-@samp{tar +extract} extracts files from an archive in sequence, and
-overwrites files with the same name in the file system, if a file name
-appears more than once in an archive the last version of the file will
-overwrite the previous versions which have just been extracted. You
-should avoid storing older versions of a file later in the archive.
+When @code{tar} is performing multi-tape backups, @var{script-file} is run
+at the end of each tape. @FIXME-xref{}.
-Note: @samp{+update} is not suitable for performing backups, because
-it doesn't change directory content entries, and because it lengthens
-the archive every time it is used.
-@c <<< xref to scripted backup, listed incremental, for info on backups.
+@item --interactive
+@itemx --confirmation
+@itemx -w
-@node Appending Archives, Deleting Archive Files, Adding Files, Modifying
-@subsection Appending One Archive's Contents to Another Archive
-@cindex Adding archives to an archive
-@cindex Concatenating Archives
+Specifies that @code{tar} should ask the user for confirmation before
+performing potentially destructive options, such as overwriting files.
+@FIXME-xref{}.
-To append copies of an archive or archives to the end of another
-archive, use @samp{tar +add-archive}. The source and target archives
-must already exist and have been created using compatable format
-parameters (@pxref{Matching Format Parameters}).
-
-@code{tar} will stop reading an archive if it encounters an
-end-of-archive marker. The @code{cat} utility does not remove
-end-of-archive markers, and is therefore unsuitable for concatenating
-archives. @samp{tar +add-archive} removes the end-of-archive marker
-from the target archive before each new archive is appended.
-@c <<< xref ignore-zeros
-
-You must specify the source archives using
-@samp{+file=@var{archive-name}} (@pxref{Archive Name}). If you do not
-specify the target archive , @code{tar} uses the value of the
-environment variable @code{TAPE}, or, if this has not been set, the
-default archive name.
+@item --keep-old-files
+@itemx -k
-The following example adds the contents of the archive
-@file{hail/hail/fredonia} to the archive @file{stooges} (both archives
-were created in examples above):
+When extracting files from an archive, @code{tar} will not overwrite existing
+files if this option is present. @xref{Writing}.
-@example
-tar +add-archive +file=stooges hail/hail/fredonia
-@end example
+@item --label=@var{name}
+@itemx -V @var{name}
-If you need to retrieve files from an archive that was added to using
-the @code{cat} utility, use the @samp{+ignore-zeros} option
-(@pxref{Archive Reading Options}).
+When creating an archive, instructs @code{tar} to write @var{name} as a name
+record in the archive. When extracting or listing archives, @code{tar} will
+only operate on archives that have a label matching the pattern
+specified in @var{name}. @FIXME-xref{}.
-@node Deleting Archive Files, Matching Format Parameters, Appending Archives, Modifying
-@subsection Deleting Files From an Archive
-@cindex Deleting files from an archive
-@cindex Removing files from an archive
+@item --listed-incremental=@var{snapshot-file}
+@itemx -g @var{snapshot-file}
-To delete archive members from an archive, use @samp{tar +delete}.
-You must specify the file names of the members to be deleted. All
-archive members with the specified file names will be removed from the
-archive.
+During a @samp{--create} operation, specifies that the archive that
+@code{tar} creates is a new GNU-format incremental backup, using
+@var{snapshot-file} to determine which files to backup.
+With other operations, informs @code{tar} that the archive is in incremental
+format. @FIXME-xref{}.
-The following example removes the file @file{curley} from the archive
-@file{stooges}:
+@item --mode=@var{permissions}
-@example
-tar +delete +file=stooges curley
-@end example
+When adding files to an archive, @code{tar} will use @var{permissions}
+for the archive members, rather than the permissions from the files.
+The program @code{chmod} and this @code{tar} option share the same syntax
+for what @var{permissions} might be. @xref{File permissions, Permissions,
+File permissions, filetutils, GNU file utilities}. This reference also
+has useful information for those not being overly familiar with the Unix
+permission system.
-You can only use @samp{tar +delete} on an archive if the archive
-device allows you to write to any point on the media.
+Of course, @var{permissions} might be plainly specified as an octal number.
+However, by using generic symbolic modifications to mode bits, this allows
+more flexibility. For example, the value @samp{a+rw} adds read and write
+permissions for everybody, while retaining executable bits on directories
+or on any other file already marked as executable.
-@quotation
-@strong{Warning:} Don't try to delete an archive member from a
-magnetic tape, lest you scramble the archive. There is no safe way
-(except by completely re-writing the archive) to delete files from
-most kinds of magnetic tape.
-@end quotation
+@item --multi-volume
+@itemx -M
-@c <<< MIB -- how about automatic detection of archive media? give error
-@c <<< unless the archive device is either an ordinary file or different
-@c <<< input and output (+file=-).
+Informs @code{tar} that it should create or otherwise operate on a
+multi-volume @code{tar} archive. @FIXME-xref{}.
-@node Matching Format Parameters, , Deleting Archive Files, Modifying
-@subsection Matching the Format Parameters
+@item --new-volume-script
-Some format parameters must be taken into consideration when modifying
-an archive:
+(see --info-script)
-Compressed archives cannot be modified.
+@item --newer=@var{date}
+@itemx --after-date=@var{date}
+@itemx -N
-You have to specify the block size of the archive when modifying an
-archive with a non-default block size.
+When creating an archive, @code{tar} will only add files that have changed
+since @var{date}. @FIXME-xref{}.
-Multi-volume archives can be modified like any other archive. To add
-files to a multi-volume archive, you need to only mount the last
-volume of the archive media (and new volumes, if needed). For all
-other operations, you need to use the entire archive.
-
-If a multi-volume archive was labeled using @samp{+label}
-(@pxref{Archive Label}) when it was created, @code{tar} will not
-automatically label volumes which are added later. To label
-subsequent volumes, specify @samp{+label=@var{archive-label}} again in
-conjunction with the @samp{+add-file}, @samp{+update} or
-@samp{+add-archive} operation.
-@cindex Labelling multi-volume archives
-@c <<< example
+@item --newer-mtime
-@c <<< xref somewhere, for more information about format parameters.
+In conjunction with @samp{--newer}, @code{tar} will only add files whose
+contents have changed (as opposed to just @samp{--newer}, which will
+also back up files for which any status information has changed).
-@node Listing Contents, Extracting From Archives, Modifying, Reading and Writing
-@section Listing the Contents of an Archive
-@cindex Names of the files in an archive
-@cindex Archive contents, list of
-@cindex Archive members, list of
+@item --no-recursion
-@samp{tar +list} prints a list of the file names of the archive
-members on the standard output. If you specify @var{file-name}
-arguments on the command line (or using the @samp{+files-from} option,
-@pxref{File Name Lists}), only the files you specify will be listed,
-and only if they exist in the archive. Files not specified will be
-ignored, unless they are under a specific directory.
+With this option, @code{tar} will not recurse into directories unless a
+directory is explicitly named as an argument to @code{tar}. @FIXME-xref{}.
-If you include the @samp{+verbose} option, @code{tar} prints an
-@samp{ls -l} type listing for the archive. @pxref{Additional
-Information}, for a description of the @samp{+verbose} option.
+@item --null
-If the blocking factor of the archive differs from the default,
-@code{tar} reports this. @xref{Blocking Factor}.
+When @code{tar} is using the @samp{--files-from} option, this option
+instructs @code{tar} to expect filenames terminated with @kbd{NUL}, so
+@code{tar} can correctly work with file names that contain newlines.
+@FIXME-xref{}.
-@xref{Archive Reading Options} for a list of options which can be used
-to modify @samp{+list}'s operation.
+@item --numeric-owner
-This example prints a list of the archive members of the archive
-@file{stooges}:
+This option will notify @code{tar} that it should use numeric user and group
+IDs when creating a @code{tar} file, rather than names. @FIXME-xref{}.
-@example
-tar +list +file=stooges
-@end example
+@item --old-archive
-@noindent
-@code{tar} responds:
+(See @samp{--portability}; @FIXME-pxref{}.)
-@example
-larry
-moe
-shemp
-marx/julius
-marx/alexander
-marx/karl
-@end example
+@item --one-file-system
+@itemx -l
-This example generates a verbose list of the archive members of the
-archive file @file{dwarves}, which has a blocking factor of two:
+Used when creating an archive. Prevents @code{tar} from recursing into
+directories that are on different file systems from the current
+directory. @FIXME-xref{}.
-@example
-tar +list -v +file=blocks
-@end example
+@item --owner=@var{user}
-@noindent
-@code{tar} responds:
+Specifies that @code{tar} should use @var{user} as the owner of members
+when creating archives, instead of the user associated with the source
+file. @var{user} is first decoded as a user symbolic name, but if
+this interpretation fails, it has to be a decimal numeric user ID.
+@FIXME-xref{}.
-@example
-tar: Blocksize = 2 records
--rw------- ringo/user 42 May 1 13:29 1990 .bashful
--rw-rw-rw- ringo/user 42 Oct 4 13:29 1990 doc
--rw-rw-rw- ringo/user 42 Jul 20 18:01 1969 dopey
--rw-rw---- ringo/user 42 Nov 26 13:42 1963 grumpy
--rw-rw-rw- ringo/user 42 May 5 13:29 1990 happy
--rw-rw-rw- ringo/user 42 May 1 12:00 1868 sleepy
--rw-rw-rw- ringo/user 42 Jul 4 17:29 1776 sneezy
-@end example
+There is no value indicating a missing number, and @samp{0} usually means
+@code{root}. Some people like to force @samp{0} as the value to offer in
+their distributions for the owner of files, because the @code{root} user is
+anonymous anyway, so that might as well be the owner of anonymous archives.
-@node Extracting From Archives, , Listing Contents, Reading and Writing
-@section Extracting Files from an Archive
-@cindex Extraction
-@cindex Retrieving files from an archive
-@cindex Resurrecting files from an archive
+@item --portability
+@itemx --old-archive
+@itemx -o
-To read archive members from the archive and write them into the file
-system, use @samp{tar +extract}. The archive itself is left
-unchanged.
+Tells @code{tar} to create an archive that is compatible with Unix V7
+@code{tar}. @FIXME-xref{}.
-If you do not specify the files to extract, @code{tar} extracts all
-the files in the archive. If you specify the name of a directory as a
-file-name argument, @code{tar} will extract all files which have been
-stored as part of that directory. If a file was stored with a
-directory name as part of its file name, and that directory does not
-exist under the working directory when the file is extracted,
-@code{tar} will create the directory. @xref{Selecting Archive
-Members}, for information on specifying files to extract.
+@item --posix
-The following example shows the extraction of the archive
-@file{stooges} into an empty directory:
+Instructs @code{tar} to create a POSIX compliant @code{tar} archive. @FIXME-xref{}.
-@example
-tar +extract +file=stooges
-@end example
+@item --preserve
-@noindent
-Generating a listing of the directory (@samp{ls}) produces:
+Synonymous with specifying both @samp{--preserve-permissions} and
+@samp{--same-order}. @FIXME-xref{}.
-@example
-larry
-moe
-shemp
-marx
-@end example
+@item --preserve-order
-@noindent
-The subdirectory @file{marx} contains the files @file{julius},
-@file{alexander} and @file{karl}.
+(See @samp{--same-order}; @pxref{Reading}.)
-If you wanted to just extract the files in the subdirectory
-@file{marx}, you could specify that directory as a file-name argument
-in conjunction with the @samp{+extract} operation:
+@item --preserve-permissions
+@itemx --same-permissions
+@itemx -p
-@example
-tar +extract +file=stooges marx
-@end example
+When @code{tar} is extracting an archive, it normally subtracts the users'
+umask from the permissions specified in the archive and uses that
+number as the permissions to create the destination file. Specifying
+this option instructs @code{tar} that it should use the permissions directly
+from the archive. @xref{Writing}.
-@quotation
-@strong{Warning:} Extraction can overwrite files in the file system.
-To avoid losing files in the file system when extracting files from
-the archive with the same name, use the @samp{+keep-old-files} option
-(@pxref{File Writing Options}).
-@end quotation
+@item --read-full-records
+@itemx -B
-If the archive was created using @samp{+block-size}, @samp{+compress}
-or @samp{+multi-volume}, you must specify those format options again
-when extracting files from the archive (@pxref{Format Variations}).
+Specifies that @code{tar} should reblock its input, for reading from pipes on
+systems with buggy implementations. @xref{Reading}.
-@menu
-* Archive Reading Options::
-* File Writing Options::
-* Scarce Disk Space:: Recovering From Scarce Disk Space
-@end menu
+@item --record-size=@var{size}
-@node Archive Reading Options, File Writing Options, Extracting From Archives, Extracting From Archives
-@subsection Options to Help Read Archives
-@cindex Options when reading archives
-@cindex Reading incomplete blocks
-@cindex Blocks, incomplete
-@cindex End of archive markers, ignoring
-@cindex Ignoring end of archive markers
-@cindex Large lists of file names on small machines
-@cindex Small memory
-@cindex Running out of space
+Instructs @code{tar} to use @var{size} bytes per record when accessing the
+archive. @FIXME-xref{}.
-@c <<< each option wants its own node. summary after menu
+@item --recursive-unlink
-Normally, @code{tar} will request data in full block increments from
-an archive storage device. If the device cannot return a full block,
-@code{tar} will report an error. However, some devices do not always
-return full blocks, or do not require the last block of an archive to
-be padded out to the next block boundary. To keep reading until you
-obtain a full block, or to accept an incomplete block if it contains
-an end-of-archive marker, specify the @samp{+read-full-blocks} option
-in conjunction with the @samp{+extract} or @samp{+list} operations.
-@xref{Listing Contents}.
-
-The @samp{+read-full-blocks} option is turned on by default when
-@code{tar} reads an archive from standard input, or from a remote
-machine. This is because on BSD Unix systems, attempting to read a
-pipe returns however much happens to be in the pipe, even if it is
-less than was requested. If this option were not enabled, @code{tar}
-would fail as soon as it read an incomplete block from the pipe.
+Similar to the @samp{--unlink-first} option, removing existing
+directory hierarchies before extracting directories of the same name
+from the archive. @xref{Writing}.
-If you're not sure of the blocking factor of an archive, you can read
-the archive by specifying @samp{+read-full-blocks} and
-@samp{+block-size=@var{n}}, where @var{n} is a blocking factor larger
-than the blocking factor of the archive. This lets you avoid having
-to determine the blocking factor of an archive. @xref{Blocking
-Factor}.
+@item --remove-files
-@table @samp
-@item +read-full-blocks
-@item -B
-Use in conjunction with @samp{tar +extract} to read an archive which
-contains incomplete blocks, or one which has a blocking factor less
-than the one specified.
-@end table
+Directs @code{tar} to remove the source file from the file system after
+appending it to an archive. @FIXME-xref{}.
-Normally @code{tar} stops reading when it encounters a block of zeros
-between file entries (which usually indicates the end of the archive).
-@samp{+ignore-zeros} allows @code{tar} to completely read an archive
-which contains a block of zeros before the end (i.e.@: a damaged
-archive, or one which was created by @code{cat}-ing several archives
-together).
+@item --rsh-command=@var{cmd}
-The @samp{+ignore-zeros} option is turned off by default because many
-versions of @code{tar} write garbage after the end of archive entry,
-since that part of the media is never supposed to be read. GNU
-@code{tar} does not write after the end of an archive, but seeks to
-maintain compatablity among archiving utilities.
+Notifies @code{tar} that is should use @var{cmd} to communicate with remote
+devices. @FIXME-xref{}.
-@table @samp
-@item +ignore-zeros
-@itemx -i
-To ignore blocks of zeros (ie.@: end-of-archive entries) which may be
-encountered while reading an archive. Use in conjunction with
-@samp{tar +extract} or @samp{tar +list}.
-@end table
+@item --same-order
+@itemx --preserve-order
+@itemx -s
-If you are using a machine with a small amount of memory, and you need
-to process large list of file-names, you can reduce the amount of
-space @code{tar} needs to process the list. To do so, specify the
-@samp{+same-order} option and provide an ordered list of file names.
-This option tells @code{tar} that the @file{file-name} arguments
-(provided on the command line, or read from a file using the
-@samp{+files-from} option) are listed in the same order as the files
-in the archive.
+This option is an optimization for @code{tar} when running on machines with
+small amounts of memory. It informs @code{tar} that the list of file
+arguments has already been sorted to match the order of files in the
+archive. @xref{Reading}.
-You can create a file containing an ordered list of files in the
-archive by storing the output produced by @samp{tar +list
-+file=@var{archive-name}}. @xref{Listing Contents}, for information
-on the @samp{+list} operation.
+@item --same-owner
-This option is probably never needed on modern computer systems.
+When extracting an archive, @code{tar} will attempt to preserve the owner
+specified in the @code{tar} archive with this option present. @FIXME-xref{}.
-@table @samp
-@item +same-order
-@itemx +preserve-order
-@itemx -s
-To process large lists of file-names on machines with small amounts of
-memory. Use in conjunction with @samp{tar +compare}, @samp{tar +list}
-or @samp{tar +extract}.
-@end table
+@item --same-permissions
-@c we don't need/want +preserve to exist any more
+(See @samp{--preserve-permissions}; @pxref{Writing}.)
-@node File Writing Options, Scarce Disk Space, Archive Reading Options, Extracting From Archives
-@subsection Changing How @code{tar} Writes Files
-@c <<< find a better title
-@cindex Overwriting old files, prevention
-@cindex Protecting old files
-@cindex Modification times of extracted files
-@cindex Permissions of extracted files
-@cindex Modes of extracted files
-@cindex Writing extracted files to standard output
-@cindex Standard output, writing extracted files to
+@item --show-omitted-dirs
-Normally, @code{tar} writes extracted files into the file system
-without regard to the files already on the system---files with the
-same name as archive members are overwritten. To prevent @code{tar}
-from extracting an archive member from an archive, if doing so will
-overwrite a file in the file system, use @samp{+keep-old-files} in
-conjunction with the @samp{+extract} operation. When this option is
-specified, @code{tar} reports an error stating the name of the files
-in conflict, instead of writing the file from the archive.
+Instructs @code{tar} to mention directories its skipping over when operating
+on a @code{tar} archive. @FIXME-xref{}.
-@table @samp
-@item +keep-old files
-@itemx -k
-Prevents @code{tar} from overwriting files in the file system during
-extraction.
-@end table
+@item --sparse
+@itemx -S
-Normally, @code{tar} sets the modification times of extracted files to
-the modification times recorded for the files in the archive, but
-limits the permissions of extracted files by the current @code{umask}
-setting.
+Invokes a GNU extension when adding files to an archive that handles
+sparse files efficiently. @FIXME-xref{}.
-To set the modification times of extracted files to the time when
-the files were extracted, use the @samp{+modification-time} option in
-conjunction with @samp{tar +extract}.
+@item --starting-file=@var{name}
+@itemx -K @var{name}
-@table @samp
-@item +modification-time
-@itemx -m
-Sets the modification time of extracted archive members to the time
-they were extracted, not the time recorded for them in the archive.
-Use in conjunction with @samp{+extract}.
-@end table
+This option affects extraction only; @code{tar} will skip extracting
+files in the archive until it finds one that matches @var{name}.
+@xref{Scarce}.
-To set the modes (access permissions) of extracted files to those
-recorded for those files in the archive, use the
-@samp{+preserve-permissions} option in conjunction with the
-@samp{+extract} operation.
-@c <<<mib --- should be aliased to ignore-umask.
+@item --suffix=@var{suffix}
-@table @samp
-@item +preserve-permission
-@itemx +same-permission
-@itemx +ignore-umask
-@itemx -p
-Set modes of extracted archive members to those recorded in the
-archive, instead of current umask settings. Use in conjunction with
-@samp{+extract}.
-@end table
+Alters the suffix @code{tar} uses when backing up files from the default
+@samp{~}. @FIXME-xref{}.
-@c <<< following paragraph needs to be rewritten:
-@c <<< why doesnt' this cat files together, why is this useful. is it
-@c <<< really useful with more than one file?
-To write the files extracted to the standard output, instead of
-creating the files on the file system, use @samp{+to-stdout} in
-conjunction with @samp{tar +extract}. This option is useful if you
-are extracting files to send them through a pipe, and do not need to
-preserve them in the file system.
+@item --tape-length=@var{num}
+@itemx -L @var{num}
-@table @samp
-@item +to-stdout
+Specifies the length of tapes that @code{tar} is writing as being
+@w{@var{num} x 1024} bytes long. @FIXME-xref{}.
+
+@item --to-stdout
@itemx -O
-Writes files to the standard output. Used in conjunction with
-@samp{+extract}.
-@end table
-@c <<< why would you want to do such a thing, how are files separated on
-@c <<< the standard output? is this useful with more that one file? are
-@c <<< pipes the real reason?
+During extraction, @code{tar} will extract files to stdout rather than to the
+file system. @xref{Writing}.
-@node Scarce Disk Space, , File Writing Options, Extracting From Archives
-@subsection Recovering From Scarce Disk Space
-@cindex Middle of the archive, starting in the
-@cindex Running out of space during extraction
-@cindex Disk space, running out of
-@cindex Space on the disk, recovering from lack of
+@item --totals
-If a previous attempt to extract files failed due to lack of disk
-space, you can use @samp{+starting-file=@var{file-name}} to start
-extracting only after file @var{file-name} when extracting files from
-the archive. This assumes, of course, that there is now free space,
-or that you are now extracting into a different file system.
+Displays the total number of bytes written after creating an archive.
+@FIXME-xref{}.
-@table @samp
-@item +starting-file=@var{file-name}
-@itemx -K @var{file-name}
-Starts an operation in the middle of an archive. Use in conjunction
-with @samp{+extract} or @samp{+list}.
-@end table
+@item --touch
+@itemx -m
-If you notice you are running out of disk space during an extraction
-operation, you can also suspend @code{tar}, remove unnecessary files
-from the file system, and then restart the same @code{tar} operation.
-In this case, @samp{+starting-file} is not necessary.
+Sets the modification time of extracted files to the extraction time,
+rather than the modification time stored in the archive.
+@xref{Writing}.
-@c <<< xref incremental, xref +interactive, xref +exclude
+@item --uncompress
-@node Insuring Accuracy, Selecting Archive Members, Reading and Writing, Top
-@chapter Insuring the Accuracy of an Archive
+(See @samp{--compress}; @FIXME-pxref{}.)
-You can insure the accuracy of an archive by comparing files in the
-system with archive members. @code{tar} can compare an archive to the
-file system as the archive is being written, to verify a write
-operation, or can compare a previously written archive, to insure that
-it is up to date.
+@item --ungzip
-@menu
-* Write Verification::
-* Comparing::
-@end menu
+(See @samp{--gzip}; @FIXME-pxref{}.)
-@node Write Verification, Comparing, Insuring Accuracy, Insuring Accuracy
-@section Verifying Data as It is Stored
-@cindex Verifying a write operation
-@cindex Double-checking a write operation
+@item --unlink-first
+@itemx -U
-To check for discrepancies in an archive immediately after it is
-written, use the @samp{+verify} option in conjunction with the
-@samp{tar +create} operation. When this option is specified,
-@code{tar} checks archive members against their counterparts in the file
-system, and reports discrepancies on the standard error. In
-multi-volume archives, each volume is verified after it is written,
-before the next volume is written.
+Directs @code{tar} to remove the corresponding file from the file system
+before extracting it from the archive. @xref{Writing}.
-To verify an archive, you must be able to read it from before the end
-of the last written entry. This option is useful for detecting data
-errors on some tapes. Archives written to pipes, some cartridge tape
-drives, and some other devices cannot be verified.
+@item --use-compress-program=@var{prog}
-@table @samp
-@item +verify
+Instructs @code{tar} to access the archive through @var{prog}, which is
+presumed to be a compression program of some sort. @FIXME-xref{}.
+
+@item --verbose
+@itemx -v
+
+Specifies that @code{tar} should be more verbose about the operations its
+performing. This option can be specified multiple times for some
+operations to increase the amount of information displayed. @FIXME-xref{}.
+
+@item --verify
@itemx -W
-Checks for discrepancies in the archive immediately after it is
-written. Use in conjunction with @samp{tar +create}.
+
+Verifies that the archive was correctly written when creating an
+archive. @FIXME-xref{}.
+
+@item --version
+
+@code{tar} will print an informational message about what version it is and a
+copyright message, some credits, and then exit. @FIXME-xref{}.
+
+@item --volno-file=@var{file}
+
+Used in conjunction with @samp{--multi-volume}. @code{tar} will keep track
+of which volume of a multi-volume archive its working in @var{file}.
+@FIXME-xref{}.
@end table
-@node Comparing, , Write Verification, Insuring Accuracy
-@section Comparing an Archive with the File System
-@cindex Verifying the currency of an archive
+@node Short Option Summary, , Option Summary, All Options
+@subsection Short Options Cross Reference
-@samp{tar +compare} compares archive members in an existing archive
-with their counterparts in the file system, and reports differences in
-file size, mode, owner, modification date and contents. If a file is
-represented in the archive but does not exist in the file system,
-@code{tar} reports a difference.
-
-If you use @var{file-name} arguments in conjunction with @samp{tar
-+compare}, @code{tar} compares the archived versions of the files
-specified with their counterparts in the file system. If you specify
-a file that is not in the archive, @code{tar} will report an error. If
-you don't specify any files, @code{tar} compares all the files in the
-archive.
+Here is an alphabetized list of all of the short option forms, matching
+them with the equivalent long option.
-Because @code{tar} only checks files in the archive against files in
-the file system, and not vice versa, it ignores files in the file
-system that do not exist in the archive.
+@table @kbd
-The following example compares the archive members @file{larry},
-@file{moe} and @file{curly} in the archive @file{stooges} with files
-of the same name in the file system.
+@item -A
-@example
-tar +compare +file=stooges larry moe curly
-@end example
+@samp{--concatenate}
-@noindent
-If a file, for example @file{curly}, did not exist in the archive,
-@code{tar} would report an error, as follows:
+@item -B
-@example
-curly: does not exist
-@end example
+@samp{--read-full-records}
-@node Selecting Archive Members, User Interaction, Insuring Accuracy, Top
-@chapter Selecting Archive Members
-@cindex Specifying files to act on
-@cindex Specifying archive members
+@item -C
-@dfn{File-name arguments} specify which files in the file system
-@code{tar} operates on, when creating or adding to an archive, or
-which archive members @code{tar} operates on, when reading or
-deleting from an archive. (@pxref{Reading and Writing}.)
+@samp{--directory}
-To specify file names, you can include them as the last arguments on
-the command line, as follows:
-@example
-tar @var{operation} [@var{option1} @var{option2} ..] [@var{file-name-1} @var{file-name-2} ...]
-@end example
+@item -F
-If you specify a directory name as a file name argument, all the files
-in that directory are operated on by @code{tar}.
+@samp{--info-script}
-If you do not specify files when @code{tar} is invoked, @code{tar}
-operates on all the non-directory files in the working directory (if
-the operation is @samp{+create}), all the archive members in the
-archive (if a read operation is specified), or does nothing (if any
-other operation is specified).
+@item -G
-@menu
-* File Name Lists:: Reading File Names from a File
-* File Name Interpretation:: this needs a better title
-* File Exclusion:: so does this
-@end menu
+@samp{--incremental}
-@node File Name Lists, File Name Interpretation, Selecting Archive Members, Selecting Archive Members
-@section Reading a List of File Names from a File
-@cindex Lists of file names
-@cindex File-name arguments, alternatives
+@item -K
-To read file names from a file on the file system, instead of from the
-command line, use the @samp{+files-from=@var{file}} option. If you
-specify @samp{-} as @var{file}, the file names are read from standard
-input. Note that using both @samp{+files-from=-} and @samp{+file=-}
-in the same command will not work unless the operation is
-@samp{+create}. @xref{Archive Name}, for an explanation of the
-@samp{+file} option.
+@samp{--starting-file}
-@table @samp
-@item +files-from=@var{file}
-@itemx -T @var{file}
-Reads file-name arguments from a file on the file system, instead of
-from the command line. Use in conjunction with any operation.
-@end table
+@item -L
-@node File Name Interpretation, File Exclusion, File Name Lists, Selecting Archive Members
-@section File Name Interpretation
-@cindex File Names, interpreting
+@samp{--tape-length}
-@c <<<<add some text -ringo
+@item -M
-@menu
-* Absolute File Names::
-* Changing Working Directory::
-* Archiving with Symbolic Links:: Archiving Using Symbolic Links
-@end menu
+@samp{--multi-volume}
-@node Absolute File Names, Changing Working Directory, File Name Interpretation, File Name Interpretation
-@subsection Storing and Extracting Files Relative to Root
+@item -N
-@c <<< is this what this does, or does it just preserve the slash?
-@c <<< is it still called +absolute-paths?
+@samp{--newer}
-@c To archive or extract files relative to the root directory, specify
-@c the @samp{+absolute-paths} option.
+@item -O
-@c Normally, @code{tar} acts on files relative to the working
-@c directory---ignoring superior directory names when archiving, and
-@c ignoring leading slashes when extracting.
+@samp{--to-stdout}
-@c When you specify @samp{+absolute-paths}, @code{tar} stores file names
-@c including all superior directory names, and preserves leading slashes.
-@c If you only invoked @code{tar} from the root directory you would never
-@c need the @samp{+absolute-paths} option, but using this option may be
-@c more convenient than switching to root.
+@item -P
-@c >>> should be an example in the tutorial/wizardry section using this
-@c >>> to transfer files between systems.
+@samp{--absolute-names}
-@c >>> is write access an issue?
+@item -R
-@table @samp
-@item +absolute-paths
-Preserves full file names (inclusing superior dirctory names) when
-archiving files. Preserves leading slash when extracting files.
-@end table
+@samp{--block-number}
-@node Changing Working Directory, Archiving with Symbolic Links, Absolute File Names, File Name Interpretation
-@subsection Changing the Working Directory Within a List of File-names
-@cindex Directory, changing in mid-stream
-@cindex Working directory, specifying
+@item -S
-To change working directory in the middle of a list of file names,
-(either on the command line or in a file specified using
-@samp{+files-from}), use @samp{+directory=@var{directory}}. This will
-change the working directory to the directory @var{directory} after
-that point in the list. For example,
+@samp{--sparse}
-@example
-tar +create iggy ziggy +directory=baz melvin
-@end example
+@item -T
-@noindent
-will place the files @file{iggy} and @file{ziggy} from the current
-directory into the archive, followed by the file @file{melvin} from
-the directory @file{baz}. This option is especially useful when you
-have several widely separated files that you want to store in the same
-directory in the archive.
-
-Note that the file @file{melvin} is recorded in the archive under the
-precise name @file{melvin}, @emph{not} @file{baz/melvin}. Thus, the
-archive will contain three files that all appear to have come from the
-same directory; if the archive is extracted with plain @samp{tar
-+extract}, all three files will be written in the current directory.
+@samp{--files-from}
-Contrast this with the command
+@item -U
-@example
-tar -c iggy ziggy bar/melvin
-@end example
+@samp{--unlink-first}
-@noindent
-which records the third file in the archive under the name
-@file{bar/melvin} so that, if the archive is extracted using @samp{tar
-+extract}, the third file will be written in a subdirectory named
-@file{bar}.
+@item -V
-@table @samp
-@item +directory=@file{directory}
-@itemx -C @file{directory}
-Changes the working directory.
-@end table
+@samp{--label}
-@c <<<need to test how extract deals with this, and add an example -ringo
+@item -W
-@node Archiving with Symbolic Links, , Changing Working Directory, File Name Interpretation
-@subsection Archiving Using Symbolic Links
-@cindex File names, using symbolic links
-@cindex Symbolic link as file name
+@samp{--verify}
-@samp{+dereference} is used with @samp{tar +create}, and causes
-@code{tar} to archive files which are referenced by a symbolic link,
-using the name of the link as the file name.
+@item -X
-<<<this needs to be checked by MIB and then re-written, with an example
-The name under which the file is stored in the file system is not
-recorded in the archive. To record both the symbolic link name and
-the file name in the system, archive the file under both names. If
-all links were recorded automatically by @code{tar}, an extracted file
-might be linked to a file name that no longer exists in the file
-system.
+@samp{--exclude-from}
-@c <<< is the following still true? - ringo
-If a linked-to file is encountered again by @code{tar} while creating
-the same archive, an entire second copy of it will be stored. This
-could be considered a bug.
+@item -Z
-@table @samp
-@item +dereference
-@itemx -h
-Stores files referenced by a symbolic link, using the name of the link
-as the file name. Use in conjunction with any write operation.
-@end table
+@samp{--compress}
-@node File Exclusion, , File Name Interpretation, Selecting Archive Members
-@section Selecting Files by Characteristic
-@cindex File names, excluding files by
-@cindex Excluding files by name and pattern
-@cindex Excluding files by file system
-@cindex File system boundaries, not crossing
-@cindex Excluding file by age
-@cindex Modification time, excluding files by
-@cindex Age, excluding files by
+@item -b
-To avoid crossing file system boundaries when archiving parts of a
-directory tree, use @samp{+one-file-system}. This option only affects
-files that are archived because they are in a directory that is being
-archived; files explicitly named on the command line are archived
-regardless of where they reside.
+@samp{--blocking-factor}
-This option is useful for making full or incremental archival backups
-of a file system.
+@item -c
-If this option is used in conjunction with @samp{+verbose}, files that
-are excluded are mentioned by name on the standard error.
+@samp{--create}
-@table @samp
-@item +one-file-system
-@itemx -l
-Prevents @code{tar} from crossing file system boundaries when
-archiving. Use in conjunction with any write operation.
-@end table
+@item -d
-To avoid operating on files whose names match a particular pattern,
-use the @samp{+exclude=@var{pattern}} or
-@samp{+exclude-from=@var{file}} options.
+@samp{--compare}
-When you specify the @samp{+exclude=@var{pattern}} option, @code{tar}
-ignores files which match the @var{pattern}, which can be a single
-file name or a more complex expression. Thus, if you invoke
-@code{tar} with @samp{tar +create +exclude=*.o}, no files whose names
-end in @file{.o} are included in the archive.
-@c <<< what other things can you use besides "*"?
+@item -f
-@samp{+exclude-from=@var{file}} acts like @samp{+exclude}, but
-specifies a file @var{file} containing a list of patterns. @code{tar}
-ignores files with names that fit any of these patterns.
+@samp{--file}
-You can use either option more than once in a single command.
+@item -g
-@table @samp
-@item +exclude=@var{pattern}
-Causes @code{tar} to ignore files that match the @var{pattern}.
+@samp{--listed-incremental}
-@item +exclude-from=@var{file}
-Causes @code{tar} to ignore files that match the patterns listed in
-@var{file}.
-@end table
-@c +exclude-from used to be "+exclude", +exclude didn't used to exist.
+@item -h
+
+@samp{--dereference}
-To operate only on files with modification or status-change times
-after a particular date, use @samp{+after-date=@var{date}}. You can
-use this option with @samp{tar +create} or @samp{tar +add-file} to
-insure only new files are archived, or with @samp{tar +extract} to
-insure only recent files are resurrected. @refill
-@c +after-date @var{date} or +newer @var{date}
+@item -i
-@samp{+newer-mtime=@var{date}} acts like @samp{+after-date=@var{date}},
-but tests just the modification times of the files, ignoring
-status-change times.
+@samp{--ignore-zeros}
-@c <<<need example of +newer-mtime with quoted argument
-Remember that the entire date argument should be quoted if it contains
-any spaces.
+@item -k
+@samp{--keep-old-files}
-@strong{Please Note:} @samp{+after-date} and @samp{+newer-mtime}
-should not be used for incremental backups. Some files (such as those
-in renamed directories) are not selected up properly by these options.
-@c xref to incremental backup chapter when node name is decided.
+@item -l
-@table @samp
-@item +after-date=@var{date}
-@itemx +newer=@var{date}
-@itemx -N @var{date}
-Acts on files only if their modification or inode-changed times are
-later than @var{date}. Use in conjunction with any operation.
-@item +newer-mtime=@var{date}
-Acts like @samp{+after-date}, but only looks at modification times.
-@end table
+@samp{--one-file-system}
-@c <<< following is the getdate date format --- needs to be re-written,
-@c <<< made a sub-node:
+@item -m
-Time/Date Formats Accepted by getdate
-(omitting obscure constructions)
+@samp{--touch}
-The input consists of one or more of: time zone day date year
-in any order.
+@item -o
-Those in turn consist of (`|' and `/' mean `or', `[]' means `optional'):
+@samp{--portability}
-time: H am/pm | H:M [am/pm] | H:M:S [am/pm]
-zone: timezone-name | timezone-name dst
-day: day-name | day-name, | N day-name
-date: M/D | M/D/Y | month-name D | month-name D, Y | D month-name | D month-name Y
-year: Y
+@item -p
-am can also be a.m., pm can also be p.m.
-case and spaces around punctuation are not significant.
-month and day names can be abbreviated. >>>
+@samp{--preserve-permissions}
-@node User Interaction, Backups and Restoration, Selecting Archive Members, Top
-@chapter User Interaction
-@cindex Getting more information during the operation
-@cindex Information during operation
-@cindex Feedback from @code{tar}
+@item -r
-Once you have typed a @code{tar}command, it is usually performed
-without any further information required of the user, or provided by
-@code{tar}. The following options allow you to generate progress and
-status information during an operation, or to confirm operations on
-files as they are performed.
+@samp{--append}
-@menu
-* Additional Information::
-* Interactive Operation::
-@end menu
+@item -s
-@node Additional Information, Interactive Operation, User Interaction, User Interaction
-@section Progress and Status Information
-@cindex Progress information
-@cindex Status information
-@cindex Information on progress and status of operations
-@cindex Verbose operation
-@cindex Record number where error occured
-@cindex Error message, record number of
-@cindex Version of the @code{tar} program
+@samp{--same-order}
-Typically, @code{tar} performs most operations without reporting any
-information to the user except error messages. If you have
-encountered a problem when operating on an archive, however, you may
-need more information than just an error message in order to solve the
-problem. The following options can be helpful diagnostic tools.
-
-When used with most operations, @samp{+verbose} causes @code{tar} to
-print the file names of the files or archive members it is operating
-on. When used with @samp{tar +list}, the verbose option causes
-@code{tar} to print out an @samp{ls -l} type listing of the files in
-the archive.
-
-Verbose output appears on the standard output except when an archive
-is being written to the standard output (as with @samp{tar +create
-+file=- +verbose}). In that case @code{tar} writes verbose output to
-the standard error stream.
+@item -t
-@table @samp
-@item +verbose
-@itemx -v
-Prints the names of files or archive members as they are being
-operated on. Can be used in conjunction with any operation. When
-used with @samp{+list}, generates an @samp{ls -l} type listing.
-@end table
+@samp{--list}
-To find out where in an archive a message was triggered, use
-@samp{+record-number}. @samp{+record-number} causes @code{tar} to
-print, along with every message it produces, the record number within
-the archive where the message was triggered.
+@item -u
-This option is especially useful when reading damaged archives, since
-it helps pinpoint the damaged sections. It can also be used with
-@samp{tar +list} when listing a file-system backup tape, allowing you
-to choose among several backup tapes when retrieving a file later, in
-favor of the tape where the file appears earliest (closest to the
-front of the tape).
-@c <<< xref when the node name is set and the backup section written
+@samp{--update}
-@table @samp
-@item +record-number
-@itemx -R
-Prints the record number whenever a message is generated by
-@code{tar}. Use in conjunction with any operation.
-@end table
+@item -v
-@c rewrite below
-To print the version number of the @code{tar} program, use @samp{tar
-+version}. @code{tar} prints the version number to the standard
-error. For example:
+@samp{--verbose}
-@example
-tar +version
-@end example
+@item -w
-@noindent
-might return:
+@samp{--interactive}
-@example
-GNU tar version 1.09
-@end example
-@c used to be an option. has been fixed.
+@item -x
-@node Interactive Operation, , Additional Information, User Interaction
-@section Asking for Confirmation During Operations
-@cindex Interactive operation
+@samp{--extract}
-Typically, @code{tar} carries out a command without stopping for
-further instructions. In some situations however, you
-may want to exclude some files and archive members from the operation
-(for instance if disk or storage space is tight). You can do this by
-excluding certain files automatically (@pxref{File Exclusion}), or by
-performing an operation interactively, using the @samp{+interactive}
-operation.
-
-When the @samp{+interactive} option is specified, @code{tar} asks for
-confirmation before reading, writing, or deleting each file it
-encounters while carrying out an operation. To confirm the action you
-must type a line of input beginning with @samp{y}. If your input line
-begins with anything other than @samp{y}, @code{tar} skips that file.
-
-Commands which might be useful to perform interactively include
-appending files to an archive, extracting files from an archive,
-deleting a file from an archive, and deleting a file from disk during
-an incremental restore.
+@item -z
-If @code{tar} is reading the archive from the standard input,
-@code{tar} opens the file @file{/dev/tty} to support the interactive
-communications.
-<<< this aborts if you won't OK the working directory. this is a bug. -ringo
+@samp{--gzip}
-@table @samp
-@item +interactive
-@itemx +confirmation
-@itemx -w
-Asks for confirmation before reading, writing or deleting an archive
-member (when listing, comparing or writing an archive or deleting
-archive members), or before writing or deleting a file (when
-extracting an archive).
@end table
-@node Backups and Restoration, Media, User Interaction, Top
-@chapter Performing Backups and Restoring Files
+@node help, verbose, All Options, tar invocation
+@section GNU @code{tar} documentation
-To @dfn{back up} a file system means to create archives that contain
-all the files in that file system. Those archives can then be used to
-restore any or all of those files (for instance if a disk crashes or a
-file is accidently deleted). File system @dfn{backups} are also
-called @dfn{dumps}.
+Being careful, the first thing is really checking that you are using GNU
+@code{tar}, indeed. The @value{op-version} option will generate a message
+giving confirmation that you are using GNU @code{tar}, with the precise
+version of GNU @code{tar} you are using. @code{tar} identifies itself
+and prints the version number to the standard output, then immediately
+exits successfully, without doing anything else, ignoring all other
+options. For example, @w{@samp{tar --version}} might return:
-@menu
-* Backup Levels:: Levels of backups
-* Backup Scripts:: Using scripts to perform backups
- and restoration
-* incremental and listed-incremental:: The +incremental
- and +listed-incremental Options
-* Problems:: Some common problems and their solutions
-@end menu
+@example
+tar (GNU tar) @value{VERSION}
+@end example
-@node Backup Levels, Backup Scripts, Backups and Restoration, Backups and Restoration
-@section Levels of Backups
+@noindent
+The first occurrence of @samp{tar} in the result above is the program
+name in the package (for example, @code{rmt} is another program), while
+the second occurrence of @samp{tar} is the name of the package itself,
+containing possibly many programs. The package is currently named
+@samp{tar}, after the name of the main program it contains@footnote{There
+are plans to merge the @code{cpio} and @code{tar} packages into a single one
+which would be called @code{paxutils}. So, who knows if, one of this days,
+the @value{op-version} would not yield @w{@samp{tar (GNU paxutils) 3.2}}}.
+
+Another thing you might want to do is checking the spelling or meaning
+of some particular @code{tar} option, without resorting to this manual,
+for once you have carefully read it. GNU @code{tar} has a short help
+feature, triggerable through the @value{op-help} option. By using this
+option, @code{tar} will print a usage message listing all available
+options on standard output, then exit successfully, without doing
+anything else and ignoring all other options. Even if this is only a
+brief summary, it may be several screens long. So, if you are not
+using some kind of scrollable window, you might prefer to use something
+like:
-An archive containing all the files in the file system is called a
-@dfn{full backup} or @dfn{full dump}. You could insure your data by
-creating a full dump every day. This strategy, however, would waste a
-substantial amount of archive media and user time, as unchanged files
-are daily re-archived.
+@example
+$ @kbd{tar --help | less}
+@end example
-It is more efficient to do a full dump only occasionally. To back up
-files between full dumps, you can a incremental dump. A @dfn{level
-one} dump archives all the files that have changed since the last full
-dump.
+@noindent
+presuming, here, that you like using @code{less} for a pager. Other
+popular pagers are @code{more} and @code{pg}. If you know about some
+@var{keyword} which interests you and do not want to read all the
+@value{op-help} output, another common idiom is doing:
-A typical dump strategy would be to perform a full dump once a week,
-and a level one dump once a day. This means some versions of files
-will in fact be archived more than once, but this dump strategy makes
-it possible to restore a file system to within one day of accuracy by
-only extracting two archives---the last weekly (full) dump and the
-last daily (level one) dump. The only information lost would be in
-files changed or created since the last daily backup. (Doing dumps
-more than once a day is usually not worth the trouble).
+@example
+tar --help | grep @var{keyword}
+@end example
-@node Backup Scripts, incremental and listed-incremental, Backup Levels, Backups and Restoration
-@section Using Scripts to Perform Backups and Restoration
+@noindent
+for getting only the pertinent lines.
+
+The perceptive reader would have noticed some contradiction in the
+previous paragraphs. It is written that both @value{op-version} and
+@value{op-help} print something, and have all other options ignored. In
+fact, they cannot ignore each other, and one of them has to win. We do
+not specify which is stronger, here; experiment if you really wonder!
+
+The short help output is quite succint, and you might have to get back
+to the full documentation for precise points. If you are reading this
+paragraph, you already have the @code{tar} manual in some form. This
+manual is available in printed form, as a kind of small book. It may
+printed out of the GNU @code{tar} distribution, provided you have @TeX{}
+already installed somewhere, and a laser printer around. Just configure
+the distribution, execute the command @w{@samp{make dvi}}, then print
+@file{doc/tar.dvi} the usual way (contact your local guru to know how).
+If GNU @code{tar} has been conveniently installed at your place, this
+manual is also available in interactive, hypertextual form as an Info
+file. Just call @w{@samp{info tar}} or, if you do not have the
+@code{info} program handy, use the Info reader provided within GNU
+Emacs, calling @samp{tar} from the main Info menu.
+
+There is currently no @code{man} page for GNU @code{tar}. If you observe
+such a @code{man} page on the system you are running, either it does not
+long to GNU @code{tar}, or it has not been produced by GNU. Currently,
+GNU @code{tar} documentation is provided in Texinfo format only, if we
+except, of course, the short result of @kbd{tar --help}.
+
+@node verbose, interactive, help, tar invocation
+@section Checking @code{tar} progress
-GNU @code{tar} comes with scripts you can use to do full and level-one
-dumps. Using scripts (shell programs) to perform backups and
-restoration is a convenient and reliable alternative to typing out
-file name lists and @code{tar} commands by hand.
+@cindex Progress information
+@cindex Status information
+@cindex Information on progress and status of operations
+@cindex Verbose operation
+@cindex Block number where error occured
+@cindex Error message, block number of
+@cindex Version of the @code{tar} program
-Before you use these scripts, you need to edit the file
-@file{backup-specs}, which specifies parameters used by the backup
-scripts and by the restore script. @xref{Script Syntax}.
-Once the backup parameters are set, you can perform backups or
-restoration by running the appropriate script.
-
-The name of the restore script is @code{restore}. The names of the
-level one and full backup scripts are, respectively, @code{level-1} and
-@code{level-0}. The @code{level-0} script also exists under the name
-@code{weekly}, and the @code{level-1} under the name
-@code{daily}---these additional names can be changed according to your
-backup schedule. @xref{Scripted Restoration}, for more information
-on running the restoration script. @xref{Scripted Backups}, for more
-information on running the backup scripts.
+@cindex Getting more information during the operation
+@cindex Information during operation
+@cindex Feedback from @code{tar}
-@emph{Please Note:} The backup scripts and the restoration scripts are
-designed to be used together. While it is possible to restore files
-by hand from an archive which was created using a backup script, and
-to create an archive by hand which could then be extracted using the
-restore script, it is easier to use the scripts. @xref{incremental
-and listed-incremental}, before making such an attempt.
+Typically, @code{tar} performs most operations without reporting any
+information to the user except error messages. When using @code{tar}
+with many options, particularly ones with complicated or
+difficult-to-predict behavior, it is possible to make serious mistakes.
+@code{tar} provides several options that make observing @code{tar}
+easier. These options cause @code{tar} to print information as it
+progresses in its job, and you might want to use them just for being
+more careful about what is going on, or merely for entertaining
+yourself. If you have encountered a problem when operating on an
+archive, however, you may need more information than just an error
+message in order to solve the problem. The following options can be
+helpful diagnostic tools.
+
+Normally, the @value{op-list} command to list an archive prints just
+the file names (one per line) and the other commands are silent.
+When used with most operations, the @value{op-verbose} option causes
+@code{tar} to print the name of each file or archive member as it
+is processed. This and the other options which make @code{tar} print
+status information can be useful in monitoring @code{tar}.
+
+With @value{op-create} or @value{op-extract}, @value{op-verbose} used once
+just prints the names of the files or members as they are processed.
+Using it twice causes @code{tar} to print a longer listing (reminiscent
+of @samp{ls -l}) for each member. Since @value{op-list} already prints
+the names of the members, @value{op-verbose} used once with @value{op-list}
+causes @code{tar} to print an @samp{ls -l} type listing of the files
+in the archive. The following examples both extract members with
+long list output:
+
+@example
+$ @kbd{tar --extract --file=archive.tar --verbose --verbose}
+$ @kbd{tar xvv archive.tar}
+@end example
+
+Verbose output appears on the standard output except when an archive is
+being written to the standard output, as with @samp{tar --create
+--file=- --verbose} (@samp{tar cfv -}, or even @samp{tar cv}---if the
+installer let standard output be the default archive). In that case
+@code{tar} writes verbose output to the standard error stream.
+
+The @value{op-totals} option---which is only meaningful when used with
+@value{op-create}---causes @code{tar} to print the total
+amount written to the archive, after it has been fully created.
+
+The @value{op-checkpoint} option prints an occasional message
+as @code{tar} reads or writes the archive. In fact, it print
+directory names while reading the archive. It is designed for
+those who don't need the more detailed (and voluminous) output of
+@value{op-block-number}, but do want visual confirmation that @code{tar}
+is actually making forward progress.
+
+@FIXME{There is some confusion here. It seems that -R once wrote a
+message at @samp{every} record read or written.}
+
+The @value{op-show-omitted-dirs} option, when reading an archive---with
+@value{op-list} or @value{op-extract}, for example---causes a message
+to be printed for each directory in the archive which is skipped.
+This happens regardless of the reason for skipping: the directory might
+not have been named on the command line (implicitly or explicitly),
+it might be excluded by the use of the @value{op-exclude} option, or
+some other reason.
+
+If @value{op-block-number} is used, @code{tar} prints, along with every
+message it would normally produce, the block number within the archive
+where the message was triggered. Also, supplementary messages are
+triggered when reading blocks full of NULs, or when hitting end of file on
+the archive. As of now, if the archive if properly terminated with a NUL
+block, the reading of the file may stop before end of file is met, so the
+position of end of file will not usually show when @value{op-block-number}
+is used. Note that GNU @code{tar} drains the archive before exiting when
+reading the archive from a pipe.
+
+This option is especially useful when reading damaged archives, since
+it helps pinpoint the damaged sections. It can also be used with
+@value{op-list} when listing a file-system backup tape, allowing you to
+choose among several backup tapes when retrieving a file later, in
+favor of the tape where the file appears earliest (closest to the
+front of the tape). @FIXME-xref{when the node name is set and the
+backup section written}.
+
+@node interactive, , verbose, tar invocation
+@section Asking for Confirmation During Operations
+@cindex Interactive operation
+
+Typically, @code{tar} carries out a command without stopping for
+further instructions. In some situations however, you may want to
+exclude some files and archive members from the operation (for instance
+if disk or storage space is tight). You can do this by excluding
+certain files automatically (@pxref{Choosing}), or by performing
+an operation interactively, using the @value{op-interactive} option.
+@code{tar} also accepts @samp{--confirmation} for this option.
+
+When the @value{op-interactive} option is specified, before
+reading, writing, or deleting files, @code{tar} first prints a message
+for each such file, telling what operation it intends to take, then asks
+for confirmation on the terminal. The actions which require
+confirmation include adding a file to the archive, extracting a file
+from the archive, deleting a file from the archive, and deleting a file
+from disk. To confirm the action, you must type a line of input
+beginning with @samp{y}. If your input line begins with anything other
+than @samp{y}, @code{tar} skips that file.
+
+If @code{tar} is reading the archive from the standard input,
+@code{tar} opens the file @file{/dev/tty} to support the interactive
+communications.
+
+Verbose output is normally sent to standard output, separate from
+other error messages. However, if the archive is produced directly
+on standard output, then verbose output is mixed with errors on
+@code{stderr}. Producing the archive on standard output may be used
+as a way to avoid using disk space, when the archive is soon to be
+consumed by another process reading it, say. Some people felt the need
+of producing an archive on stdout, still willing to segregate between
+verbose output and error output. A possible approach would be using a
+named pipe to receive the archive, and having the consumer process to
+read from that named pipe. This has the advantage of letting standard
+output free to receive verbose output, all separate from errors.
+
+@node operations, Backups, tar invocation, Top
+@chapter GNU @code{tar} Operations
-@c shorten node names
@menu
-* Backup Parameters:: Setting parameters for backups and restoration
-* Scripted Backups:: Using the backup scripts
-* Scripted Restoration:: Using the restore script
+* Basic tar::
+* Advanced tar::
+* extract options::
+* backup::
+* Applications::
+* looking ahead::
@end menu
-@node Backup Parameters, Scripted Backups, Backup Scripts, Backup Scripts
-@subsection Setting Parameters for Backups and Restoration
+@node Basic tar, Advanced tar, operations, operations
+@section Basic GNU @code{tar} Operations
-The file @file{backup-specs} specifies backup parameters for the
-backup and restoration scripts provided with @code{tar}. You must
-edit @file{backup-specs} to fit your system configuration and schedule
-before using these scripts.
+The basic @code{tar} operations, @value{op-create}, @value{op-list} and
+@value{op-extract}, are currently presented and described in the tutorial
+chapter of this manual. This section provides some complementary notes
+for these operations.
-@c <<< This about backup scripts needs to be written:
-@c <<<BS is a shell script .... thus ... @file{backup-specs} is in shell
-@c script syntax. @xref{Script Syntax}, for an explanation of this
-@c syntax.
+@table @asis
+@item @value{op-create}
-@c whats a parameter .... looked at by the backup scripts ... which will
-@c be expecting to find ... now syntax ... value is linked to lame ...
-@c @file{backup-specs} specifies the following parameters:
+Creating an empty archive would have some kind of elegance. One can
+initialize an empty archive and later use @value{op-append} for adding
+all members. Some applications would not welcome making an exception
+in the way of adding the first archive member. On the other hand,
+many people reported that it is dangerously too easy for @code{tar}
+to destroy a magnetic tape with an empty archive@footnote{This is well
+described in @cite{Unix-haters Handbook}, by Simson Garfinkel, Daniel
+Weise & Steven Strassmann, IDG Books, ISBN 1-56884-203-1.}. The two most
+common errors are:
+@enumerate
+@item
+Mistakingly using @code{create} instead of @code{extract}, when the
+intent was to extract the full contents of an archive. This error
+is likely: keys @kbd{c} and @kbd{x} are right next ot each other on
+the QWERTY keyboard. Instead of being unpacked, the archive then
+gets wholly destroyed. When users speak about @dfn{exploding} an
+archive, they usually mean something else :-).
-@table @code
-@item ADMINISTRATOR
-The user name of the backup administrator.
+@item
+Forgetting the argument to @code{file}, when the intent was to create
+an archive with a single file in it. This error is likely because a
+tired user can easily add the @kbd{f} key to the cluster of option
+letters, by the mere force of habit, without realizing the full
+consequence of doing so. The usual consequence is that the single
+file, which was meant to be saved, is rather destroyed.
+@end enumerate
+
+So, recognizing the likelihood and the catastrophical nature of these
+errors, GNU @code{tar} now takes some distance from elegance, and
+cowardly refuses to create an archive when @value{op-create} option is
+given, there are no arguments besides options, and @value{op-files-from}
+option is @emph{not} used. To get around the cautiousness of GNU
+@code{tar} and nevertheless create an archive with nothing in it,
+one may still use, as the value for the @value{op-files-from} option,
+a file with no names in it, as shown in the following commands:
-@item BACKUP_HOUR
-The hour at which the backups are done. This can be a number from 0
-to 23, or the string @samp{now}.
+@example
+@kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
+@kbd{tar cfT empty-archive.tar /dev/null}
+@end example
-@item TAPE_FILE
-The device @code{tar} writes the archive to. This device should be
-attached to the host on which the dump scripts are run.
-@c <<< examples for all ...
+@item @value{op-extract}
-@item TAPE_STATUS
-The command to use to obtain the status of the archive device,
-including error count. On some tape drives there may not be such a
-command; in that case, simply use `TAPE_STATUS=false'.
+A socket is stored, within a GNU @code{tar} archive, as a pipe.
-@item BLOCKING
-The blocking factor @code{tar} will use when writing the dump archive.
-@xref{Blocking Factor}.
+@item @value{op-list}
-@item BACKUP_DIRS
-A list of file systems to be dumped. You can include any directory
-name in the list---subdirectories on that file system will be
-included, regardless of how they may look to other networked machines.
-Subdirectories on other file systems will be ignored.
+GNU @code{tar} now shows dates as @samp{1996-11-09}, while it used to
+show them as @samp{Nov 11 1996}. (One can revert to the old behavior by
+defining @code{USE_OLD_CTIME} in @file{src/list.c} before reinstalling.)
+But preferrably, people you should get used to ISO 8601 dates. Local
+American dates should be made available again with full date localisation
+support, once ready. In the meantime, programs not being localisable
+for dates should prefer international dates, that's really the way to go.
-The host name specifies which host to run @code{tar} on, and should
-normally be the host that actually contains the file system. However,
-the host machine must have GNU @code{tar} installed, and must be able
-to access the directory containing the backup scripts and their
-support files using the same file name that is used on the machine
-where the scripts are run (ie. what @code{pwd} will print when in that
-directory on that machine). If the host that contains the file system
-does not have this capability, you can specify another host as long as
-it can access the file system through NFS.
+Look up @url{http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html} if you
+are curious, it contains a detailed explanation of the ISO 8601 standard.
-@item BACKUP_FILES
-A list of individual files to be dumped. These should be accessible
-from the machine on which the backup script is run.
-@c <<<same file name, be specific. through nfs ...
@end table
+@node Advanced tar, extract options, Basic tar, operations
+@section Advanced GNU @code{tar} Operations
+
+Now that you have learned the basics of using GNU @code{tar}, you may
+want to learn about further ways in which @code{tar} can help you.
+
+This chapter presents five, more advanced operations which you probably
+won't use on a daily basis, but which serve more specialized functions.
+We also explain the different styles of options and why you might want
+to use one or another, or a combination of them in your @code{tar}
+commands. Additionally, this chapter includes options which allow you to
+define the output from @code{tar} more carefully, and provide help and
+error correction in special circumstances.
+
+@FIXME{check this after the chapter is actually revised to make sure
+it still introduces the info in the chapter correctly : ).}
+
@menu
-* backup-specs example:: An Example Text of @file{Backup-specs}
-* Script Syntax:: Syntax for @file{Backup-specs}
+* Operations::
+* current state::
+* append::
+* update::
+* concatenate::
+* delete::
+* compare::
@end menu
-@node backup-specs example, Script Syntax, Backup Parameters, Backup Parameters
-@subsubsection An Example Text of @file{Backup-specs}
+@node Operations, current state, Advanced tar, Advanced tar
+@subsection The Five Advanced @code{tar} Operations
+@UNREVISED
+
+In the last chapter, you learned about the first three operations to
+@code{tar}. This chapter presents the remaining five operations to
+@code{tar}: @samp{--append}, @samp{--update}, @samp{--concatenate},
+@samp{--delete}, and @samp{--compare}.
+
+You are not likely to use these operations as frequently as those
+covered in the last chapter; however, since they perform specialized
+functions, they are quite useful when you do need to use them. We
+will give examples using the same directory and files that you created
+in the last chapter. As you may recall, the directory is called
+@file{practice}, the files are @samp{jazz}, @samp{blues}, @samp{folk},
+@samp{rock}, and the two archive files you created are
+@samp{collection.tar} and @samp{music.tar}.
+
+We will also use the archive files @samp{afiles.tar} and
+@samp{bfiles.tar}. @samp{afiles.tar} contains the members @samp{apple},
+@samp{angst}, and @samp{aspic}. @samp{bfiles.tar} contains the members
+@samp{./birds}, @samp{baboon}, and @samp{./box}.
+
+Unless we state otherwise, all practicing you do and examples you follow
+in this chapter will take place in the @file{practice} directory that
+you created in the previous chapter; see @ref{prepare for examples}.
+(Below in this section, we will remind you of the state of the examples
+where the last chapter left them.)
+
+The five operations that we will cover in this chapter are:
+
+@table @kbd
+@item --append
+@itemx -r
+Add new entries to an archive that already exists.
+@item --update
+@itemx -r
+Add more recent copies of archive members to the end of an archive, if
+they exist.
+@item --concatenate
+@itemx --catenate
+@itemx -A
+Add one or more pre-existing archives to the end of another archive.
+@item --delete
+Delete items from an archive (does not work on tapes).
+@item --compare
+@itemx --diff
+@itemx -d
+Compare archive members to their counterparts in the file system.
+@end table
-The following is the text of @file{backup-specs} as it appears at FSF:
+@node current state, append, Operations, Advanced tar
+@ifinfo
+@subsection The Current State of the Practice Files
+@end ifinfo
+
+Currently, the listing of the directory using @code{ls} is as follows:
@example
-# site-specific parameters for file system backup.
-ADMINISTRATOR=friedman
-BACKUP_HOUR=1
-TAPE_FILE=/dev/nrsmt0
-TAPE_STATUS="mts -t $TAPE_FILE"
-BLOCKING=124
-BACKUP_DIRS="
- albert:/fs/fsf
- apple-gunkies:/gd
- albert:/fs/gd2
- albert:/fs/gp
- geech:/usr/jla
- churchy:/usr/roland
- albert:/
- albert:/usr
- apple-gunkies:/
- apple-gunkies:/usr
- gnu:/hack
- gnu:/u
- apple-gunkies:/com/mailer/gnu
- apple-gunkies:/com/archive/gnu"
+@end example
-BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
+@noindent
+The archive file @samp{collection.tar} looks like this:
+
+@example
+$ @kbd{tar -tvf collection.tar}
@end example
-@node Script Syntax, , backup-specs example, Backup Parameters
-@subsubsection Syntax for @file{Backup-specs}
+@noindent
+The archive file @samp{music.tar} looks like this:
-@file{backup-specs} is in shell script syntax. The following
-conventions should be considered when editing the script:
-@c <<< "conventions?"
+@example
+$ @kbd{tar -tvf music.tar}
-A quoted string is considered to be contiguous, even if it is on more
-than one line. Therefore, you cannot include commented-out lines
-within a multi-line quoted string. BACKUP_FILES and BACKUP_DIRS are
-the two most likely parameters to be multi-line.
+@end example
-A quoted string typically cannot contain wildcards. In
-@file{backup-specs}, however, the parameters BACKUP_DIRS and
-BACKUP_FILES can contain wildcards.
+@FIXME{need to fill in the above!!!}
+
+@node append, update, current state, Advanced tar
+@subsection How to Add Files to Existing Archives: @code{--append}
+@UNREVISED
+
+If you want to add files to an existing archive, you don't need to
+create a new archive; you can use @value{op-append}. The archive must
+already exist in order to use @samp{--append}. (A related operation
+is the @samp{--update} operation; you can use this to add newer
+versions of archive members to an existing archive. To learn how to
+do this with @samp{--update}, @pxref{update}.)
+
+@FIXME{Explain in second paragraph whether you can get to the previous
+version -- explain whole situation somewhat more clearly.}
+
+If you use @value{op-append} to add a file that has the same name as an
+archive member to an archive containing that archive member, then the
+old member is not deleted. What does happen, however, is somewhat
+complex. @code{tar} @emph{allows} you to have infinite numbers of files
+with the same name. Some operations treat these same-named members no
+differently than any other set of archive members: for example, if you
+view an archive with @value{op-list}, you will see all of those members
+listed, with their modification times, owners, etc.
+
+Other operations don't deal with these members as perfectly as you might
+prefer; if you were to use @value{op-extract} to extract the archive,
+only the most recently added copy of a member with the same name as four
+other members would end up in the working directory. This is because
+@samp{--extract} extracts an archive in the order the members appeared
+in the archive; the most recently archived members will be extracted
+last. Additionally, an extracted member will @emph{overwrite} a file of
+the same name which existed in the directory already, and @code{tar}
+will not prompt you about this. Thus, only the most recently archived
+member will end up being extracted, as it will overwrite the one
+extracted before it, and so on.
+
+@FIXME{ hag -- you might want to incorporate some of the above into the
+MMwtSN node; not sure. i didn't know how to make it simpler...}
+
+There are a few ways to get around this. @FIXME-xref{Multiple Members
+with the Same Name}.
+
+@cindex Members, replacing with other members
+@cindex Replacing members with other members
+If you want to replace an archive member, use @value{op-delete} to
+delete the member you want to remove from the archive, , and then use
+@samp{--append} to add the member you want to be in the archive. Note
+that you can not change the order of the archive; the most recently
+added member will still appear last. In this sense, you cannot truely
+``replace'' one member with another. (Replacing one member with another
+will not work on certain types of media, such as tapes; see @ref{delete}
+and @ref{Media}, for more information.)
-@node Scripted Backups, Scripted Restoration, Backup Parameters, Backup Scripts
-@subsection Using the Backup Scripts
+@menu
+* appending files:: Appending Files to an Archive
+* multiple::
+@end menu
-The syntax for running a backup script is:
+@node appending files, multiple, append, append
+@subsubsection Appending Files to an Archive
+@UNREVISED
+@cindex Adding files to an Archive
+@cindex Appending files to an Archive
+@cindex Archives, Appending files to
+
+The simplest way to add a file to an already existing archive is the
+@value{op-append} operation, which writes specified files into the
+archive whether or not they are already among the archived files.
+When you use @samp{--append}, you @emph{must} specify file name
+arguments, as there is no default. If you specify a file that already
+exists in the archive, another copy of the file will be added to the
+end of the archive. As with other operations, the member names of the
+newly added files will be exactly the same as their names given on the
+command line. The @value{op-verbose} option will print out the names
+of the files as they are written into the archive.
+
+@samp{--append} cannot be performed on some tape drives, unfortunately,
+due to deficiencies in the formats those tape drives use. The archive
+must be a valid @code{tar} archive, or else the results of using this
+operation will be unpredictable. @xref{Media}.
+
+To demonstrate using @samp{--append} to add a file to an archive,
+create a file called @file{rock} in the @file{practice} directory.
+Make sure you are in the @file{practice} directory. Then, run the
+following @code{tar} command to add @file{rock} to
+@file{collection.tar}:
@example
-@file{script-name} [@var{time-to-be-run}]
+$ @kbd{tar --append --file=collection.tar rock}
@end example
-where @var{time-to-be-run} can be a specific system time, or can be
-@kbd{now}. If you do not specify a time, the script runs at the time
-specified in @file{backup-specs} (@pxref{Script Syntax}).
-
-You should start a script with a tape or disk mounted. Once you start
-a script, it prompts you for new tapes or disks as it needs them.
-Media volumes don't have to correspond to archive files---a
-multi-volume archive can be started in the middle of a tape that
-already contains the end of another multi-volume archive. The
-@code{restore} script prompts for media by its archive volume, so to
-avoid an error message you should keep track of which tape (or disk)
-contains which volume of the archive. @xref{Scripted Restoration}.
-
-@c <<<have file names changed? -ringo
-The backup scripts write two files on the file system. The first is a
-record file in @file{/etc/tar-backup/}, which is used by the scripts
-to store and retrieve information about which files were dumped. This
-file is not meant to be read by humans, and should not be deleted by
-them. @xref{incremental and listed-incremental}, for a more
-detailed explanation of this file.
+@noindent
+If you now use the @value{op-list} operation, you will see that
+@file{rock} has been added to the archive:
-The second file is a log file containing the names of the file systems
-and files dumped, what time the backup was made, and any error
-messages that were generated, as well as how much space was left in
-the media volume after the last volume of the archive was written.
-You should check this log file after every backup. The file name is
-@file{log-@var{mmm-ddd-yyyy}-level-1} or
-@file{log-@var{mmm-ddd-yyyy}-full}.
+@example
+$ @kbd{tar --list --file=collection.tar}
+-rw-rw-rw- me user 28 1996-10-18 16:31 jazz
+-rw-rw-rw- me user 21 1996-09-23 16:44 blues
+-rw-rw-rw- me user 20 1996-09-23 16:44 folk
+-rw-rw-rw- me user 20 1996-09-23 16:44 rock
+@end example
-The script also prints the name of each system being dumped to the
-standard output.
-@c <<<the section on restore scripts is commented out.
-@c <<< a section on non-scripted testore mya be a good idea
-@ignore
-@node Scripted Restoration, , Scripted Backups, Backup Scripts
-@subsection Using the Restore Script
-@c subject to change as things develop
+@FIXME{in theory, dan will (soon) try to turn this node into what it's
+title claims it will become...}
+
+@node multiple, , appending files, append
+@subsubsection Multiple Files with the Same Name
+
+You can use @value{op-append} to add copies of files which have been
+updated since the archive was created. (However, we do not recommend
+doing this since there is another @code{tar} option called
+@samp{--update}; @pxref{update} for more information. We describe this
+use of @samp{--append} here for the sake of completeness.) @FIXME{is
+this really a good idea, to give this whole description for something
+which i believe is basically a Stupid way of doing something? certain
+aspects of it show ways in which tar is more broken than i'd personally
+like to admit to, specifically the last sentence. On the other hand, i
+don't think it's a good idea to be saying that re explicitly don't
+recommend using something, but i can't see any better way to deal with
+the situation.} When you extract the archive, the older version will be
+effectively lost. This works because files are extracted from an
+archive in the order in which they were archived. Thus, when the
+archive is extracted, a file archived later in time will overwrite a
+file of the same name which was archived earlier, even though the older
+version of the file will remain in the archive unless you delete all
+versions of the file.
+
+Supposing you change the file @file{blues} and then append the changed
+version to @file{collection.tar}. As you saw above, the original
+@file{blues} is in the archive @file{collection.tar}. If you change the
+file and append the new version of the file to the archive, there will
+be two copies in the archive. When you extract the archive, the older
+version of the file will be extracted first, and then overwritten by the
+newer version when it is extracted.
+
+You can append the new, changed copy of the file @file{blues} to the
+archive in this way:
-To restore files that were archived using a scripted backup, use the
-@code{restore} script. The syntax for the script is:
+@example
+$ @kbd{tar --append --verbose --file=collection.tar blues}
+blues
+@end example
+@noindent
+Because you specified the @samp{--verbose} option, @code{tar} has
+printed the name of the file being appended as it was acted on. Now
+list the contents of the archive:
-where ##### are the file systems to restore from, and
-##### is a regular expression which specifies which files to
-restore. If you specify +all, the script restores all the files
-in the file system.
+@example
+$ @kbd{tar --list --verbose --file=collection.tar}
+-rw-rw-rw- me user 28 1996-10-18 16:31 jazz
+-rw-rw-rw- me user 21 1996-09-23 16:44 blues
+-rw-rw-rw- me user 20 1996-09-23 16:44 folk
+-rw-rw-rw- me user 20 1996-09-23 16:44 rock
+-rw-rw-rw- me user 58 1996-10-24 18:30 blues
+@end example
-You should start the restore script with the media containing the
-first volume of the archive mounted. The script will prompt for other
-volumes as they are needed. If the archive is on tape, you don't need
-to rewind the tape to to its beginning---if the tape head is
-positioned past the beginning of the archive, the script will rewind
-the tape as needed. @xref{Media}, for a discussion of tape
-positioning.
+@noindent
+The newest version of @file{blues} is now at the end of the archive
+(note the different creation dates and file sizes). If you extract
+the archive, the older version of the file @file{blues} will be
+overwritten by the newer version. You can confirm this by extracting
+the archive and running @samp{ls} on the directory. @xref{Writing},
+for more information. (@emph{Please note:} This is the case unless
+you employ the @value{op-backup} option; @FIXME-ref{Multiple Members
+with the Same Name}.)
+
+@node update, concatenate, append, Advanced tar
+@subsection Updating an Archive
+@UNREVISED
+@cindex Updating an archive
-If you specify @samp{+all} as the @var{files} argument, the
-@code{restore} script extracts all the files in the archived file
-system into the active file system.
+In the previous section, you learned how to use @value{op-append} to add
+a file to an existing archive. A related operation is
+@value{op-update}. The @samp{--update} operation updates a @code{tar}
+archive by comparing the date of the specified archive members against
+the date of the file with the same name. If the file has been modified
+more recently than the archive member, then the newer version of the
+file is added to the archive (as with @value{op-append}).
-@quotation
-@strong{Warning:}The script will delete files from the active file
-system if they were not in the file system when the archive was made.
-@end quotation
+Unfortunately, you cannot use @samp{--update} with magnetic tape drives.
+The operation will fail.
-@xref{incremental and listed-incremental}, for an explanation of how
-the script makes that determination.
-@c this may be an option, not a given
-@end ignore
+@FIXME{other examples of media on which --update will fail? need to ask
+charles and/or mib/thomas/dave shevett..}
-@node incremental and listed-incremental, Problems, Backup Scripts, Backups and Restoration
-@section The @code{+incremental} and @code{+listed-incremental} Options
+Both @samp{--update} and @samp{--append} work by adding to the end
+of the archive. When you extract a file from the archive, only the
+version stored last will wind up in the file system, unless you use
+the @value{op-backup} option (@FIXME-ref{Multiple Members with the
+Same Name}).
-@samp{+incremental} is used in conjunction with @samp{+create},
-@samp{+extract} or @samp{+list} when backing up and restoring file
-systems. An archive cannot be extracted or listed with the
-@samp{+incremental} option specified unless it was created with the
-option specified. This option should only be used by a script, not by
-the user, and is usually disregarded in favor of
-@samp{+listed-incremental}, which is described below.
+@menu
+* how to update::
+@end menu
-@samp{+incremental} in conjunction with @samp{+create} causes
-@code{tar} to write, at the beginning of the archive, an entry for
-each of the directories that will be archived. The entry for a
-directory includes a list of all the files in the directory at the
-time the archive was created and a flag for each file indicating
-whether or not the file is going to be put in the archive.
-
-Note that this option causes @code{tar} to create a non-standard
-archive that may not be readable by non-GNU versions of the @code{tar}
-program.
+@node how to update, , update, update
+@subsubsection How to Update an Archive Using @code{--update}
-@samp{+incremental} in conjunction with @samp{+extract} causes
-@code{tar} to read the lists of directory contents previously stored
-in the archive, @emph{delete} files in the file system that did not
-exist in their directories when the archive was created, and then
-extract the files in the archive.
+You must use file name arguments with the @value{op-update} operation.
+If you don't specify any files, @code{tar} won't act on any files and
+won't tell you that it didn't do anything (which may end up confusing
+you).
-This behavior is convenient when restoring a damaged file system from
-a succession of incremental backups: it restores the entire state of
-the file system to that which obtained when the backup was made. If
-@samp{+incremental} isn't specified, the file system will probably
-fill up with files that shouldn't exist any more.
+@FIXME{note: the above parenthetical added because in fact, this
+behavior just confused the author. :-) }
-@samp{+incremental} in conjunction with @samp{+list}, causes
-@code{tar} to print, for each directory in the archive, the list of
-files in that directory at the time the archive was created. This
-information is put out in a format that is not easy for humans to
-read, but which is unambiguous for a program: each file name is
-preceded by either a @samp{Y} if the file is present in the archive,
-an @samp{N} if the file is not included in the archive, or a @samp{D}
-if the file is a directory (and is included in the archive). Each
-file name is terminated by a null character. The last file is followed
-by an additional null and a newline to indicate the end of the data.
+To see the @samp{--update} option at work, create a new file,
+@file{classical}, in your practice directory, and some extra text to the
+file @file{blues}, using any text editor. Then invoke @code{tar} with
+the @samp{update} operation and the @value{op-verbose} option specified,
+using the names of all the files in the practice directory as file name
+arguments:
-@samp{+listed-incremental}=@var{file} acts like @samp{+incremental},
-but when used in conjunction with @samp{+create} will also cause
-@code{tar} to use the file @var{file}, which contains information
-about the state of the file system at the time of the last backup, to
-decide which files to include in the archive being created. That file
-will then be updated by @code{tar}. If the file @var{file} does not
-exist when this option is specified, @code{tar} will create it, and
-include all appropriate files in the archive.
+@example
+$ @kbd{tar --update -v -f collection.tar blues folk rock classical}
+blues
+classical
+$
+@end example
-The file @var{file}, which is archive independent, contains the date
-it was last modified and a list of devices, inode numbers and
-directory names. @code{tar} will archive files with newer mod dates
-or inode change times, and directories with an unchanged inode number
-and device but a changed directory name. The file is updated after
-the files to be archived are determined, but before the new archive is
-actually created.
+@noindent
+Because we have specified verbose mode, @code{tar} prints out the names
+of the files it is working on, which in this case are the names of the
+files that needed to be updated. If you run @samp{tar --list} and look
+at the archive, you will see @file{blues} and @file{classical} at its
+end. There will be a total of two versions of the member @samp{blues};
+the one at the end will be newer and larger, since you added text before
+updating it.
+
+(The reason @code{tar} does not overwrite the older file when updating
+it is because writing to the middle of a section of tape is a difficult
+process. Tapes are not designed to go backward. @xref{Media}, for more
+information about tapes.
+
+@value{op-update} is not suitable for performing backups for two
+reasons: it does not change directory content entries, and it lengthens
+the archive every time it is used. The GNU @code{tar} options intended
+specifically for backups are more efficient. If you need to run
+backups, please consult @ref{Backups}.
+
+@node concatenate, delete, update, Advanced tar
+@subsection Combining Archives with @code{--concatenate}
-@c <<< this section needs to be written
-@node Problems, , incremental and listed-incremental, Backups and Restoration
-@section Some Common Problems and their Solutions
+@cindex Adding archives to an archive
+@cindex Concatenating Archives
+Sometimes it may be convenient to add a second archive onto the end of
+an archive rather than adding individual files to the archive. To add
+one or more archives to the end of another archive, you should use the
+@value{op-concatenate} operation.
+
+To use @samp{--concatenate}, name the archives to be concatenated on the
+command line. (Nothing happens if you don't list any.) The members,
+and their member names, will be copied verbatim from those archives. If
+this causes multiple members to have the same name, it does not delete
+any members; all the members with the same name coexist. For
+information on how this affects reading the archive, @FIXME-ref{Multiple
+Members with the Same Name}.
+
+To demonstrate how @samp{--concatenate} works, create two small archives
+called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant
+files from @file{practice}:
-errors from system:
-permission denied
-no such file or directory
-not owner
+@example
+$ @kbd{tar -cvf bluesrock.tar blues rock}
+blues
+classical
+$ @kbd{tar -cvf folkjazz.tar folk jazz}
+folk
+jazz
+@end example
-errors from tar:
-directory checksum error
-header format error
+@noindent
+If you like, You can run @samp{tar --list} to make sure the archives
+contain what they are supposed to:
-errors from media/system:
-i/o error
-device busy
+@example
+$ @kbd{tar -tvf bluesrock.tar}
+-rw-rw-rw- melissa user 105 1997-01-21 19:42 blues
+-rw-rw-rw- melissa user 33 1997-01-20 15:34 rock
+$ @kbd{tar -tvf folkjazz.tar}
+-rw-rw-rw- melissa user 20 1996-09-23 16:44 folk
+-rw-rw-rw- melissa user 65 1997-01-30 14:15 jazz
+@end example
+
+We can concatenate these two archives with @code{tar}:
+
+@example
+$ @kbd{cd ..}
+$ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
+@end example
+
+If you now list the contents of the @file{bluesclass.tar}, you will see
+that now it also contains the archive members of @file{jazzfolk.tar}:
+
+@example
+$ @kbd{tar --list --file=bluesrock.tar}
+blues
+rock
+jazz
+folk
+@end example
+
+When you use @samp{--concatenate}, the source and target archives must
+already exist and must have been created using compatable format
+parameters (@FIXME-pxref{Matching Format Parameters}). The new,
+concatenated archive will be called by the same name as the first
+archive listed on the command line. @FIXME{is there a way to specify a
+new name?}
+
+Like @value{op-append}, this operation cannot be performed on some
+tape drives, due to deficiencies in the formats those tape drives use.
+
+@cindex @code{concatenate} vs @code{cat}
+@cindex @code{cat} vs @code{concatenate}
+It may seem more intuitive to you to want or try to use @code{cat} to
+concatenate two archives instead of using the @samp{--concatenate}
+operation; after all, @code{cat} is the utility for combining files.
+
+However, @code{tar} archives incorporate an end-of-file marker which
+must be removed if the concatenated archives are to be read properly as
+one archive. @samp{--concatenate} removes the end-of-archive marker
+from the target archive before each new archive is appended. If you use
+@code{cat} to combine the archives, the result will not be a valid
+@code{tar} format archive. If you need to retrieve files from an
+archive that was added to using the @code{cat} utility, use the
+@value{op-ignore-zeros} option. @xref{Ignore Zeros}, for further
+information on dealing with archives improperly combined using the
+@code{cat} shell utility.
+
+@FIXME{this shouldn't go here. where should it go?} You must specify
+the source archives using @value{op-file} (@value{pxref-file}). If you
+do not specify the target archive, @code{tar} uses the value of the
+environment variable @code{TAPE}, or, if this has not been set, the
+default archive name.
+
+@node delete, compare, concatenate, Advanced tar
+@subsection Removing Archive Members Using @samp{--delete}
+@UNREVISED
+@cindex Deleting files from an archive
+@cindex Removing files from an archive
+
+You can remove members from an archive by using the @value{op-delete}
+option. Specify the name of the archive with @value{op-file} and then
+specify the names of the members to be deleted; if you list no member
+names, nothing will be deleted. The @value{op-verbose} option will
+cause @code{tar} to print the names of the members as they are deleted.
+As with @value{op-extract}, you must give the exact member names when
+using @samp{tar --delete}. @samp{--delete} will remove all versions of
+the named file from the archive. The @samp{--delete} operation can run
+very slowly.
+
+Unlike other operations, @samp{--delete} has no short form.
+
+@cindex Tapes, using @code{--delete} and
+@cindex Deleting from tape archives
+This operation will rewrite the archive. You can only use
+@samp{--delete} on an archive if the archive device allows you to
+write to any point on the media, such as a disk; because of this, it
+does not work on magnetic tapes. Do not try to delete an archive member
+from a magnetic tape; the action will not succeed, and you will be
+likely to scramble the archive and damage your tape. There is no safe
+way (except by completely re-writing the archive) to delete files from
+most kinds of magnetic tape. @xref{Media}.
+
+To delete all versions of the file @file{blues} from the archive
+@file{collection.tar} in the @file{practice} directory, make sure you
+are in that directory, and then,
+
+@example
+$ @kbd{tar --list --file=collection.tar}
+blues
+folk
+jazz
+rock
+practice/blues
+practice/folk
+practice/jazz
+practice/rock
+practice/blues
+$ @kbd{tar --delete --file=collection.tar blues}
+$ @kbd{tar --list --file=collection.tar}
+folk
+jazz
+rock
+$
+@end example
+
+@FIXME{I changed the order of these nodes around and haven't had a chance
+to fix the above example's results, yet. I have to play with this and
+follow it and see what it actually does!}
+
+The @value{op-delete} option has been reported to work properly when
+@code{tar} acts as a filter from @code{stdin} to @code{stdout}.
+
+@node compare, , delete, Advanced tar
+@subsection Comparing Archive Members with the File System
+@cindex Verifying the currency of an archive
+@UNREVISED
+
+The @samp{--compare} (@samp{-d}), or @samp{--diff} operation compares
+specified archive members against files with the same names, and then
+reports differences in file size, mode, owner, modification date and
+contents. You should @emph{only} specify archive member names, not file
+names. If you do not name any members, then @code{tar} will compare the
+entire archive. If a file is represented in the archive but does not
+exist in the file system, @code{tar} reports a difference.
+
+You have to specify the record size of the archive when modifying an
+archive with a non-default record size.
+
+@code{tar} ignores files in the file system that do not have
+corresponding members in the archive.
+
+The following example compares the archive members @file{rock},
+@file{blues} and @file{funk} in the archive @file{bluesrock.tar} with
+files of the same name in the file system. (Note that there is no file,
+@file{funk}; @code{tar} will report an error message.)
+
+@example
+$ @kbd{tar --compare --file=bluesrock.tar rock blues funk}
+rock
+blues
+tar: funk not found in archive
+@end example
+
+@noindent
+@FIXME{what does this actually depend on? i'm making a guess,
+here.}Depending on the system where you are running @code{tar} and the
+version you are running, @code{tar} may have a different error message,
+such as:
+
+@example
+funk: does not exist
+@end example
+
+@FIXME-xref{somewhere, for more information about format parameters.
+Melissa says: such as "format variations"? But why? Clearly I don't
+get it yet; I'll deal when I get to that section.}
+
+The spirit behind the @value{op-compare} option is to check whether the
+archive represents the current state of files on disk, more than validating
+the integrity of the archive media. For this later goal, @xref{verify}.
+
+@node extract options, backup, Advanced tar, operations
+@section Options Used by @code{--extract}
+@UNREVISED
+
+@FIXME{i need to get dan to go over these options with me and see if
+there's a better way of organizing them.}
+
+The previous chapter showed how to use @value{op-extract} to extract
+an archive into the filesystem. Various options cause @code{tar} to
+extract more information than just file contents, such as the owner,
+the permissions, the modification date, and so forth. This section
+presents options to be used with @samp{--extract} when certain special
+considerations arise. You may review the information presented in
+@ref{extract} for more basic information about the
+@samp{--extract} operation.
+
+@menu
+* Reading:: Options to Help Read Archives
+* Writing:: Changing How @code{tar} Writes Files
+* Scarce:: Coping with Scarce Resources
+@end menu
+
+@node Reading, Writing, extract options, extract options
+@subsection Options to Help Read Archives
+@cindex Options when reading archives
+@cindex Reading incomplete records
+@cindex Records, incomplete
+@cindex End-of-archive entries, ignoring
+@cindex Ignoring end-of-archive entries
+@cindex Large lists of file names on small machines
+@cindex Small memory
+@cindex Running out of space
+@UNREVISED
+
+Normally, @code{tar} will request data in full record increments from
+an archive storage device. If the device cannot return a full record,
+@code{tar} will report an error. However, some devices do not always
+return full records, or do not require the last record of an archive to
+be padded out to the next record boundary. To keep reading until you
+obtain a full record, or to accept an incomplete record if it contains
+an end-of-archive marker, specify the @value{op-read-full-records} option
+in conjunction with the @value{op-extract} or @value{op-list} operations.
+@value{xref-read-full-records}.
+
+The @value{op-read-full-records} option is turned on by default when
+@code{tar} reads an archive from standard input, or from a remote
+machine. This is because on BSD Unix systems, attempting to read a
+pipe returns however much happens to be in the pipe, even if it is
+less than was requested. If this option were not enabled, @code{tar}
+would fail as soon as it read an incomplete record from the pipe.
+
+If you're not sure of the blocking factor of an archive, you can
+read the archive by specifying @value{op-read-full-records} and
+@value{op-blocking-factor}, using a blocking factor larger than what the
+archive uses. This lets you avoid having to determine the blocking factor
+of an archive. @value{xref-blocking-factor}.
+
+@menu
+* read full records::
+* Ignore Zeros::
+* Ignore Failed Read::
+@end menu
+
+@node read full records, Ignore Zeros, Reading, Reading
+@unnumberedsubsubsec Reading Full Records
+
+@FIXME{need sentence or so of intro here}
+
+@table @kbd
+@item --read-full-records
+@item -B
+Use in conjunction with @value{op-extract} to read an archive which
+contains incomplete records, or one which has a blocking factor less
+than the one specified.
+@end table
+
+@node Ignore Zeros, Ignore Failed Read, read full records, Reading
+@unnumberedsubsubsec Ignoring Blocks of Zeros
+
+Normally, @code{tar} stops reading when it encounters a block of zeros
+between file entries (which usually indicates the end of the archive).
+@value{op-ignore-zeros} allows @code{tar} to completely read an archive
+which contains a block of zeros before the end (i.e.@: a damaged
+archive, or one which was created by @code{cat}-ing several archives
+together).
+
+The @value{op-ignore-zeros} option is turned off by default because many
+versions of @code{tar} write garbage after the end-of-archive entry,
+since that part of the media is never supposed to be read. GNU
+@code{tar} does not write after the end of an archive, but seeks to
+maintain compatablity among archiving utilities.
+
+@table @kbd
+@item --ignore-zeros
+@itemx -i
+To ignore blocks of zeros (ie.@: end-of-archive entries) which may be
+encountered while reading an archive. Use in conjunction with
+@value{op-extract} or @value{op-list}.
+@end table
+
+@node Ignore Failed Read, , Ignore Zeros, Reading
+@unnumberedsubsubsec Ignore Fail Read
+
+@FIXME{Is this in the right place? It doesn't exist anywhere else in
+the book (except the appendix), and has no further explanation. For that
+matter, what does it mean?!}
+
+@table @kbd
+@item --ignore-failed-read
+Do not exit with nonzero on unreadable files or directories.
+@end table
+
+@node Writing, Scarce, Reading, extract options
+@subsection Changing How @code{tar} Writes Files
+@cindex Overwriting old files, prevention
+@cindex Protecting old files
+@cindex Modification times of extracted files
+@cindex Permissions of extracted files
+@cindex Modes of extracted files
+@cindex Writing extracted files to standard output
+@cindex Standard output, writing extracted files to
+@UNREVISED
+
+@FIXME{need to mention the brand new option, --backup}
+
+@menu
+* Prevention Overwriting::
+* Keep Old Files::
+* Unlink First::
+* Recursive Unlink::
+* Modification Times::
+* Setting Access Permissions::
+* Writing to Standard Output::
+* remove files::
+@end menu
+
+@node Prevention Overwriting, Keep Old Files, Writing, Writing
+@unnumberedsubsubsec Options to Prevent Overwriting Files
+
+Normally, @code{tar} writes extracted files into the file system without
+regard to the files already on the system; i.e., files with the same
+names as archive members are overwritten when the archive is extracted.
+If the name of a corresponding file name is a symbolic link, the file
+pointed to by the symbolic link will be overwritten instead of the
+symbolic link itself (if this is possible). Moreover, special devices,
+empty directories and even symbolic links are automatically removed if
+they are found to be on the way of the proper extraction.
+
+To prevent @code{tar} from extracting an archive member from an archive
+if doing so will overwrite a file in the file system, use
+@value{op-keep-old-files} in conjunction with @samp{--extract}. When
+this option is specified, @code{tar} will report an error stating the
+name of the files in conflict instead of overwriting the file with the
+corresponding extracted archive member.
+
+@FIXME{these two P's have problems. i don't understand what they're
+trying to talk about well enough to fix them; i may have just made them
+worse (in particular the first of the two). waiting to talk with hag.}
+
+The @value{op-unlink-first} option removes existing files, symbolic links,
+empty directories, devices, etc., @emph{prior} to extracting over them.
+In particular, using this option will prevent replacing an already existing
+symbolic link by the name of an extracted file, since the link itself
+is removed prior to the extraction, rather than the file it points to.
+On some systems, the backing store for the executable @emph{is} the
+original program text. You could use the @value{op-unlink-first} option
+to prevent segmentation violations or other woes when extracting arbitrary
+executables over currently running copies. Note that if something goes
+wrong with the extraction and you @emph{did} use this option, you might
+end up with no file at all. Without this option, if something goes wrong
+with the extraction, the existing file is not overwritten and preserved.
+
+@FIXME{huh?} If you specify the @value{op-recursive-unlink} option,
+@code{tar} removes @emph{anything} that keeps you from extracting a file
+as far as current permissions will allow it. This could include removal
+of the contents of a full directory hierarchy. For example, someone
+using this feature may be very surprised at the results when extracting
+a directory entry from the archive. This option can be dangerous; be
+very aware of what you are doing if you choose to use it.
+
+@menu
+* Keep Old Files::
+* Unlink First::
+* Recursive Unlink::
+@end menu
+
+@node Keep Old Files, Unlink First, Prevention Overwriting, Writing
+@unnumberedsubsubsec Keep Old Files
+
+@table @kbd
+@item --keep-old-files
+@itemx -k
+Do not overwrite existing files from archive. The
+@value{op-keep-old-files} option prevents @code{tar} from over-writing
+existing files with files with the same name from the archive.
+The @value{op-keep-old-files} option is meaningless with @value{op-list}.
+Prevents @code{tar} from overwriting files in the file system during
+extraction.
+@end table
+
+@node Unlink First, Recursive Unlink, Keep Old Files, Writing
+@unnumberedsubsubsec Unlink First
+
+@table @kbd
+@item --unlink-first
+@itemx -U
+Try removing files before extracting over them, instead of trying to
+overwrite them.
+@end table
+
+@node Recursive Unlink, Modification Times, Unlink First, Writing
+@unnumberedsubsubsec Recursive Unlink
+
+@table @kbd
+@item --recursive-unlink
+When this option is specified, try removing files and directory hierarchies
+before extracting over them. @emph{This is a dangerous option!}
+@end table
+
+Some people argue that GNU @code{tar} should not hesitate to overwrite
+files with other files when extracting. When extracting a @code{tar}
+archive, they expect to see a faithful copy of the state of the filesystem
+when the archive was created. It is debatable that this would always
+be a proper behaviour. For example, suppose one has an archive in
+which @file{usr/local} is a link to @file{usr/local2}. Since then,
+maybe the site removed the link and renamed the whole hierarchy from
+@file{/usr/local2} to @file{/usr/local}. Such things happen all the time.
+I guess it would not be welcome at all that GNU @code{tar} removes the
+whole hierarchy just to make room for the link to be reinstated (unless it
+@emph{also} simultaneously restores the full @file{/usr/local2}, of course!
+GNU @code{tar} is indeed able to remove a whole hierarchy to reestablish a
+symbolic link, for example, but @emph{only if} @value{op-recursive-unlink}
+is specified to allow this behaviour. In any case, single files are
+silently removed.
+
+@node Modification Times, Setting Access Permissions, Recursive Unlink, Writing
+@unnumberedsubsubsec Setting Modification Times
+
+Normally, @code{tar} sets the modification times of extracted files to
+the modification times recorded for the files in the archive, but
+limits the permissions of extracted files by the current @code{umask}
+setting.
+
+To set the modification times of extracted files to the time when
+the files were extracted, use the @value{op-touch} option in
+conjunction with @value{op-extract}.
+
+@table @kbd
+@item --touch
+@itemx -m
+Sets the modification time of extracted archive members to the time
+they were extracted, not the time recorded for them in the archive.
+Use in conjunction with @value{op-extract}.
+@end table
+
+@node Setting Access Permissions, Writing to Standard Output, Modification Times, Writing
+@unnumberedsubsubsec Setting Access Permissions
+
+To set the modes (access permissions) of extracted files to those
+recorded for those files in the archive, use @samp{--same-persmissions}
+in conjunction with the @value{op-extract} operation. @FIXME{Should be
+aliased to ignore-umask.}
+
+@table @kbd
+@item --preserve-permission
+@itemx --same-permission
+@itemx --ignore-umask
+@itemx -p
+Set modes of extracted archive members to those recorded in the
+archive, instead of current umask settings. Use in conjunction with
+@value{op-extract}.
+@end table
+
+@FIXME{Following paragraph needs to be rewritten: why doesnt' this cat
+files together, why is this useful. is it really useful with
+more than one file?}
+
+@node Writing to Standard Output, remove files, Setting Access Permissions, Writing
+@unnumberedsubsubsec Writing to Standard Output
+
+To write the extracted files to the standard output, instead of
+creating the files on the file system, use @value{op-to-stdout} in
+conjunction with @value{op-extract}. This option is useful if you are
+extracting files to send them through a pipe, and do not need to
+preserve them in the file system. If you extract multiple members,
+they appear on standard output concatenated, in the order they are
+found in the archive.
+
+@table @kbd
+@item --to-stdout
+@itemx -O
+Writes files to the standard output. Used in conjunction with
+@value{op-extract}. Extract files to standard output. When this option
+is used, instead of creating the files specified, @code{tar} writes
+the contents of the files extracted to its standard output. This may
+be useful if you are only extracting the files in order to send them
+through a pipe. This option is meaningless with @value{op-list}.
+@end table
+
+@FIXME{Why would you want to do such a thing, how are files separated on
+the standard output? is this useful with more that one file? Are
+pipes the real reason?}
+
+@node remove files, , Writing to Standard Output, Writing
+@unnumberedsubsubsec Removing Files
+
+@FIXME{the various macros in the front of the manual think that this
+option goes in this section. i have no idea; i only know it's nowhere
+else in the book...}
+
+@table @kbd
+@item --remove-files
+Remove files after adding them to the archive.
+@end table
+
+@node Scarce, , Writing, extract options
+@subsection Coping with Scarce Resources
+@cindex Middle of the archive, starting in the
+@cindex Running out of space during extraction
+@cindex Disk space, running out of
+@cindex Space on the disk, recovering from lack of
+@UNREVISED
+
+@menu
+* Starting File::
+* Same Order::
+@end menu
+
+@node Starting File, Same Order, Scarce, Scarce
+@unnumberedsubsubsec Starting File
+
+@table @kbd
+@item --starting-file=@var{name}
+@itemx -K @var{name}
+Starts an operation in the middle of an archive. Use in conjunction
+with @value{op-extract} or @value{op-list}.
+@end table
+
+If a previous attempt to extract files failed due to lack of disk
+space, you can use @value{op-starting-file} to start extracting only
+after member @var{name} of the archive. This assumes, of course, that
+there is now free space, or that you are now extracting into a
+different file system. (You could also choose to suspend @code{tar},
+remove unnecessary files from the file system, and then restart the
+same @code{tar} operation. In this case, @value{op-starting-file} is
+not necessary. @value{xref-incremental}, @value{xref-interactive},
+and @value{ref-exclude}.)
+
+@node Same Order, , Starting File, Scarce
+@unnumberedsubsubsec Same Order
+
+@table @kbd
+@item --same-order
+@itemx --preserve-order
+@itemx -s
+To process large lists of file names on machines with small amounts of
+memory. Use in conjunction with @value{op-compare},
+@value{op-list}
+or @value{op-extract}.
+@end table
+
+@FIXME{we don't need/want --preserve to exist any more (from melissa:
+ie, don't want that *version* of the option to exist, or don't want
+the option to exist in either version?}
+
+@FIXME{i think this explanation is lacking.}
+
+The @value{op-same-order} option tells @code{tar} that the list of file
+names to be listed or extracted is sorted in the same order as the
+files in the archive. This allows a large list of names to be used,
+even on a small machine that would not otherwise be able to hold all
+the names in memory at the same time. Such a sorted list can easily be
+created by running @samp{tar -t} on the archive and editing its output.
+
+This option is probably never needed on modern computer systems.
+
+@node backup, Applications, extract options, operations
+@section Backup options
+
+@cindex backup options
+
+GNU @code{tar} offers options for making backups of files before writing
+new versions. These options control the details of these backups.
+They may apply to the archive itself before it is created or rewritten,
+as well as individual extracted members. Other GNU programs (@code{cp},
+@code{install}, @code{ln}, and @code{mv}, for example) offer similar
+options.
+
+Backup options may prove unexpectedly useful when extracting archives
+containing many members having identical name, or when extracting archives
+on systems having file name limitations, making different members appear
+has having similar names through the side-effect of name truncation.
+(This is true only if we have a good scheme for truncated backup names,
+which I'm not sure at all: I suspect work is needed in this area.)
+When any existing file is backed up before being overwritten by extraction,
+then clashing files are automatically be renamed to be unique, and the
+true name is kept for only the last file of a series of clashing files.
+By using verbose mode, users may track exactly what happens.
+
+At the detail level, some decisions are still experimental, and may
+change in the future, we are waiting comments from our users. So, please
+do not learn to depend blindly on the details of the backup features.
+For example, currently, directories themselves are never renamed through
+using these options, so, extracting a file over a directory still has
+good chances to fail. Also, backup options apply to created archives,
+not only to extracted members. For created archives, backups will not
+be attempted when the archive is a block or character device, or when it
+refers to a remote file.
+
+For the sake of simplicity and efficiency, backups are made by renaming old
+files prior to creation or extraction, and not by copying. The original
+name is restored if the file creation fails. If a failure occurs after a
+partial extraction of a file, both the backup and the partially extracted
+file are kept.
+
+@table @samp
+
+@item --backup
+@opindex --backup
+@cindex backups, making
+Make backups of files that are about to be overwritten or removed.
+Without this option, the original versions are destroyed.
+
+@item --suffix=@var{suffix}
+@opindex --suffix
+@cindex backup suffix
+@vindex SIMPLE_BACKUP_SUFFIX
+Append @var{suffix} to each backup file made with @samp{-b}. If this
+option is not specified, the value of the @code{SIMPLE_BACKUP_SUFFIX}
+environment variable is used. And if @code{SIMPLE_BACKUP_SUFFIX} is not
+set, the default is @samp{~}, just as in Emacs.
+
+@item --version-control=@var{method}
+@opindex --version-control
+@vindex VERSION_CONTROL
+@cindex backup files, type made
+Use @var{method} to determine the type of backups made with @value{op-backup}.
+If this option is not specified, the value of the @code{VERSION_CONTROL}
+environment variable is used. And if @code{VERSION_CONTROL} is not set,
+the default backup type is @samp{existing}.
+
+@vindex version-control @r{Emacs variable}
+This option corresponds to the Emacs variable @samp{version-control};
+the same values for @var{method} are accepted as in Emacs. This options
+also more descriptive name. The valid @var{method}s (unique
+abbreviations are accepted):
+
+@table @samp
+@item t
+@itemx numbered
+@opindex numbered @r{backup method}
+Always make numbered backups.
+
+@item nil
+@itemx existing
+@opindex existing @r{backup method}
+Make numbered backups of files that already have them, simple backups
+of the others.
+
+@item never
+@itemx simple
+@opindex simple @r{backup method}
+Always make simple backups.
+
+@end table
+
+@end table
+
+Some people express the desire to @emph{always} use the @var{op-backup}
+option, by defining some kind of alias or script. This is not as easy
+as one may thing, due to the fact old style options should appear first
+and consume arguments a bit inpredictably for an alias or script. But,
+if you are ready to give up using old style options, you may resort to
+using something like (a Bourne shell function here):
+
+@example
+tar () @{ /usr/local/bin/tar --backup $*; @}
+@end example
+
+@node Applications, looking ahead, backup, operations
+@section Notable @code{tar} Usages
+@UNREVISED
+
+@FIXME{Using Unix file linking capability to recreate directory
+structures---linking files into one subdirectory and then
+@code{tar}ring that directory.}
+
+@FIXME{Nice hairy example using absolute-names, newer, etc.}
+
+@findex uuencode
+You can easily use archive files to transport a group of files from
+one system to another: put all relevant files into an archive on one
+computer system, transfer the archive to another system, and extract
+the contents there. The basic transfer medium might be magnetic tape,
+Internet FTP, or even electronic mail (though you must encode the
+archive with @code{uuencode} in order to transport it properly by
+mail). Both machines do not have to use the same operating system, as
+long as they both support the @code{tar} program.
+
+For example, here is how you might copy a directory's contents from
+one disk to another, while preserving the dates, modes, owners and
+link-structure of all the files therein. In this case, the transfer
+medium is a @dfn{pipe}, which is one a Unix redirection mechanism:
+
+@smallexample
+$ @kbd{cd sourcedir; tar -cf - . | (cd targetdir; tar -xf -)}
+@end smallexample
+
+@noindent
+The command also works using short option forms:
+
+@FIXME{The following using standard input/output correct??}
+@smallexample
+$ @w{@kbd{cd sourcedir; tar --create --file=- . | (cd targetdir; tar --extract --file=-)}}
+@end smallexample
+
+@noindent
+This is one of the easiest methods to transfer a @code{tar} archive.
+
+@node looking ahead, , Applications, operations
+@section Looking Ahead: The Rest of this Manual
+
+You have now seen how to use all eight of the operations available to
+@code{tar}, and a number of the possible options. The next chapter
+explains how to choose and change file and archive names, how to use
+files to store names of other files which you can then call as
+arguments to @code{tar} (this can help you save time if you expect to
+archive the same list of files a number of times), and how to
+@FIXME{in case it's not obvious, i'm making this up in some sense
+based on my imited memory of what the next chapter *really* does. i
+just wanted to flesh out this final section a little bit so i'd
+remember to sitck it in here. :-)}
+
+If there are too many files to conveniently list on the command line,
+you can list the names in a file, and @code{tar} will read that file.
+@value{xref-files-from}.
+
+There are various ways of causing @code{tar} to skip over some files,
+and not archive them. @xref{Choosing}.
+
+@node Backups, Choosing, operations, Top
+@chapter Performing Backups and Restoring Files
+@UNREVISED
+
+GNU @code{tar} is distributed along with the scripts which the Free
+Software Foundation uses for performing backups. There is no corresponding
+scripts available yet for doing restoration of files. Even if there is
+a good chance those scripts may be satisfying to you, they are not the
+only scripts or methods available for doing backups and restore. You may
+well create your own, or use more sophisticated packages dedicated to
+that purpose.
+
+Some users are enthusiastic about @code{Amanda} (The Advanced Maryland
+Automatic Network Disk Archiver), a backup system developed by James
+da Silva @file{jds@@cs.umd.edu} and available on many Unix systems.
+This is free software, and it is available at these places:
+
+@example
+http://www.cs.umd.edu/projects/amanda/amanda.html
+ftp://ftp.cs.umd.edu/pub/amanda
+@end example
+
+@ifclear PUBLISH
+
+Here is a possible plan for a future documentation about the backuping
+scripts which are provided within the GNU @code{tar} distribution.
+
+@example
+.* dumps
+. + what are dumps
+
+. + different levels of dumps
+. - full dump = dump everything
+. - level 1, level 2 dumps etc, -
+ A level n dump dumps everything changed since the last level
+ n-1 dump (?)
+
+. + how to use scripts for dumps (ie, the concept)
+. - scripts to run after editing backup specs (details)
+
+. + Backup Specs, what is it.
+. - how to customize
+. - actual text of script [/sp/dump/backup-specs]
+
+. + Problems
+. - rsh doesn't work
+. - rtape isn't installed
+. - (others?)
+
+. + the --incremental option of tar
+
+. + tapes
+. - write protection
+. - types of media
+. : different sizes and types, useful for different things
+. - files and tape marks
+ one tape mark between files, two at end.
+. - positioning the tape
+ MT writes two at end of write,
+ backspaces over one when writing again.
+@end example
+
+@end ifclear
+
+This chapter documents both the provided FSF scripts and @code{tar}
+options which are more specific to usage as a backup tool.
+
+To @dfn{back up} a file system means to create archives that contain
+all the files in that file system. Those archives can then be used to
+restore any or all of those files (for instance if a disk crashes or a
+file is accidently deleted). File system @dfn{backups} are also
+called @dfn{dumps}.
+
+@menu
+* Full Dumps:: Using @code{tar} to Perform Full Dumps
+* Inc Dumps:: Using @code{tar} to Perform Incremental Dumps
+* incremental and listed-incremental:: The Incremental Options
+* Backup Levels:: Levels of Backups
+* Backup Parameters:: Setting Parameters for Backups and Restoration
+* Scripted Backups:: Using the Backup Scripts
+* Scripted Restoration:: Using the Restore Script
+@end menu
+
+@node Full Dumps, Inc Dumps, Backups, Backups
+@section Using @code{tar} to Perform Full Dumps
+@UNREVISED
+
+@cindex full dumps
+@cindex dumps, full
+
+@cindex corrupted archives
+Full dumps should only be made when no other people or programs
+are modifying files in the filesystem. If files are modified while
+@code{tar} is making the backup, they may not be stored properly in
+the archive, in which case you won't be able to restore them if you
+have to. (Files not being modified are written with no trouble, and do
+not corrupt the entire archive.)
+
+You will want to use the @value{op-label} option to give the archive a
+volume label, so you can tell what this archive is even if the label
+falls off the tape, or anything like that.
+
+Unless the filesystem you are dumping is guaranteed to fit on
+one volume, you will need to use the @value{op-multi-volume} option.
+Make sure you have enough tapes on hand to complete the backup.
+
+If you want to dump each filesystem separately you will need to use
+the @value{op-one-file-system} option to prevent @code{tar} from crossing
+filesystem boundaries when storing (sub)directories.
+
+The @value{op-incremental} option is not needed, since this is a complete
+copy of everything in the filesystem, and a full restore from this
+backup would only be done onto a completely empty disk.
+
+Unless you are in a hurry, and trust the @code{tar} program (and your
+tapes), it is a good idea to use the @value{op-verify} option, to make
+sure your files really made it onto the dump properly. This will
+also detect cases where the file was modified while (or just after)
+it was being archived. Not all media (notably cartridge tapes) are
+capable of being verified, unfortunately.
+
+@value{op-listed-incremental} take a file name argument always. If the
+file doesn't exist, run a level zero dump, creating the file. If the
+file exists, uses that file to see what has changed.
+
+@value{op-incremental} @FIXME{look it up}
+
+@value{op-incremental} handle old GNU-format incremental backup.
+
+This option should only be used when creating an incremental backup of
+a filesystem. When the @value{op-incremental} option is used, @code{tar}
+writes, at the beginning of the archive, an entry for each of the
+directories that will be operated on. The entry for a directory
+includes a list of all the files in the directory at the time the
+dump was done, and a flag for each file indicating whether the file
+is going to be put in the archive. This information is used when
+doing a complete incremental restore.
+
+Note that this option causes @code{tar} to create a non-standard
+archive that may not be readable by non-GNU versions of the @code{tar}
+program.
+
+The @value{op-incremental} option means the archive is an incremental
+backup. Its meaning depends on the command that it modifies.
+
+If the @value{op-incremental} option is used with @value{op-list}, @code{tar}
+will list, for each directory in the archive, the list of files in
+that directory at the time the archive was created. This information
+is put out in a format that is not easy for humans to read, but which
+is unambiguous for a program: each file name is preceded by either a
+@samp{Y} if the file is present in the archive, an @samp{N} if the
+file is not included in the archive, or a @samp{D} if the file is
+a directory (and is included in the archive). Each file name is
+terminated by a null character. The last file is followed by an
+additional null and a newline to indicate the end of the data.
+
+If the @value{op-incremental} option is used with @value{op-extract}, then
+when the entry for a directory is found, all files that currently
+exist in that directory but are not listed in the archive @emph{are
+deleted from the directory}.
+
+This behavior is convenient when you are restoring a damaged file
+system from a succession of incremental backups: it restores the
+entire state of the file system to that which obtained when the backup
+was made. If you don't use @value{op-incremental}, the file system will
+probably fill up with files that shouldn't exist any more.
+
+@value{op-listed-incremental} handle new GNU-format incremental backup.
+This option handles new GNU-format incremental backup. It has much the
+same effect as @value{op-incremental}, but also the time when the dump
+is done and the list of directories dumped is written to the given
+@var{file}. When restoring, only files newer than the saved time are
+restored, and the direcotyr list is used to speed up operations.
+
+@value{op-listed-incremental} acts like @value{op-incremental}, but when
+used in conjunction with @value{op-create} will also cause @code{tar} to
+use the file @var{file}, which contains information about the state
+of the filesystem at the time of the last backup, to decide which
+files to include in the archive being created. That file will then
+be updated by @code{tar}. If the file @var{file} does not exist when
+this option is specified, @code{tar} will create it, and include all
+appropriate files in the archive.
+
+The file, which is archive independent, contains the date it was last
+modified and a list of devices, inode numbers and directory names.
+@code{tar} will archive files with newer mod dates or inode change
+times, and directories with an unchanged inode number and device but
+a changed directory name. The file is updated after the files to
+be archived are determined, but before the new archive is actually
+created.
+
+GNU @code{tar} actually writes the file twice: once before the data
+and written, and once after.
+
+@node Inc Dumps, incremental and listed-incremental, Full Dumps, Backups
+@section Using @code{tar} to Perform Incremental Dumps
+@UNREVISED
+
+@cindex incremental dumps
+@cindex dumps, incremental
+
+Performing incremental dumps is similar to performing full dumps,
+although a few more options will usually be needed.
+
+You will need to use the @samp{-N @var{date}} option to tell @code{tar}
+to only store files that have been modified since @var{date}.
+@var{date} should be the date and time of the last full/incremental
+dump.
+
+A standard scheme is to do a @emph{monthly} (full) dump once a month,
+a @emph{weekly} dump once a week of everything since the last monthly
+and a @emph{daily} every day of everything since the last (weekly or
+monthly) dump.
+
+Here is a copy of the script used to dump the filesystems of the
+machines here at the Free Software Foundation. This script is run via
+@code{cron} late at night when people are least likely to be using the
+machines. This script dumps several filesystems from several machines
+at once (via NFS). The operator is responsible for ensuring that all
+the machines will be up at the time the dump happens. If a machine is
+not running, its files will not be dumped, and the next day's
+incremental dump will @emph{not} store files that would have gone onto
+that dump.
+
+@example
+#!/bin/csh
+# Dump thingie
+set now = `date`
+set then = `cat date.nfs.dump`
+/u/hack/bin/tar -c -G -v\
+ -f /dev/rtu20\
+ -b 126\
+ -N "$then"\
+ -V "Dump from $then to $now"\
+ /alpha-bits/gp\
+ /gnu/hack\
+ /hobbes/u\
+ /spiff/u\
+ /sugar-bombs/u
+echo $now > date.nfs.dump
+mt -f /dev/rtu20 rew
+@end example
+
+Output from this script is stored in a file, for the operator to
+read later.
+
+This script uses the file @file{date.nfs.dump} to store the date/time
+of the last dump.
+
+Since this is a streaming tape drive, no attempt to verify the archive
+is done. This is also why the high blocking factor (126) is used.
+The tape drive must also be rewound by the @code{mt} command after
+the dump is made.
+
+@node incremental and listed-incremental, Backup Levels, Inc Dumps, Backups
+@section The Incremental Options
+@UNREVISED
+
+@value{op-incremental} is used in conjunction with @value{op-create},
+@value{op-extract} or @value{op-list} when backing up and restoring file
+systems. An archive cannot be extracted or listed with the
+@value{op-incremental} option specified unless it was created with the
+option specified. This option should only be used by a script, not by
+the user, and is usually disregarded in favor of
+@value{op-listed-incremental}, which is described below.
+
+@value{op-incremental} in conjunction with @value{op-create} causes
+@code{tar} to write, at the beginning of the archive, an entry for
+each of the directories that will be archived. The entry for a
+directory includes a list of all the files in the directory at the
+time the archive was created and a flag for each file indicating
+whether or not the file is going to be put in the archive.
+
+Note that this option causes @code{tar} to create a non-standard
+archive that may not be readable by non-GNU versions of the @code{tar}
+program.
+
+@value{op-incremental} in conjunction with @value{op-extract} causes
+@code{tar} to read the lists of directory contents previously stored
+in the archive, @emph{delete} files in the file system that did not
+exist in their directories when the archive was created, and then
+extract the files in the archive.
+
+This behavior is convenient when restoring a damaged file system from
+a succession of incremental backups: it restores the entire state of
+the file system to that which obtained when the backup was made. If
+@value{op-incremental} isn't specified, the file system will probably
+fill up with files that shouldn't exist any more.
+
+@value{op-incremental} in conjunction with @value{op-list}, causes
+@code{tar} to print, for each directory in the archive, the list of
+files in that directory at the time the archive was created. This
+information is put out in a format that is not easy for humans to
+read, but which is unambiguous for a program: each file name is
+preceded by either a @samp{Y} if the file is present in the archive,
+an @samp{N} if the file is not included in the archive, or a @samp{D}
+if the file is a directory (and is included in the archive). Each
+file name is terminated by a null character. The last file is followed
+by an additional null and a newline to indicate the end of the data.
+
+@value{op-listed-incremental} acts like @value{op-incremental}, but when
+used in conjunction with @value{op-create} will also cause @code{tar}
+to use the file @var{snapshot-file}, which contains information about
+the state of the file system at the time of the last backup, to decide
+which files to include in the archive being created. That file will
+then be updated by @code{tar}. If the file @var{file} does not exist
+when this option is specified, @code{tar} will create it, and include
+all appropriate files in the archive.
+
+The file @var{file}, which is archive independent, contains the date
+it was last modified and a list of devices, inode numbers and
+directory names. @code{tar} will archive files with newer mod dates
+or inode change times, and directories with an unchanged inode number
+and device but a changed directory name. The file is updated after
+the files to be archived are determined, but before the new archive is
+actually created.
+
+Despite it should be obvious that a device has a non-volatile value, NFS
+devices have non-dependable values when an automounter gets in the picture.
+This led to a great deal of spurious redumping in incremental dumps,
+so it is somewhat useless to compare two NFS devices numbers over time.
+So @code{tar} now considers all NFS devices as being equal when it comes
+to comparing directories; this is fairly gross, but there does not seem
+to be a better way to go.
+
+@FIXME{this section needs to be written}
+
+@node Backup Levels, Backup Parameters, incremental and listed-incremental, Backups
+@section Levels of Backups
+@UNREVISED
+
+An archive containing all the files in the file system is called a
+@dfn{full backup} or @dfn{full dump}. You could insure your data by
+creating a full dump every day. This strategy, however, would waste a
+substantial amount of archive media and user time, as unchanged files
+are daily re-archived.
+
+It is more efficient to do a full dump only occasionally. To back up
+files between full dumps, you can a incremental dump. A @dfn{level
+one} dump archives all the files that have changed since the last full
+dump.
+
+A typical dump strategy would be to perform a full dump once a week,
+and a level one dump once a day. This means some versions of files
+will in fact be archived more than once, but this dump strategy makes
+it possible to restore a file system to within one day of accuracy by
+only extracting two archives---the last weekly (full) dump and the
+last daily (level one) dump. The only information lost would be in
+files changed or created since the last daily backup. (Doing dumps
+more than once a day is usually not worth the trouble).
+
+GNU @code{tar} comes with scripts you can use to do full and level-one
+dumps. Using scripts (shell programs) to perform backups and
+restoration is a convenient and reliable alternative to typing out
+file name lists and @code{tar} commands by hand.
+
+Before you use these scripts, you need to edit the file
+@file{backup-specs}, which specifies parameters used by the backup
+scripts and by the restore script. @FIXME{There is no such restore
+script!}. @FIXME-xref{Script Syntax}. Once the backup parameters
+are set, you can perform backups or restoration by running the
+appropriate script.
+
+The name of the restore script is @code{restore}. @FIXME{There is
+no such restore script!}. The names of the level one and full backup
+scripts are, respectively, @code{level-1} and @code{level-0}.
+The @code{level-0} script also exists under the name @code{weekly}, and
+the @code{level-1} under the name @code{daily}---these additional names
+can be changed according to your backup schedule. @FIXME-xref{Scripted
+Restoration}, for more information on running the restoration script.
+@FIXME-xref{Scripted Backups}, for more information on running the
+backup scripts.
+
+@emph{Please Note:} The backup scripts and the restoration scripts are
+designed to be used together. While it is possible to restore files by
+hand from an archive which was created using a backup script, and to create
+an archive by hand which could then be extracted using the restore script,
+it is easier to use the scripts. @FIXME{There is no such restore script!}.
+@value{xref-incremental}, and @value{xref-listed-incremental},
+before making such an attempt.
+
+@FIXME{shorten node names}
+
+@node Backup Parameters, Scripted Backups, Backup Levels, Backups
+@section Setting Parameters for Backups and Restoration
+@UNREVISED
+
+The file @file{backup-specs} specifies backup parameters for the
+backup and restoration scripts provided with @code{tar}. You must
+edit @file{backup-specs} to fit your system configuration and schedule
+before using these scripts.
+
+@FIXME{This about backup scripts needs to be written: BS is a shell
+script .... thus ... @file{backup-specs} is in shell script syntax.}
+
+@FIXME-xref{Script Syntax}, for an explanation of this syntax.
+
+@FIXME{Whats a parameter .... looked at by the backup scripts
+... which will be expecting to find ... now syntax ... value is linked
+to lame ... @file{backup-specs} specifies the following parameters:}
+
+@table @samp
+@item ADMINISTRATOR
+The user name of the backup administrator.
+
+@item BACKUP_HOUR
+The hour at which the backups are done. This can be a number from 0
+to 23, or the string @samp{now}.
+
+@item TAPE_FILE
+The device @code{tar} writes the archive to. This device should be
+attached to the host on which the dump scripts are run.
+
+@FIXME{examples for all ...}
+
+@item TAPE_STATUS
+The command to use to obtain the status of the archive device,
+including error count. On some tape drives there may not be such a
+command; in that case, simply use `TAPE_STATUS=false'.
+
+@item BLOCKING
+The blocking factor @code{tar} will use when writing the dump archive.
+@value{xref-blocking-factor}.
+
+@item BACKUP_DIRS
+A list of file systems to be dumped. You can include any directory
+name in the list---subdirectories on that file system will be
+included, regardless of how they may look to other networked machines.
+Subdirectories on other file systems will be ignored.
+
+The host name specifies which host to run @code{tar} on, and should
+normally be the host that actually contains the file system. However,
+the host machine must have GNU @code{tar} installed, and must be able
+to access the directory containing the backup scripts and their
+support files using the same file name that is used on the machine
+where the scripts are run (ie. what @code{pwd} will print when in that
+directory on that machine). If the host that contains the file system
+does not have this capability, you can specify another host as long as
+it can access the file system through NFS.
+
+@item BACKUP_FILES
+A list of individual files to be dumped. These should be accessible
+from the machine on which the backup script is run.
+
+@FIXME{Same file name, be specific. Through NFS ...}
+
+@end table
+
+@menu
+* backup-specs example:: An Example Text of @file{Backup-specs}
+* Script Syntax:: Syntax for @file{Backup-specs}
+@end menu
+
+@node backup-specs example, Script Syntax, Backup Parameters, Backup Parameters
+@subsection An Example Text of @file{Backup-specs}
+@UNREVISED
+
+The following is the text of @file{backup-specs} as it appears at FSF:
+
+@example
+# site-specific parameters for file system backup.
+
+ADMINISTRATOR=friedman
+BACKUP_HOUR=1
+TAPE_FILE=/dev/nrsmt0
+TAPE_STATUS="mts -t $TAPE_FILE"
+BLOCKING=124
+BACKUP_DIRS="
+ albert:/fs/fsf
+ apple-gunkies:/gd
+ albert:/fs/gd2
+ albert:/fs/gp
+ geech:/usr/jla
+ churchy:/usr/roland
+ albert:/
+ albert:/usr
+ apple-gunkies:/
+ apple-gunkies:/usr
+ gnu:/hack
+ gnu:/u
+ apple-gunkies:/com/mailer/gnu
+ apple-gunkies:/com/archive/gnu"
+
+BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
+
+@end example
+
+@node Script Syntax, , backup-specs example, Backup Parameters
+@subsection Syntax for @file{Backup-specs}
+@UNREVISED
+
+@file{backup-specs} is in shell script syntax. The following
+conventions should be considered when editing the script:
+@FIXME{"conventions?"}
+
+A quoted string is considered to be contiguous, even if it is on more
+than one line. Therefore, you cannot include commented-out lines
+within a multi-line quoted string. BACKUP_FILES and BACKUP_DIRS are
+the two most likely parameters to be multi-line.
+
+A quoted string typically cannot contain wildcards. In
+@file{backup-specs}, however, the parameters BACKUP_DIRS and
+BACKUP_FILES can contain wildcards.
+
+@node Scripted Backups, Scripted Restoration, Backup Parameters, Backups
+@section Using the Backup Scripts
+@UNREVISED
+
+The syntax for running a backup script is:
+
+@example
+@file{script-name} [@var{time-to-be-run}]
+@end example
+
+where @var{time-to-be-run} can be a specific system time, or can be
+@kbd{now}. If you do not specify a time, the script runs at the time
+specified in @file{backup-specs} (@FIXME-pxref{Script Syntax}).
+
+You should start a script with a tape or disk mounted. Once you
+start a script, it prompts you for new tapes or disks as it
+needs them. Media volumes don't have to correspond to archive
+files---a multi-volume archive can be started in the middle of a
+tape that already contains the end of another multi-volume archive.
+The @code{restore} script prompts for media by its archive volume,
+so to avoid an error message you should keep track of which tape
+(or disk) contains which volume of the archive. @FIXME{There is
+no such restore script!}. @FIXME-xref{Scripted Restoration}.
+@FIXME{Have file names changed?}
+
+The backup scripts write two files on the file system. The first is a
+record file in @file{/etc/tar-backup/}, which is used by the scripts
+to store and retrieve information about which files were dumped. This
+file is not meant to be read by humans, and should not be deleted by
+them. @FIXME-xref{incremental and listed-incremental}, for a more
+detailed explanation of this file.
+
+The second file is a log file containing the names of the file systems
+and files dumped, what time the backup was made, and any error
+messages that were generated, as well as how much space was left in
+the media volume after the last volume of the archive was written.
+You should check this log file after every backup. The file name is
+@file{log-@var{mmm-ddd-yyyy}-level-1} or
+@file{log-@var{mmm-ddd-yyyy}-full}.
+
+The script also prints the name of each system being dumped to the
+standard output.
+
+@node Scripted Restoration, , Scripted Backups, Backups
+@section Using the Restore Script
+@UNREVISED
+
+@ifset PUBLISH
+
+The @code{tar} distribution does not provide restoring scripts.
+
+@end ifset
+
+@ifclear PUBLISH
+
+@quotation
+@strong{Warning:} The GNU @code{tar} distribution does @emph{not}
+provide any such @code{restore} script yet. This section is only
+listed here for documentation maintenance purposes. In any case,
+all contents is subject to change as things develop.
+@end quotation
+
+@FIXME{A section on non-scripted restore may be a good idea.}
+
+To restore files that were archived using a scripted backup, use the
+@code{restore} script. The syntax for the script is:
+
+where ***** are the file systems to restore from, and
+***** is a regular expression which specifies which files to
+restore. If you specify --all, the script restores all the files
+in the file system.
+
+You should start the restore script with the media containing the
+first volume of the archive mounted. The script will prompt for other
+volumes as they are needed. If the archive is on tape, you don't need
+to rewind the tape to to its beginning---if the tape head is
+positioned past the beginning of the archive, the script will rewind
+the tape as needed. @FIXME-xref{Media}, for a discussion of tape
+positioning.
+
+If you specify @samp{--all} as the @var{files} argument, the
+@code{restore} script extracts all the files in the archived file
+system into the active file system.
+
+@quotation
+@strong{Warning:} The script will delete files from the active file
+system if they were not in the file system when the archive was made.
+@end quotation
+
+@value{xref-incremental}, and @value{ref-listed-incremental},
+for an explanation of how the script makes that determination.
+
+@FIXME{this may be an option, not a given}
+
+@end ifclear
+
+@node Choosing, Date input formats, Backups, Top
+@chapter Choosing Files and Names for @code{tar}
+@UNREVISED
+
+@FIXME{Melissa (still) Doesn't Really Like This ``Intro'' Paragraph!!!}
+
+Certain options to @code{tar} enable you to specify a name for your
+archive. Other options let you decide which files to include or exclude
+from the archive, based on when or whether files were modified, whether
+the file names do or don't match specified patterns, or whether files
+are in specified directories.
+
+@menu
+* file:: Choosing the Archive's Name
+* Selecting Archive Members::
+* files:: Reading Names from a File
+* exclude:: Excluding Some Files
+* Wildcards::
+* after:: Operating Only on New Files
+* recurse:: Descending into Directories
+* one:: Crossing Filesystem Boundaries
+@end menu
+
+@node file, Selecting Archive Members, Choosing, Choosing
+@section Choosing and Naming Archive Files
+@cindex Naming an archive
+@cindex Archive Name
+@cindex Directing output
+@cindex Choosing an archive file
+@cindex Where is the archive?
+@UNREVISED
+
+@FIXME{should the title of this section actually be, "naming an
+archive"?}
+
+By default, @code{tar} uses an archive file name that was compiled when
+it was built on the system; usually this name refers to some physical
+tape drive on the machine. However, the person who installed @code{tar}
+on the system may not set the default to a meaningful value as far as
+most users are concerned. As a result, you will usually want to tell
+@code{tar} where to find (or create) the archive. The @value{op-file}
+option allows you to either specify or name a file to use as the archive
+instead of the default archive file location.
+
+@table @kbd
+@item --file=@var{archive-name}
+@itemx -f @var{archive-name}
+Name the archive to create or operate on. Use in conjunction with
+any operation.
+@end table
+
+For example, in this @code{tar} command,
+
+@example
+$ @kbd{tar -cvf collection.tar blues folk jazz}
+@end example
+
+@noindent
+@file{collection.tar} is the name of the archive. It must directly
+follow the @samp{-f} option, since whatever directly follows @samp{-f}
+@emph{will} end up naming the archive. If you neglect to specify an
+archive name, you may end up overwriting a file in the working directory
+with the archive you create since @code{tar} will use this file's name
+for the archive name.
+
+An archive can be saved as a file in the file system, sent through a
+pipe or over a network, or written to an I/O device such as a tape,
+floppy disk, or CD write drive.
+
+@cindex Writing new archives
+@cindex Archive creation
+If you do not name the archive, @code{tar} uses the value of the
+environment variable @code{TAPE} as the file name for the archive. If
+that is not available, @code{tar} uses a default, compiled-in archive
+name, usually that for tape unit zero (ie. @file{/dev/tu00}).
+@code{tar} always needs an archive name.
+
+If you use @file{-} as an @var{archive-name}, @code{tar} reads the
+archive from standard input (when listing or extracting files), or
+writes it to standard output (when creating an archive). If you use
+@file{-} as an @var{archive-name} when modifying an archive,
+@code{tar} reads the original archive from its standard input and
+writes the entire new archive to its standard output.
+
+@FIXME{might want a different example here; this is already used in
+"notable tar usages".}
+
+@example
+$ @kbd{cd sourcedir; tar -cf - . | (cd targetdir; tar -xf -)}
+@end example
+
+@FIXME{help!}
+
+@cindex Standard input and output
+@cindex tar to standard input and output
+To specify an archive file on a device attached to a remote machine,
+use the following:
+
+@example
+@kbd{--file=@var{hostname}:/@var{dev}/@var{file name}}
+@end example
+
+@noindent
+@code{tar} will complete the remote connection, if possible, and
+prompt you for a username and password. If you use
+@samp{--file=@@@var{hostname}:/@var{dev}/@var{file name}}, @code{tar}
+will complete the remote connection, if possible, using your username
+as the username on the remote machine.
+
+If the archive file name includes a colon (@samp{:}), then it is assumed
+to be a file on another machine. If the archive file is
+@samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the
+host @var{host}. The remote host is accessed using the @code{rsh}
+program, with a username of @var{user}. If the username is omitted
+(along with the @samp{@@} sign), then your user name will be used.
+(This is the normal @code{rsh} behavior.) It is necessary for the
+remote machine, in addition to permitting your @code{rsh} access, to
+have the @file{/usr/ucb/rmt} program installed. If you need to use a
+file whose name includes a colon, then the remote tape drive behavior
+can be inhibited by using the @value{op-force-local} option.
+
+@FIXME{i know we went over this yesterday, but bob (and now i do again,
+too) thinks it's out of the middle of nowhere. it doesn't seem to tie
+into what came before it well enough <<i moved it now, is it better
+here?>>. bob also comments that if Amanda isn't free software, we
+shouldn't mention it..}
+
+When the archive is being created to @file{/dev/null}, GNU @code{tar}
+tries to minimize input and output operations. The Amanda backup
+system, when used with GNU @code{tar}, has an initial sizing pass which
+uses this feature.
+
+@node Selecting Archive Members, files, file, Choosing
+@section Selecting Archive Members
+@cindex Specifying files to act on
+@cindex Specifying archive members
+
+@dfn{File Name arguments} specify which files in the file system
+@code{tar} operates on, when creating or adding to an archive, or which
+archive members @code{tar} operates on, when reading or deleting from
+an archive. @xref{Operations}.
+
+To specify file names, you can include them as the last arguments on
+the command line, as follows:
+@smallexample
+@kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}]
+@end smallexample
+
+If you specify a directory name as a file name argument, all the files
+in that directory are operated on by @code{tar}.
+
+If you do not specify files when @code{tar} is invoked with
+@value{op-create}, @code{tar} operates on all the non-directory files in
+the working directory. If you specify either @value{op-list} or
+@value{op-extract}, @code{tar} operates on all the archive members in the
+archive. If you specify any operation other than one of these three,
+@code{tar} does nothing.
+
+By default, @code{tar} takes file names from the command line. However,
+there are other ways to specify file or member names, or to modify the
+manner in which @code{tar} selects the files or members upon which to
+operate; @FIXME{add xref here}. In general, these methods work both for
+specifying the names of files and archive members.
+
+@node files, exclude, Selecting Archive Members, Choosing
+@section Reading Names from a File
+@UNREVISED
+
+@cindex Reading file names from a file
+@cindex Lists of file names
+@cindex File Name arguments, alternatives
+Instead of giving the names of files or archive members on the command
+line, you can put the names into a file, and then use the
+@value{op-files-from} option to @code{tar}. Give the name of the file
+which contains the list of files to include as the argument to
+@samp{--files-from}. In the list, the file names should be separated by
+newlines. You will frequently use this option when you have generated
+the list of files to archive with the @code{find} utility.
+
+@table @kbd
+@item --files-from=@var{file name}
+@itemx -T @var{file name}
+Get names to extract or create from file @var{file name}.
+@end table
+
+If you give a single dash as a file name for @samp{--files-from}, (i.e.,
+you specify either @samp{--files-from=-} or @samp{-T -}), then the file
+names are read from standard input.
+
+Unless you are running @code{tar} with @samp{--create}, you can not use
+both @samp{--files-from=-} and @samp{--file=-} (@samp{-f -}) in the same
+command.
+
+@FIXME{add bob's example, from his message on 2-10-97}
+
+The following example shows how to use @code{find} to generate a list of
+files smaller than 400K in length and put that list into a file
+called @file{small-files}. You can then use the @samp{-T} option to
+@code{tar} to specify the files from that file, @file{small-files}, to
+create the archive @file{little.tgz}. (The @samp{-z} option to
+@code{tar} compresses the archive with @code{gzip}; @pxref{gzip} for
+more information.)
+
+@example
+$ @kbd{find . -size -400 -print > small-files}
+$ @kbd{tar -c -v -z -T small-files -f little.tgz}
+@end example
+
+@noindent
+@FIXME{say more here to conclude the example/section?}
+
+@menu
+* nul::
+@end menu
+
+@node nul, , files, files
+@ifinfo
+@unnumberedsubsec @kbd{NUL} Terminated File Names
+@end ifinfo
+
+@cindex File names, terminated by @kbd{NUL}
+@cindex @kbd{NUL} terminated file names
+The @value{op-null} option causes @value{op-files-from} to read file
+names terminated by a @code{NUL} instead of a newline, so files whose
+names contain newlines can be archived using @samp{--files-from}.
+
+@table @kbd
+@item --null
+Only consider @kbd{NUL} terminated file names, instead of files that
+terminate in a newline.
+@end table
+
+The @samp{--null} option is just like the one in GNU @code{xargs} and
+@code{cpio}, and is useful with the @samp{-print0} predicate of GNU
+@code{find}. In @code{tar}, @samp{--null} also causes
+@value{op-directory} options to be treated as file names to archive, in
+case there are any files out there called @file{-C}.
+
+This example shows how to use @code{find} to generate a list of files
+larger than 800K in length and put that list into a file called
+@file{long-files}. The @samp{-print0} option to @code{find} just just
+like @samp{-print}, except that it separates files with a @kbd{NUL}
+rather than with a newline. You can then run @code{tar} with both the
+@samp{--null} and @samp{-T} options to specify that @code{tar} get the
+files from that file, @file{long-files}, to create the archive
+@file{big.tgz}. The @samp{--null} option to @code{tar} will cause
+@code{tar} to recognize the @kbd{NUL} separator between files.
+
+@example
+$ @kbd{find . -size +800 -print0 > long-files}
+$ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
+@end example
+
+@FIXME{say anything else here to conclude the section?}
+
+@node exclude, Wildcards, files, Choosing
+@section Excluding Some Files
+@cindex File names, excluding files by
+@cindex Excluding files by name and pattern
+@cindex Excluding files by file system
+@UNREVISED
+
+To avoid operating on files whose names match a particular pattern,
+use the @value{op-exclude} or @value{op-exclude-from} options.
+
+@table @kbd
+@item --exclude=@var{pattern}
+Causes @code{tar} to ignore files that match the @var{pattern}.
+@end table
+
+@findex exclude
+The @value{op-exclude} option will prevent any file or member which
+matches the shell wildcards (@var{pattern}) from being operated on
+(@var{pattern} can be a single file name or a more complex expression).
+For example, if you want to create an archive with all the contents of
+@file{/tmp} except the file @file{/tmp/foo}, you can use the command
+@samp{tar --create --file=arch.tar --exclude=foo}. You may give
+multiple @samp{--exclude} options.
+
+@table @kbd
+@item --exclude-from=@var{file}
+@itemx -X @var{file}
+Causes @code{tar} to ignore files that match the patterns listed in
+@var{file}.
+@end table
+
+@findex exclude-from
+Use the @samp{--exclude-from=@var{file-of-patterns}} option to read a
+list of shell wildcards, one per line, from @var{file}; @code{tar} will
+ignore files matching those regular expressions. Thus if @code{tar} is
+called as @w{@samp{tar -c -X foo .}} and the file @file{foo} contains a
+single line @file{*.o}, no files whose names end in @file{.o} will be
+added to the archive.
+
+@FIXME{do the exclude options files need to have stuff separated by
+newlines the same as the files-from option does?}
+
+@menu
+* problems with exclude::
+@end menu
+
+@node problems with exclude, , exclude, exclude
+@unnumberedsubsec Problems with Using the @code{exclude} Options
+
+@FIXME{put in for the editor's/editors' amusement, but should be taken
+out in the final draft, just in case! : }
+
+@ignore
+subtitled: getting screwed using exclewed
+@end ignore
+
+Some users find @samp{exclude} options confusing. Here are some common
+pitfalls:
+
+@itemize @bullet
+@item
+The main operating mode of @code{tar} will always act on file names
+listed on the command line, no matter whether or not there is an
+exclusion which would otherwise affect them. In the example above, if
+you create an archive and exclude files that end with @samp{*.o}, but
+explicitly name the file @samp{catc.o} after all the options have been
+listed, @samp{catc.o} @emph{will} be included in the archive.
+
+@item
+You can sometimes confuse the meanings of @value{op-exclude} and
+@value{op-exclude-from}. Be careful: use @value{op-exclude} when files
+to be excluded are given as a pattern on the command line. Use
+@samp{--exclude-from=@var{file-of-patterns}} to introduce the name of a
+file which contains a list of patterns, one per line; each of these
+patterns can exclude zero, one, or many files.
+
+@item
+When you use @value{op-exclude}, be sure to quote the @var{pattern}
+parameter, so GNU @code{tar} sees wildcard characters like @samp{*}.
+If you do not do this, the shell might expand the @samp{*} itself
+using files at hand, so @code{tar} might receive a list of files
+instead of one pattern, or none at all, making the command somewhat
+illegal. This might not correspond to what you want.
+
+For example, write:
+
+@example
+$ @kbd{tar -c -f @var{archive.tar} -X '*/tmp/*' @var{directory}}
+@end example
+
+@noindent
+rather than:
+
+@example
+$ @kbd{tar -c -f @var{archive.tar} -X */tmp/* @var{directory}}
+@end example
+
+@item
+You must use use shell syntax, or globbing, rather than @code{regexp}
+syntax, when using exclude options in @code{tar}. If you try to use
+@code{regexp} syntax to describe files to be excluded, your command
+might fail.
+
+@item
+In earlier versions of @code{tar}, what is now the
+@samp{--exclude-from=@var{file-of-patterns}} option was called
+@samp{--exclude-@var{pattern}} instead. Now,
+@samp{--exclude=@var{pattern}} applies to patterns listed on the command
+line and @samp{--exclude-from=@var{file-of-patterns}} applies to
+patterns listed in a file.
+
+@end itemize
+
+@node Wildcards, after, exclude, Choosing
+@section Wildcards Patterns and Matching
+
+@dfn{Globbing} is the operation by which @dfn{wildcard} characters,
+@samp{*} or @samp{?} for example, are replaced and expanded into all
+existing files matching the given pattern. However, @code{tar} often
+uses wildcard patterns for matching (or globbing) archive members instead
+of actual files in the filesystem. Wildcard patterns are also used for
+verifying volume labels of @code{tar} archives. This section has the
+purpose of explaining wildcard syntax for @code{tar}.
+
+@FIXME{the next few paragraphs need work.}
+
+A @var{pattern} should be written according to shell syntax, using wildcard
+characters to effect globbing. Most characters in the pattern stand
+for themselves in the matched string, and case is significant: @samp{a}
+will match only @samp{a}, and not @samp{A}. The character @samp{?} in the
+pattern matches any single character in the matched string. The character
+@samp{*} in the pattern matches zero, one, or more single characters in
+the matched string. The character @samp{\} says to take the following
+character of the pattern @emph{literally}; it is useful when one needs to
+match the @samp{?}, @samp{*}, @samp{[} or @samp{\} characters, themselves.
+
+The character @samp{[}, up to the matching @samp{]}, introduces a character
+class. A @dfn{character class} is a list of acceptable characters
+for the next single character of the matched string. For example,
+@samp{[abcde]} would match any of the first five letters of the alphabet.
+Note that within a character class, all of the ``special characters''
+listed above other than @samp{\} lose their special meaning; for example,
+@samp{[-\\[*?]]} would match any of the characters, @samp{-}, @samp{\},
+@samp{[}, @samp{*}, @samp{?}, or @samp{]}. (Due to parsing constraints,
+the characters @samp{-} and @samp{]} must either come @emph{first} or
+@emph{last} in a character class.)
+
+@cindex Excluding characters from a character class
+@cindex Character class, excluding characters from
+If the first character of the class after the opening @samp{[}
+is @samp{!} or @samp{^}, then the meaning of the class is reversed.
+Rather than listing character to match, it lists those characters which
+are @emph{forbidden} as the next single character of the matched string.
+
+Other characters of the class stand for themselves. The special
+construction @samp{[@var{a}-@var{e}]}, using an hyphen between two
+letters, is meant to represent all characters between @var{a} and
+@var{e}, inclusive.
+
+@FIXME{need to add a sentence or so here to make this clear for those
+who don't have dan around.}
+
+Periods (@samp{.}) or forward slashes (@samp{/}) are not considered
+special for wildcard matches. However, if a pattern completely matches
+a directory prefix of a matched string, then it matches the full matched
+string: excluding a directory also excludes all the files beneath it.
+
+There are some discussions floating in the air and asking for modifications
+in the way GNU @code{tar} accomplishes wildcard matches. We perceive
+any change of semantics in this area as a delicate thing to impose on
+GNU @code{tar} users. On the other hand, the GNU project should be
+progressive enough to correct any ill design: compatibility at all price
+is not always a good attitude. In conclusion, it is @emph{possible}
+that slight amendments be later brought to the previous description.
+Your opinions on the matter are welcome.
+
+@node after, recurse, Wildcards, Choosing
+@section Operating Only on New Files
+@cindex Excluding file by age
+@cindex Modification time, excluding files by
+@cindex Age, excluding files by
+@UNREVISED
+
+The @value{op-after-date} option causes @code{tar} to only work on files
+whose modification or inode-changed times are newer than the @var{date}
+given. If you use this option when creating or appending to an archive,
+the archive will only include new files. If you use @samp{--after-date}
+when extracting an archive, @code{tar} will only extract files newer
+than the @var{date} you specify.
+
+If you only want @code{tar} to make the date comparison based on
+modification of the actual contents of the file (rather than inode
+changes), then use the @value{op-newer-mtime} option.
+
+You may use these options with any operation. Note that these options
+differ from the @value{op-update} operation in that they allow you to
+specify a particular date against which @code{tar} can compare when
+deciding whether or not to archive the files.
+
+@table @kbd
+@item --after-date=@var{date}
+@itemx --newer=@var{date}
+@itemx -N @var{date}
+Only store files newer than @var{date}.
+
+Acts on files only if their modification or inode-changed times are
+later than @var{date}. Use in conjunction with any operation.
+
+@item --newer-mtime=@var{date}
+Acts like @value{op-after-date}, but only looks at modification times.
+@end table
+
+These options limit @code{tar} to only operating on files which have
+been modified after the date specified. A file is considered to have
+changed if the contents have been modified, or if the owner,
+permissions, and so forth, have been changed. (For more information on
+how to specify a date, see @ref{Date input formats}; remember that the
+entire date argument must be quoted if it contains any spaces.)
+
+Gurus would say that @value{op-after-date} tests both the @code{mtime}
+(time the contents of the file were last modified) and @code{ctime}
+(time the file's status was last changed: owner, permissions, etc)
+fields, while @value{op-newer-mtime} tests only @code{mtime} field.
+
+To be precise, @value{op-after-date} checks @emph{both} @code{mtime} and
+@code{ctime} and processes the file if either one is more recent than
+@var{date}, while @value{op-newer-mtime} only checks @code{mtime} and
+disregards @code{ctime}. Neither uses @code{atime} (the last time the
+contents of the file were looked at).
+
+Date specifiers can have embedded spaces. Because of this, you may need
+to quote date arguments to keep the shell from parsing them as separate
+arguments.
+
+@FIXME{Need example of --newer-mtime with quoted argument.}
+
+@quotation
+@strong{Please Note:} @value{op-after-date} and @value{op-newer-mtime}
+should not be used for incremental backups. Some files (such as those
+in renamed directories) are not selected properly by these options.
+@xref{incremental and listed-incremental}.
+@end quotation
+
+To select files newer than the modification time of a file that already
+exists, you can use the @samp{--reference} (@samp{-r}) option of GNU
+@code{date}, available in GNU shell utilities 1.13 or later. It returns
+the timestamp of that already existing file; this timestamp expands to
+become the referent date which @samp{--newer} uses to determine which
+files to archive. For example, you could say,
+
+@example
+$ @kbd{tar -cf @var{archive.tar} --newer="`date -r @var{file}`" /home}
+@end example
+
+@noindent
+which tells @FIXME{need to fill this in!}.
+
+@node recurse, one, after, Choosing
+@section Descending into Directories
+@cindex Avoiding recursion in directories
+@cindex Descending directories, avoiding
+@cindex Directories, avoiding recursion
+@cindex Recursion in directories, avoiding
+@UNREVISED
+
+@FIXME{arrggh! this is still somewhat confusing to me. :-< }
+
+@FIXME{show dan bob's comments, from 2-10-97}
+
+Usually, @code{tar} will recursively explore all directories (either
+those given on the command line or through the @value{op-files-from}
+option) for the various files they contain. However, you may not always
+want @code{tar} to act this way.
+
+The @value{op-no-recursion} option inhibits @code{tar}'s recursive descent
+into specified directories. If you specify @samp{--no-recursion}, you can
+use the @code{find} utility for hunting through levels of directories to
+construct a list of file names which you could then pass to @code{tar}.
+@code{find} allows you to be more selective when choosing which files to
+archive; see @ref{files} for more information on using @code{find} with
+@code{tar}, or look.
+
+@table @kbd
+@item --no-recursion
+Prevents @code{tar} from recursively descending directories.
+@end table
+
+When you use @samp{--no-recursion}, GNU @code{tar} grabs directory entries
+themselves, but does not descend on them recursively. Many people use
+@code{find} for locating files they want to back up, and since
+@code{tar} @emph{usually} recursively descends on directories, they have
+to use the @samp{@w{! -d}} option to @code{find} @FIXME{needs more
+explanation or a cite to another info file} as they usually do not want
+all the files in a directory. They then use the @value{op-file-from}
+option to archive the files located via @code{find}.
+
+The problem when restoring files archived in this manner is that the
+directories themselves are not in the archive; so the
+@value{op-same-permissions} option does not affect them---while users
+might really like it to. Specifying @value{op-no-recursion} is a way to
+tell @code{tar} to grab only the directory entries given to it, adding
+no new files on its own.
+
+@FIXME{example here}
+
+@node one, , recurse, Choosing
+@section Crossing Filesystem Boundaries
+@cindex File system boundaries, not crossing
+@UNREVISED
+
+@code{tar} will normally automatically cross file system boundaries in
+order to archive files which are part of a directory tree. You can
+change this behavior by running @code{tar} and specifying
+@value{op-one-file-system}. This option only affects files that are
+archived because they are in a directory that is being archived;
+@code{tar} will still archive files explicitly named on the command line
+or through @value{op-files-from}, regardless of where they reside.
+
+@table @kbd
+@item --one-file-system
+@itemx -l
+Prevents @code{tar} from crossing file system boundaries when
+archiving. Use in conjunction with any write operation.
+@end table
+
+The @samp{--one-file-system} option causes @code{tar} to modify its
+normal behavior in archiving the contents of directories. If a file in
+a directory is not on the same filesystem as the directory itself, then
+@code{tar} will not archive that file. If the file is a directory
+itself, @code{tar} will not archive anything beneath it; in other words,
+@code{tar} will not cross mount points.
+
+It is reported that using this option, the mount point is is archived,
+but nothing under it.
+
+This option is useful for making full or incremental archival backups of
+a file system. If this option is used in conjunction with
+@value{op-verbose}, files that are excluded are mentioned by name on the
+standard error.
+
+@menu
+* directory:: Changing Directory
+* absolute:: Absolute File Names
+@end menu
+
+@node directory, absolute, one, one
+@subsection Changing the Working Directory
+
+@FIXME{need to read over this node now for continuity; i've switched
+things around some.}
+
+@cindex Changing directory mid-stream
+@cindex Directory, changing mid-stream
+@cindex Working directory, specifying
+@UNREVISED
+
+To change the working directory in the middle of a list of file names,
+either on the command line or in a file specified using
+@value{op-files-from}, use @value{op-directory}. This will change the
+working directory to the directory @var{directory} after that point in
+the list.
+
+@table @kbd
+@item --directory=@var{directory}
+@itemx -C @var{directory}
+Changes the working directory in the middle of a command line.
+@end table
+
+For example,
+
+@example
+$ @kbd{tar -c -f jams.tar grape prune -C food cherry}
+@end example
+
+@noindent
+will place the files @file{grape} and @file{prune} from the current
+directory into the archive @file{jams.tar}, followed by the file
+@file{cherry} from the directory @file{food}. This option is especially
+useful when you have several widely separated files that you want to
+store in the same archive.
+
+Note that the file @file{cherry} is recorded in the archive under the
+precise name @file{cherry}, @emph{not} @file{food/cherry}. Thus, the
+archive will contain three files that all appear to have come from the
+same directory; if the archive is extracted with plain @samp{tar
+--extract}, all three files will be written in the current directory.
+
+Contrast this with the command,
+
+@example
+$ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
+@end example
+
+@noindent
+which records the third file in the archive under the name
+@file{red/cherry} so that, if the archive is extracted using
+@samp{tar --extract}, the third file will be written in a subdirectory
+named @file{orange-colored}.
+
+You can use the @samp{--directory} option to make the archive
+independent of the original name of the directory holding the files.
+The following command places the files @file{/etc/passwd},
+@file{/etc/hosts}, and @file{/lib/libc.a} into the archive
+@file{foo.tar}:
+
+@example
+$ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
+@end example
+
+@noindent
+However, the names of the archive members will be exactly what they were
+on the command line: @file{passwd}, @file{hosts}, and @file{libc.a}.
+They will not appear to be related by file name to the original
+directories where those files were located.
+
+Note that @samp{--directory} options are interpreted consecutively. If
+@samp{--directory} specifies a relative file name, it is interpreted
+relative to the then current directory, which might not be the same as
+the original current working directory of @code{tar}, due to a previous
+@samp{--directory} option.
+
+@FIXME{dan: does this mean that you *can* use the short option form, but
+you can *not* use the long option form with --files-from? or is this
+totally screwed?}
+
+When using @samp{--files-from} (@pxref{files}), you can put @samp{-C}
+options in the file list. Unfortunately, you cannot put
+@samp{--directory} options in the file list. (This interpretation can
+be disabled by using the @value{op-null} option.)
+
+@node absolute, , directory, one
+@subsection Absolute File Names
+@UNREVISED
+
+@table @kbd
+@item -P
+@itemx --absolute-names
+Do not strip leading slashes from file names.
+@end table
+
+By default, GNU @code{tar} drops a leading @samp{/} on input or output.
+This option turns off this behavior; it is equivalent to changing to the
+root directory before running @code{tar} (except it also turns off the
+usual warning message).
+
+When @code{tar} extracts archive members from an archive, it strips any
+leading slashes (@samp{/}) from the member name. This causes absolute
+member names in the archive to be treated as relative file names. This
+allows you to have such members extracted wherever you want, instead of
+being restricted to extracting the member in the exact directory named
+in the archive. For example, if the archive member has the name
+@file{/etc/passwd}, @code{tar} will extract it as if the name were
+really @file{etc/passwd}.
+
+Other @code{tar} programs do not do this. As a result, if you create an
+archive whose member names start with a slash, they will be difficult
+for other people with a non-GNU @code{tar} program to use. Therefore,
+GNU @code{tar} also strips leading slashes from member names when
+putting members into the archive. For example, if you ask @code{tar} to
+add the file @file{/bin/ls} to an archive, it will do so, but the member
+name will be @file{bin/ls}.
+
+If you use the @value{op-absolute-names} option, @code{tar} will do
+neither of these transformations.
+
+To archive or extract files relative to the root directory, specify
+the @value{op-absolute-names} option.
+
+Normally, @code{tar} acts on files relative to the working
+directory---ignoring superior directory names when archiving, and
+ignoring leading slashes when extracting.
+
+When you specify @value{op-absolute-names}, @code{tar} stores file names
+including all superior directory names, and preserves leading slashes.
+If you only invoked @code{tar} from the root directory you would never
+need the @value{op-absolute-names} option, but using this option may be
+more convenient than switching to root.
+
+@FIXME{Should be an example in the tutorial/wizardry section using this
+to transfer files between systems.}
+
+@FIXME{Is write access an issue?}
+
+@table @kbd
+@item --absolute-names
+Preserves full file names (inclusing superior dirctory names) when
+archiving files. Preserves leading slash when extracting files.
+
+@end table
+
+@FIXME{this is still horrible; need to talk with dan on monday.}
+
+@code{tar} prints out a message about removing the @samp{/} from file
+names. This message appears once per GNU @code{tar} invocation. It
+represents something which ought to be told; ignoring what it means can
+cause very serious surprises, later.
+
+Some people, nevertheless, do not want to see this message. Wanting to
+play really dangerously, one may of course redirect @code{tar} standard
+error to the sink. For example, under @code{sh}:
+
+@example
+$ @kbd{tar -c -f archive.tar /home 2> /dev/null}
+@end example
+
+@noindent
+Another solution, both nicer and simpler, would be to change to
+the @file{/} directory first, and then avoid absolute notation.
+For example:
+
+@example
+$ @kbd{(cd / && tar -c -f archive.tar home)}
+$ @kbd{tar -c -f archive.tar -C / home}
+@end example
+
+@node Date input formats, Formats, Choosing, Top
+@chapter Date input formats
+
+@cindex date input formats
+@findex getdate
+
+@quotation
+Our units of temporal measurement, from seconds on up to months, are so
+complicated, asymmetrical and disjunctive so as to make coherent mental
+reckoning in time all but impossible. Indeed, had some tyrannical god
+contrived to enslave our minds to time, to make it all but impossible
+for us to escape subjection to sodden routines and unpleasant surprises,
+he could hardly have done better than handing down our present system.
+It is like a set of trapezoidal building blocks, with no vertical or
+horizontal surfaces, like a language in which the simplest thought
+demands ornate constructions, useless particles and lengthy
+circumlocutions. Unlike the more successful patterns of language and
+science, which enable us to face experience boldly or at least
+level-headedly, our system of temporal calculation silently and
+persistently encourages our terror of time.
+
+@dots{} It is as though architects had to measure length in feet, width
+in meters and height in ells; as though basic instruction manuals
+demanded a knowledge of five different languages. It is no wonder then
+that we often look into our own immediate past or future, last Tuesday
+or a week from Sunday, with feelings of helpless confusion. @dots{}
+
+--- Robert Grudin, @cite{Time and the Art of Living}.
+@end quotation
+
+This section describes the textual date representations that GNU
+programs accept. These are the strings you, as a user, can supply as
+arguments to the various programs. The C interface (via the
+@code{getdate} function) is not described here.
+
+@cindex beginning of time, for Unix
+@cindex epoch, for Unix
+Although the date syntax here can represent any possible time since zero
+A.D., computer integers are not big enough for such a (comparatively)
+long time. The earliest date semantically allowed on Unix systems is
+midnight, 1 January 1970 UCT.
+
+@menu
+* General date syntax:: Common rules.
+* Calendar date item:: 19 Dec 1994.
+* Time of day item:: 9:20pm.
+* Timezone item:: EST, DST, BST, UCT, AHST, ...
+* Day of week item:: Monday and others.
+* Relative item in date strings:: next tuesday, 2 years ago.
+* Pure numbers in date strings:: 19931219, 1440.
+* Authors of getdate:: Bellovin, Salz, Berets, et al.
+@end menu
+
+
+@node General date syntax, Calendar date item, Date input formats, Date input formats
+@section General date syntax
+
+@cindex general date syntax
+
+@cindex items in date strings
+A @dfn{date} is a string, possibly empty, containing many items
+separated by whitespace. The whitespace may be omitted when no
+ambiguity arises. The empty string means the beginning of today (i.e.,
+midnight). Order of the items is immaterial. A date string may contain
+many flavors of items:
+
+@itemize @bullet
+@item calendar date items
+@item time of the day items
+@item time zone items
+@item day of the week items
+@item relative items
+@item pure numbers.
+@end itemize
+
+@noindent We describe each of these item types in turn, below.
+
+@cindex numbers, written-out
+@cindex ordinal numbers
+@findex first @r{in date strings}
+@findex next @r{in date strings}
+@findex last @r{in date strings}
+A few numbers may be written out in words in most contexts. This is
+most useful for specifying day of the week items or relative items (see
+below). Here is the list: @samp{first} for 1, @samp{next} for 2,
+@samp{third} for 3, @samp{fourth} for 4, @samp{fifth} for 5,
+@samp{sixth} for 6, @samp{seventh} for 7, @samp{eighth} for 8,
+@samp{ninth} for 9, @samp{tenth} for 10, @samp{eleventh} for 11 and
+@samp{twelfth} for 12. Also, @samp{last} means exactly @math{-1}.
+
+@cindex months, written-out
+When a month is written this way, it is still considered to be written
+numerically, instead of being ``spelled in full''; this changes the
+allowed strings.
+
+@cindex case, ignored in dates
+@cindex comments, in dates
+Alphabetic case is completely ignored in dates. Comments may be introduced
+between round parentheses, as long as included parentheses are properly
+nested. Hyphens not followed by a digit are currently ignored. Leading
+zeros on numbers are ignored.
+
+
+@node Calendar date item, Time of day item, General date syntax, Date input formats
+@section Calendar date item
+
+@cindex calendar date item
+
+A @dfn{calendar date item} specifies a day of the year. It is
+specified differently, depending on whether the month is specified
+numerically or literally. All these strings specify the same calendar date:
+
+@example
+1970-09-17 # ISO 8601.
+70-9-17 # This century assumed by default.
+70-09-17 # Leading zeros are ignored.
+9/17/72 # Common U.S. writing.
+24 September 1972
+24 Sept 72 # September has a special abbreviation.
+24 Sep 72 # Three-letter abbreviations always allowed.
+Sep 24, 1972
+24-sep-72
+24sep72
+@end example
+
+The year can also be omitted. In this case, the last specified year is
+used, or the current year if none. For example:
+
+@example
+9/17
+sep 17
+@end example
+
+Here are the rules.
+
+@cindex ISO 8601 date format
+@cindex date format, ISO 8601
+For numeric months, the ISO 8601 format
+@samp{@var{year}-@var{month}-@var{day}} is allowed, where @var{year} is
+any positive number, @var{month} is a number between 01 and 12, and
+@var{day} is a number between 01 and 31. A leading zero must be present
+if a number is less than ten. If @var{year} is less than 100, then 1900
+is added to it to force a date in this century. The construct
+@samp{@var{month}/@var{day}/@var{year}}, popular in the United States,
+is accepted. Also @samp{@var{month}/@var{day}}, omitting the year.
+
+@cindex month names in date strings
+@cindex abbreviations for months
+Literal months may be spelled out in full: @samp{January},
+@samp{February}, @samp{March}, @samp{April}, @samp{May}, @samp{June},
+@samp{July}, @samp{August}, @samp{September}, @samp{October},
+@samp{November} or @samp{December}. Literal months may be abbreviated
+to their first three letters, possibly followed by an abbreviating dot.
+It is also permitted to write @samp{Sept} instead of @samp{September}.
+
+When months are written literally, the calendar date may be given as any
+of the following:
+
+@example
+@var{day} @var{month} @var{year}
+@var{day} @var{month}
+@var{month} @var{day} @var{year}
+@var{day}-@var{month}-@var{year}
+@end example
+
+Or, omitting the year:
+
+@example
+@var{month} @var{day}
+@end example
+
+
+@node Time of day item, Timezone item, Calendar date item, Date input formats
+@section Time of day item
+
+@cindex time of day item
+
+A @dfn{time of day item} in date strings specifies the time on a given
+day. Here are some examples, all of which represent the same time:
+
+@example
+20:02:0
+20:02
+8:02pm
+20:02-0500 # In EST (Eastern U.S. Standard Time).
+@end example
+
+More generally, the time of the day may be given as
+@samp{@var{hour}:@var{minute}:@var{second}}, where @var{hour} is
+a number between 0 and 23, @var{minute} is a number between 0 and
+59, and @var{second} is a number between 0 and 59. Alternatively,
+@samp{:@var{second}} can be omitted, in which case it is taken to
+be zero.
+
+@findex am @r{in date strings}
+@findex pm @r{in date strings}
+@findex midnight @r{in date strings}
+@findex noon @r{in date strings}
+If the time is followed by @samp{am} or @samp{pm} (or @samp{a.m.}
+or @samp{p.m.}), @var{hour} is restricted to run from 1 to 12, and
+@samp{:@var{minute}} may be omitted (taken to be zero). @samp{am}
+indicates the first half of the day, @samp{pm} indicates the second
+half of the day. In this notation, 12 is the predecessor of 1:
+midnight is @samp{12am} while noon is @samp{12pm}.
+(This is the zero-oriented interpretation of @samp{12am} and @samp{12pm},
+as opposed to the old tradition derived from Latin
+which uses @samp{12m} for noon and @samp{12pm} for midnight.)
+
+@cindex timezone correction
+@cindex minutes, timezone correction by
+The time may alternatively be followed by a timezone correction,
+expressed as @samp{@var{s}@var{hh}@var{mm}}, where @var{s} is @samp{+}
+or @samp{-}, @var{hh} is a number of zone hours and @var{mm} is a number
+of zone minutes. When a timezone correction is given this way, it
+forces interpretation of the time in UTC, overriding any previous
+specification for the timezone or the local timezone. The @var{minute}
+part of the time of the day may not be elided when a timezone correction
+is used. This is the only way to specify a timezone correction by
+fractional parts of an hour.
+
+Either @samp{am}/@samp{pm} or a timezone correction may be specified,
+but not both.
+
+
+@node Timezone item, Day of week item, Time of day item, Date input formats
+@section Timezone item
+
+@cindex timezone item
+
+A @dfn{timezone item} specifies an international timezone, indicated by
+a small set of letters. Any included period is ignored. Military
+timezone designations use a single letter. Currently, only integral
+zone hours may be represented in a timezone item. See the previous
+section for a finer control over the timezone correction.
+
+Here are many non-daylight-savings-time timezones, indexed by the zone
+hour value.
+
+@table @asis
+@item +000
+@cindex Greenwich Mean Time
+@cindex Universal Coordinated Time
+@cindex Western European Time
+@samp{GMT} for Greenwich Mean, @samp{UT} or @samp{UTC} for Universal
+(Coordinated), @samp{WET} for Western European and @samp{Z} for
+militaries.
+@item +100
+@cindex West African Time
+@samp{WAT} for West Africa and
+@samp{A} for militaries.
+@item +200
+@cindex Azores Time
+@samp{AT} for Azores and @samp{B} for militaries.
+@item +300
+@samp{C} for militaries.
+@item +400
+@cindex Atlantic Standard Time
+@samp{AST} for Atlantic Standard and @samp{D} for militaries.
+@item +500
+@cindex Eastern Standard Time
+@samp{E} for militaries and @samp{EST} for Eastern Standard.
+@item +600
+@cindex Central Standard Time
+@samp{CST} for Central Standard and @samp{F} for militaries.
+@item +700
+@cindex Mountain Standard Time
+@samp{G} for militaries and @samp{MST} for Mountain Standard.
+@item +800
+@cindex Pacific Standard Time
+@samp{H} for militaries and @samp{PST} for Pacific Standard.
+@item +900
+@cindex Yukon Standard Time
+@samp{I} for militaries and @samp{YST} for Yukon Standard.
+@item +1000
+@cindex Alaska-Hawaii Time
+@cindex Central Alaska Time
+@cindex Hawaii Standard Time
+@samp{AHST} for Alaska-Hawaii Standard, @samp{CAT} for Central Alaska,
+@samp{HST} for Hawaii Standard and @samp{K} for militaries.
+@item +1100
+@cindex Nome Standard Time
+@samp{L} for militaries and @samp{NT} for Nome.
+@item +1200
+@cindex International Date Line West
+@samp{IDLW} for International Date Line West and @samp{M} for
+militaries.
+@item -100
+@cindex Central European Time
+@cindex Middle European Time
+@cindex Middle European Winter Time
+@cindex French Winter Time
+@cindex Swedish Winter Time
+@samp{CET} for Central European, @samp{FWT} for French Winter,
+@samp{MET} for Middle European, @samp{MEWT} for Middle European
+Winter, @samp{N} for militaries and @samp{SWT} for Swedish Winter.
+@item -200
+@cindex Eastern European Time
+@cindex USSR Zone
+@samp{EET} for Eastern European, USSR Zone 1 and @samp{O} for militaries.
+@item -300
+@cindex Baghdad Time
+@samp{BT} for Baghdad, USSR Zone 2 and @samp{P} for militaries.
+@item -400
+@samp{Q} for militaries and @samp{ZP4} for USSR Zone 3.
+@item -500
+@samp{R} for militaries and @samp{ZP5} for USSR Zone 4.
+@item -600
+@samp{S} for militaries and @samp{ZP6} for USSR Zone 5.
+@item -700
+@cindex West Australian Standard Time
+@samp{T} for militaries and @samp{WAST} for West Australian Standard.
+@item -800
+@cindex China Coast Time
+@samp{CCT} for China Coast, USSR Zone 7 and @samp{U} for militaries.
+@item -900
+@cindex Japan Standard Time
+@samp{JST} for Japan Standard, USSR Zone 8 and @samp{V} for militaries.
+@item -1000
+@cindex East Australian Standard Time
+@cindex Guam Standard Time
+@samp{EAST} for East Australian Standard, @samp{GST} for Guam
+Standard, USSR Zone 9 and @samp{W} for militaries.
+@item -1100
+@samp{X} for militaries.
+@item -1200
+@cindex International Date Line East
+@cindex New Zealand Standard Time
+@samp{IDLE} for International Date Line East, @samp{NZST} for
+New Zealand Standard, @samp{NZT} for New Zealand and @samp{Y} for
+militaries.
+@end table
+
+@cindex daylight savings time
+Here are many DST timezones, indexed by the zone hour value. Also, by
+following a non-DST timezone by the string @samp{DST} in a separate word
+(that is, separated by some whitespace), the corresponding DST timezone
+may be specified.
+
+@table @asis
+@item 0
+@samp{BST} for British Summer.
+@item +400
+@samp{ADT} for Atlantic Daylight.
+@item +500
+@samp{EDT} for Eastern Daylight.
+@item +600
+@samp{CDT} for Central Daylight.
+@item +700
+@samp{MDT} for Mountain Daylight.
+@item +800
+@samp{PDT} for Pacific Daylight.
+@item +900
+@samp{YDT} for Yukon Daylight.
+@item +1000
+@samp{HDT} for Hawaii Daylight.
+@item -100
+@samp{MEST} for Middle European Summer, @samp{MESZ} for Middle European
+Summer, @samp{SST} for Swedish Summer and @samp{FST} for French Summer.
+@item -700
+@samp{WADT} for West Australian Daylight.
+@item -1000
+@samp{EADT} for Eastern Australian Daylight.
+@item -1200
+@samp{NZDT} for New Zealand Daylight.
+@end table
+
+
+@node Day of week item, Relative item in date strings, Timezone item, Date input formats
+@section Day of week item
+
+@cindex day of week item
+
+The explicit mention of a day of the week will forward the date
+(only if necessary) to reach that day of the week in the future.
+
+Days of the week may be spelled out in full: @samp{Sunday},
+@samp{Monday}, @samp{Tuesday}, @samp{Wednesday}, @samp{Thursday},
+@samp{Friday} or @samp{Saturday}. Days may be abbreviated to their
+first three letters, optionally followed by a period. The special
+abbreviations @samp{Tues} for @samp{Tuesday}, @samp{Wednes} for
+@samp{Wednesday} and @samp{Thur} or @samp{Thurs} for @samp{Thursday} are
+also allowed.
+
+@findex next @var{day}
+@findex last @var{day}
+A number may precede a day of the week item to move forward
+supplementary weeks. It is best used in expression like @samp{third
+monday}. In this context, @samp{last @var{day}} or @samp{next
+@var{day}} is also acceptable; they move one week before or after
+the day that @var{day} by itself would represent.
+
+A comma following a day of the week item is ignored.
+
+
+@node Relative item in date strings, Pure numbers in date strings, Day of week item, Date input formats
+@section Relative item in date strings
+
+@cindex relative items in date strings
+@cindex displacement of dates
+
+@dfn{Relative items} adjust a date (or the current date if none) forward
+or backward. The effects of relative items accumulate. Here are some
+examples:
+
+@example
+1 year
+1 year ago
+3 years
+2 days
+@end example
+
+@findex year @r{in date strings}
+@findex month @r{in date strings}
+@findex fortnight @r{in date strings}
+@findex week @r{in date strings}
+@findex day @r{in date strings}
+@findex hour @r{in date strings}
+@findex minute @r{in date strings}
+The unit of time displacement may be selected by the string @samp{year}
+or @samp{month} for moving by whole years or months. These are fuzzy
+units, as years and months are not all of equal duration. More precise
+units are @samp{fortnight} which is worth 14 days, @samp{week} worth 7
+days, @samp{day} worth 24 hours, @samp{hour} worth 60 minutes,
+@samp{minute} or @samp{min} worth 60 seconds, and @samp{second} or
+@samp{sec} worth one second. An @samp{s} suffix on these units is
+accepted and ignored.
+
+@findex ago @r{in date strings}
+The unit of time may be preceded by a multiplier, given as an optionally
+signed number. Unsigned numbers are taken as positively signed. No
+number at all implies 1 for a multiplier. Following a relative item by
+the string @samp{ago} is equivalent to preceding the unit by a
+multiplicator with value @math{-1}.
+
+@findex day @r{in date strings}
+@findex tomorrow @r{in date strings}
+@findex yesterday @r{in date strings}
+The string @samp{tomorrow} is worth one day in the future (equivalent
+to @samp{day}), the string @samp{yesterday} is worth
+one day in the past (equivalent to @samp{day ago}).
+
+@findex now @r{in date strings}
+@findex today @r{in date strings}
+@findex this @r{in date strings}
+The strings @samp{now} or @samp{today} are relative items corresponding
+to zero-valued time displacement, these strings come from the fact
+a zero-valued time displacement represents the current time when not
+otherwise change by previous items. They may be used to stress other
+items, like in @samp{12:00 today}. The string @samp{this} also has
+the meaning of a zero-valued time displacement, but is preferred in
+date strings like @samp{this thursday}.
+
+When a relative item makes the resulting date to cross the boundary
+between DST and non-DST (or vice-versa), the hour is adjusted according
+to the local time.
+
+
+@node Pure numbers in date strings, Authors of getdate, Relative item in date strings, Date input formats
+@section Pure numbers in date strings
+
+@cindex pure numbers in date strings
+
+The precise intepretation of a pure decimal number is dependent of
+the context in the date string.
+
+If the decimal number is of the form @var{yyyy}@var{mm}@var{dd} and no
+other calendar date item (@pxref{Calendar date item}) appears before it
+in the date string, then @var{yyyy} is read as the year, @var{mm} as the
+month number and @var{dd} as the day of the month, for the specified
+calendar date.
+
+If the decimal number is of the form @var{hh}@var{mm} and no other time
+of day item appears before it in the date string, then @var{hh} is read
+as the hour of the day and @var{mm} as the minute of the hour, for the
+specified time of the day. @var{mm} can also be omitted.
+
+If both a calendar date and a time of day appear to the left of a number
+in the date string, but no relative item, then the number overrides the
+year.
+
+
+@node Authors of getdate, , Pure numbers in date strings, Date input formats
+@section Authors of @code{getdate}
+
+@cindex authors of @code{getdate}
+
+@cindex Bellovin, Steven M.
+@cindex Salz, Rich
+@cindex Berets, Jim
+@cindex MacKenzie, David
+@cindex Meyering, Jim
+@code{getdate} was originally implemented by Steven M. Bellovin
+(@samp{smb@@research.att.com}) while at the University of North Carolina
+at Chapel Hill. The code was later tweaked by a couple of people on
+Usenet, then completely overhauled by Rich $alz (@samp{rsalz@@bbn.com})
+and Jim Berets (@samp{jberets@@bbn.com}) in August, 1990. Various
+revisions for the GNU system were made by David MacKenzie, Jim Meyering,
+and others.
+
+@cindex Pinard, F.
+@cindex Berry, K.
+This chapter was originally produced by Fran@,{c}ois Pinard
+(@samp{pinard@@iro.umontreal.ca}) from the @file{getdate.y} source code,
+and then edited by K.@: Berry (@samp{kb@@cs.umb.edu}).
+
+@node Formats, Media, Date input formats, Top
+@chapter Controlling the Archive Format
+
+@FIXME{need an intro here}
+
+@menu
+* Portability:: Making @code{tar} Archives More Portable
+* Compression:: Using Less Space through Compression
+* Attributes:: Handling File Attributes
+* Standard:: The Standard Format
+* Extensions:: GNU Extensions to the Archive Format
+* cpio:: Comparison of @code{tar} and @code{cpio}
+@end menu
+
+@node Portability, Compression, Formats, Formats
+@section Making @code{tar} Archives More Portable
+
+Creating a @code{tar} archive on a particular system that is meant to be
+useful later on many other machines and with other versions of @code{tar}
+is more challenging than you might think. @code{tar} archive formats
+have been evolving since the first versions of Unix. Many such formats
+are around, and are not always comptible with each other. This section
+discusses a few problems, and gives some advice about making @code{tar}
+archives more portable.
+
+One golden rule is simplicity. For example, limit your @code{tar}
+archives to contain only regular files and directories, avoiding
+other kind of special files. Do not attempt to save sparse files or
+contiguous files as such. Let's discuss a few more problems, in turn.
+
+@menu
+* Portable Names:: Portable Names
+* dereference:: Symbolic Links
+* old:: Old V7 Archives
+* posix:: POSIX archives
+* Checksumming:: Checksumming Problems
+@end menu
+
+@node Portable Names, dereference, Portability, Portability
+@subsection Portable Names
+
+Use @emph{straight} file and directory names, made up of printable
+ASCII characters, avoiding colons, slashes, backslashes, spaces, and
+other @emph{dangerous} characters. Avoid deep directory nesting.
+Accounting for oldish System V machines, limit your file and directory
+names to 14 characters or less.
+
+If you intend to have your @code{tar} archives to be read under MSDOS,
+you should not rely on case distinction for file names, and you might
+use the GNU @code{doschk} program for helping you further diagnosing
+illegal MSDOS names, which are even more limited than System V's.
+
+@node dereference, old, Portable Names, Portability
+@subsection Symbolic Links
+@cindex File names, using symbolic links
+@cindex Symbolic link as file name
+
+Normally, when @code{tar} archives a symbolic link, it writes a
+block to the archive naming the target of the link. In that way, the
+@code{tar} archive is a faithful record of the filesystem contents.
+@value{op-dereference} is used with @value{op-create}, and causes @code{tar}
+to archive the files symbolic links point to, instead of the links
+themselves. When this option is used, when @code{tar} encounters a
+symbolic link, it will archive the linked-to file, instead of simply
+recording the presence of a symbolic link.
+
+The name under which the file is stored in the file system is not
+recorded in the archive. To record both the symbolic link name and
+the file name in the system, archive the file under both names. If
+all links were recorded automatically by @code{tar}, an extracted file
+might be linked to a file name that no longer exists in the file
+system.
+
+If a linked-to file is encountered again by @code{tar} while creating
+the same archive, an entire second copy of it will be stored. (This
+@emph{might} be considered a bug.)
+
+So, for portable archives, do not archive symbolic links as such,
+and use @value{op-dereference}: many systems do not support
+symbolic links, and moreover, your distribution might be unusable if
+it contains unresolved symbolic links.
+
+@node old, posix, dereference, Portability
+@subsection Old V7 Archives
+@cindex Format, old style
+@cindex Old style format
+@cindex Old style archives
+
+Certain old versions of @code{tar} cannot handle additional
+information recorded by newer @code{tar} programs. To create an
+archive in V7 format (not ANSI), which can be read by these old
+versions, specify the @value{op-old-archive} option in
+conjunction with the @value{op-create}. @code{tar} also
+accepts @samp{--portability} for this option. When you specify it,
+@code{tar} leaves out information about directories, pipes, fifos,
+contiguous files, and device files, and specifies file ownership by
+group and user IDs instead of group and user names.
+
+When updating an archive, do not use @value{op-old-archive}
+unless the archive was created with using this option.
+
+In most cases, a @emph{new} format archive can be read by an @emph{old}
+@code{tar} program without serious trouble, so this option should
+seldom be needed. On the other hand, most modern @code{tar}s are
+able to read old format archives, so it might be safer for you to
+always use @value{op-old-archive} for your distributions.
+
+@node posix, Checksumming, old, Portability
+@subsection GNU @code{tar} and POSIX @code{tar}
+
+GNU @code{tar} was based on an early draft of the POSIX 1003.1
+@code{ustar} standard. GNU extensions to @code{tar}, such as the
+support for file names longer than 100 characters, use portions of the
+@code{tar} header record which were specified in that POSIX draft as
+unused. Subsequent changes in POSIX have allocated the same parts of
+the header record for other purposes. As a result, GNU @code{tar} is
+incompatible with the current POSIX spec, and with @code{tar} programs
+that follow it.
+
+We plan to reimplement these GNU extensions in a new way which is
+upward compatible with the latest POSIX @code{tar} format, but we
+don't know when this will be done.
+
+In the mean time, there is simply no telling what might happen if you
+read a GNU @code{tar} archive, which uses the GNU extensions, using
+some other @code{tar} program. So if you want to read the archive
+with another @code{tar} program, be sure to write it using the
+@samp{--old-archive} option (@samp{-o}).
+
+@FIXME{is there a way to tell which flavor of tar was used to write a
+particular archive before you try to read it?}
+
+Traditionally, old @code{tar}s have a limit of 100 characters. GNU
+@code{tar} attempted two different approaches to overcome this limit,
+using and extending a format specified by a draft of some P1003.1.
+The first way was not that successful, and involved @file{@@MaNgLeD@@}
+file names, or such; while a second approach used @file{././@@LongLink}
+and other tricks, yielding better success. In theory, GNU @code{tar}
+should be able to handle file names of practically unlimited length.
+So, if GNU @code{tar} fails to dump and retrieve files having more
+than 100 characters, then there is a bug in GNU @code{tar}, indeed.
+
+But, being strictly POSIX, the limit was still 100 characters.
+For various other purposes, GNU @code{tar} used areas left unassigned
+in the POSIX draft. POSIX later revised P1003.1 @code{ustar} format by
+assigning previously unused header fields, in such a way that the upper
+limit for file name length was raised to 256 characters. However, the
+actual POSIX limit oscillates between 100 and 256, depending on the
+precise location of slashes in full file name (this is rather ugly).
+Since GNU @code{tar} use the same fields for quite other purposes,
+it became incompatible with the latest POSIX standards.
+
+For longer or non-fitting file names, we plan to use yet another set
+of GNU extensions, but this time, complying with the provisions POSIX
+offers for extending the format, rather than conflicting with it.
+Whenever an archive uses old GNU @code{tar} extension format or POSIX
+extensions, would it be for very long file names or other specialities,
+this archive becomes non-portable to other @code{tar} implementations.
+In fact, anything can happen. The most forgiving @code{tar}s will
+merely unpack the file using a wrong name, and maybe create another
+file named something like @file{@@LongName}, with the true file name
+in it. @code{tar}s not protecting themselves may segment violate!
+
+Compatibility concerns make all this thing more difficult, as we
+will have to support @emph{all} these things together, for a while.
+GNU @code{tar} should be able to produce and read true POSIX format
+files, while being able to detect old GNU @code{tar} formats, besides
+old V7 format, and process them conveniently. It would take years
+before this whole area stabilizes@dots{}
+
+There are plans to raise this 100 limit to 256, and yet produce POSIX
+conformant archives. Past 256, I do not know yet if GNU @code{tar}
+will go non-POSIX again, or merely refuse to archive the file.
+
+There are plans so GNU @code{tar} support more fully the latest POSIX
+format, while being able to read old V7 format, GNU (semi-POSIX plus
+extension), as well as full POSIX. One may ask if there is part of
+the POSIX format that we still cannot support. This simple question
+has a complex answer. Maybe that, on intimate look, some strong
+limitations will pop up, but until now, nothing sounds too difficult
+(but see below). I only have these few pages of POSIX telling about
+`Extended tar Format' (P1003.1-1990 -- section 10.1.1), and there are
+references to other parts of the standard I do not have, which should
+normally enforce limitations on stored file names (I suspect things
+like fixing what @kbd{/} and @kbd{@key{NUL}} means). There are also
+some points which the standard does not make clear, Existing practice
+will then drive what I should do.
+
+POSIX mandates that, when a file name cannot fit within 100 to
+256 characters (the variance comes from the fact a @kbd{/} is
+ideally needed as the 156'th character), or a link name cannot
+fit within 100 characters, a warning should be issued and the file
+@emph{not} be stored. Unless some @value{op-posix} option is given
+(or @code{POSIXLY_CORRECT} is set), I suspect that GNU @code{tar}
+should disobey this specification, and automatically switch to using
+GNU extensions to overcome file name or link name length limitations.
+
+There is a problem, however, which I did not intimately studied yet.
+Given a truly POSIX archive with names having more than 100 characters,
+I guess that GNU @code{tar} up to 1.11.8 will process it as if it were an
+old V7 archive, and be fooled by some fields which are coded differently.
+So, the question is to decide if the next generation of GNU @code{tar}
+should produce POSIX format by default, whenever possible, producing
+archives older versions of GNU @code{tar} might not be able to read
+correctly. I fear that we will have to suffer such a choice one of these
+days, if we want GNU @code{tar} to go closer to POSIX. We can rush it.
+Another possibility is to produce the current GNU @code{tar} format
+by default for a few years, but have GNU @code{tar} versions from some
+1.@var{POSIX} and up able to recognize all three formats, and let older
+GNU @code{tar} fade out slowly. Then, we could switch to producing POSIX
+format by default, with not much harm to those still having (very old at
+that time) GNU @code{tar} versions prior to 1.@var{POSIX}.
+
+POSIX format cannot represent very long names, volume headers,
+splitting of files in multi-volumes, sparse files, and incremental
+dumps; these would be all disallowed if @value{op-posix} or
+@code{POSIXLY_CORRECT}. Otherwise, if @code{tar} is given long
+names, or @samp{-[VMSgG]}, then it should automatically go non-POSIX.
+I think this is easily granted without much discussion.
+
+Another point is that only @code{mtime} is stored in POSIX
+archives, while GNU @code{tar} currently also store @code{atime}
+and @code{ctime}. If we want GNU @code{tar} to go closer to POSIX,
+my choice would be to drop @code{atime} and @code{ctime} support on
+average. On the other hand, I perceive that full dumps or incremental
+dumps need @code{atime} and @code{ctime} support, so for those special
+applications, POSIX has to be avoided altogether.
+
+A few users requested that @value{op-sparse} be always active by
+default, I think that before replying to them, we have to decide
+if we want GNU @code{tar} to go closer to POSIX on average, while
+producing files. My choice would be to go closer to POSIX in the
+long run. Besides possible double reading, I do not see any point
+of not trying to save files as sparse when creating archives which
+are neither POSIX nor old-V7, so the actual @value{op-sparse} would
+become selected by default when producing such archives, whatever
+the reason is. So, @value{op-sparse} alone might be redefined to force
+GNU-format archives, and recover its previous meaning from this fact.
+
+GNU-format as it exists now can easily fool other POSIX @code{tar},
+as it uses fields which POSIX considers to be part of the file name
+prefix. I wonder if it would not be a good idea, in the long run,
+to try changing GNU-format so any added field (like @code{ctime},
+@code{atime}, file offset in subsequent volumes, or sparse file
+descriptions) be wholly and always pushed into an extension block,
+instead of using space in the POSIX header block. I could manage
+to do that portably between future GNU @code{tar}s. So other POSIX
+@code{tar}s might be at least able to provide kind of correct listings
+for the archives produced by GNU @code{tar}, if not able to process
+them otherwise.
+
+Using these projected extensions might induce older @code{tar}s to fail.
+We would use the same approach as for POSIX. I'll put out a @code{tar}
+capable of reading POSIXier, yet extended archives, but will not produce
+this format by default, in GNU mode. In a few years, when newer GNU
+@code{tar}s will have flooded out @code{tar} 1.11.X and previous, we
+could switch to producing POSIXier extended archives, with no real harm
+to users, as almost all existing GNU @code{tar}s will be ready to read
+POSIXier format. In fact, I'll do both changes at the same time, in a
+few years, and just prepare @code{tar} for both changes, without effecting
+them, from 1.@var{POSIX}. (Both changes: 1---using POSIX convention for
+getting over 100 characters; 2---avoiding mangling POSIX headers for GNU
+extensions, using only POSIX mandated extension techniques).
+
+So, a future @code{tar} will have a @value{op-posix}
+flag forcing the usage of truly POSIX headers, and so, producing
+archives previous GNU @code{tar} will not be able to read.
+So, @emph{once} pretest will announce that feature, it would be
+particularly useful that users test how exchangeable will be archives
+between GNU @code{tar} with @value{op-posix} and other POSIX @code{tar}.
+
+In a few years, when GNU @code{tar} will produce POSIX headers by
+default, @value{op-posix} will have a strong meaning and will disallow
+GNU extensions. But in the meantime, for a long while, @value{op-posix}
+in GNU tar will not disallow GNU extensions like @value{op-label},
+@value{op-multi-volume}, @value{op-sparse}, or very long file or link names.
+However, @value{op-posix} with GNU extensions will use POSIX
+headers with reserved-for-users extensions to headers, and I will be
+curious to know how well or bad POSIX @code{tar}s will react to these.
+
+GNU @code{tar} prior to 1.@var{POSIX}, and after 1.@var{POSIX} without
+@value{op-posix}, generates and checks @samp{ustar@w{ }@w{ }}, with two
+suffixed spaces. This is sufficient for older GNU @code{tar} not to
+recognize POSIX archives, and consequently, wrongly decide those archives
+are in old V7 format. It is a useful bug for me, because GNU @code{tar}
+has other POSIX incompatibilities, and I need to segregate GNU @code{tar}
+semi-POSIX archives from truly POSIX archives, for GNU @code{tar} should
+be somewhat compatible with itself, while migrating closer to latest
+POSIX standards. So, I'll be very careful about how and when I will do
+the correction.
+
+@node Checksumming, , posix, Portability
+@subsection Checksumming Problems
+
+SunOS and HP-UX @code{tar} fail to accept archives created using GNU
+@code{tar} and containing non-ASCII file names, that is, file names
+having characters with the eight bit set, because they use signed
+checksums, while GNU @code{tar} uses unsigned checksums while creating
+archives, as per POSIX standards. On reading, GNU @code{tar} computes
+both checksums and accept any. It is somewhat worrying that a lot of
+people may go around doing backup of their files using faulty (or at
+least non-standard) software, not learning about it until it's time
+to restore their missing files with an incompatible file extractor,
+or vice versa.
+
+GNU @code{tar} compute checksums both ways, and accept any on read,
+so GNU tar can read Sun tapes even with their wrong checksums.
+GNU @code{tar} produces the standard checksum, however, raising
+incompatibilities with Sun. That is to say, GNU @code{tar} has not
+been modified to @emph{produce} incorrect archives to be read by buggy
+@code{tar}'s. I've been told that more recent Sun @code{tar} now
+read standard archives, so maybe Sun did a similar patch, after all?
+
+The story seems to be that when Sun first imported @code{tar}
+sources on their system, they recompiled it without realizing that
+the checksums were computed differently, because of a change in
+the default signing of @code{char}'s in their compiler. So they
+started computing checksums wrongly. When they later realized their
+mistake, they merely decided to stay compatible with it, and with
+themselves afterwards. Presumably, but I do not really know, HP-UX
+has chosen that their @code{tar} archives to be compatible with Sun's.
+The current standards do not favor Sun @code{tar} format. In any
+case, it now falls on the shoulders of SunOS and HP-UX users to get
+a @code{tar} able to read the good archives they receive.
+
+@node Compression, Attributes, Portability, Formats
+@section Using Less Space through Compression
+
+@menu
+* gzip:: Creating and Reading Compressed Archives
+* sparse:: Archiving Sparse Files
+@end menu
+
+@node gzip, sparse, Compression, Compression
+@subsection Creating and Reading Compressed Archives
+@cindex Compressed archives
+@cindex Storing archives in compressed format
+@UNREVISED
+
+@table @kbd
+@item -z
+@itemx --gzip
+@itemx --ungzip
+Filter the archive through @code{gzip}.
+@end table
+
+@FIXME{ach; these two bits orig from "compare" (?). where to put?} Some
+format parameters must be taken into consideration when modifying an
+archive: @FIXME{???}. Compressed archives cannot be modified.
+
+You can use @samp{--gzip} and @samp{--gunzip} on physical devices
+(tape drives, etc.) and remote files as well as on normal files; data
+to or from such devices or remote files is reblocked by another copy
+of the @code{tar} program to enforce the specified (or default) record
+size. The default compression parameters are used; if you need to
+override them, avoid the @value{op-gzip} option and run @code{gzip}
+explicitly. (Or set the @samp{GZIP} environment variable.)
+
+The @value{op-gzip} option does not work with the @value{op-multi-volume}
+option, or with the @value{op-update}, @value{op-append},
+@value{op-concatenate}, or @value{op-delete} operations.
+
+It is not exact to say that GNU @code{tar} is to work in concert
+with @code{gzip} in a way similar to @code{zip}, say. Surely, it is
+possible that @code{tar} and @code{gzip} be done with a single call,
+like in:
+
+@example
+$ @kbd{tar cfz archive.tar.gz subdir}
+@end example
+
+@noindent
+to save all of @samp{subdir} into a @code{gzip}'ed archive. Later you
+can do:
+
+@example
+$ @kbd{tar xfz archive.tar.gz}
+@end example
+
+@noindent
+to explode and unpack.
+
+The difference is that the whole archive is compressed. With
+@code{zip}, archive members are archived individually. @code{tar}'s
+method yields better compression. On the other hand, one can view the
+contents of a @code{zip} archive without having to decompress it. As
+for the @code{tar} and @code{gzip} tandem, you need to decompress the
+archive to see its contents. However, this may be done without needing
+disk space, by using pipes internally:
+
+@example
+$ @kbd{tar tfz archive.tar.gz}
+@end example
+
+@cindex corrupted archives
+About corrupted compressed archives: @code{gzip}'ed files have no
+redundancy, for maximum compression. The adaptive nature of the
+compression scheme means that the compression tables are implicitly
+spread all over the archive. If you lose a few blocks, the dynamic
+construction of the compression tables becomes unsychronized, and there
+is little chance that you could recover later in the archive.
+
+There are pending suggestions for having a per-volume or per-file
+compression in GNU @code{tar}. This would allow for viewing the
+contents without decompression, and for resynchronizing decompression at
+every volume or file, in case of corrupted archives. Doing so, we might
+loose some compressibility. But this would have make recovering easier.
+So, there are pros and cons. We'll see!
+
+@table @kbd
+@item -Z
+@itemx --compress
+@itemx --uncompress
+Filter the archive through @code{compress}. Otherwise like @value{op-gzip}.
+
+@item --use-compress-program=@var{prog}
+Filter through @var{prog} (must accept @samp{-d}).
+@end table
+
+@value{op-compress} stores an archive in compressed format. This
+option is useful in saving time over networks and space in pipes, and
+when storage space is at a premium. @value{op-compress} causes
+@code{tar} to compress when writing the archive, or to uncompress when
+reading the archive.
+
+To perform compression and uncompression on the archive, @code{tar}
+runs the @code{compress} utility. @code{tar} uses the default
+compression parameters; if you need to override them, avoid the
+@value{op-compress} option and run the @code{compress} utility
+explicitly. It is useful to be able to call the @code{compress}
+utility from within @code{tar} because the @code{compress} utility by
+itself cannot access remote tape drives.
+
+The @value{op-compress} option will not work in conjunction with the
+@value{op-multi-volume} option or the @value{op-append}, @value{op-update},
+@value{op-append} and @value{op-delete} operations. @xref{Operations}, for
+more information on these operations.
+
+If there is no compress utility available, @code{tar} will report an error.
+@strong{Please note} that the @code{compress} program may be covered by
+a patent, and therefore we recommend you stop using it.
+
+@table @kbd
+@item --compress
+@itemx --uncompress
+@itemx -z
+@itemx -Z
+When this option is specified, @code{tar} will compress (when writing
+an archive), or uncompress (when reading an archive). Used in
+conjunction with the @value{op-create}, @value{op-extract}, @value{op-list} and
+@value{op-compare} operations.
+@end table
+
+You can have archives be compressed by using the @value{op-gzip} option.
+This will arrange for @code{tar} to use the @code{gzip} program to be
+used to compress or uncompress the archive wren writing or reading it.
+
+To use the older, obsolete, @code{compress} program, use the
+@value{op-compress} option. The GNU Project recommends you not use
+@code{compress}, because there is a patent covering the algorithm it
+uses. You could be sued for patent infringment merely by running
+@code{compress}.
+
+I have one question, or maybe it's a suggestion if there isn't a way
+to do it now. I would like to use @value{op-gzip}, but I'd also like the
+output to be fed through a program like GNU @code{ecc} (actually, right
+now that's @samp{exactly} what I'd like to use :-)), basically adding
+ECC protection on top of compression. It seems as if this should be
+quite easy to do, but I can't work out exactly how to go about it.
+Of course, I can pipe the standard output of @code{tar} through
+@code{ecc}, but then I lose (though I haven't started using it yet,
+I confess) the ability to have @code{tar} use @code{rmt} for it's I/O
+(I think).
+
+I think the most straightforward thing would be to let me specify a
+general set of filters outboard of compression (preferably ordered,
+so the order can be automatically reversed on input operations, and
+with the options they require specifiable), but beggars shouldn't be
+choosers and anything you decide on would be fine with me.
+
+By the way, I like @code{ecc} but if (as the comments say) it can't
+deal with loss of block sync, I'm tempted to throw some time at adding
+that capability. Supposing I were to actually do such a thing and
+get it (apparantly) working, do you accept contributed changes to
+utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995).
+
+Isn't that exactly the role of the @value{op-use-compress-prog} option?
+I never tried it myself, but I suspect you may want to write a
+@var{prog} script or program able to filter stdin to stdout to
+way you want. It should recognize the @samp{-d} option, for when
+extraction is needed rather than creation.
+
+It has been reported that if one writes compressed data (through the
+@value{op-gzip} or @value{op-compress} options) to a DLT and tries to use
+the DLT compression mode, the data will actually get bigger and one will
+end up with less space on the tape.
+
+@node sparse, , gzip, Compression
+@subsection Archiving Sparse Files
+@cindex Sparse Files
+@UNREVISED
+
+@table @kbd
+@item -S
+@itemx --sparse
+Handle sparse files efficiently.
+@end table
+
+This option causes all files to be put in the archive to be tested for
+sparseness, and handled specially if they are. The @value{op-sparse}
+option is useful when many @code{dbm} files, for example, are being
+backed up. Using this option dramatically decreases the amount of
+space needed to store such a file.
+
+In later versions, this option may be removed, and the testing and
+treatment of sparse files may be done automatically with any special
+GNU options. For now, it is an option needing to be specified on
+the command line with the creation or updating of an archive.
+
+Files in the filesystem occasionally have ``holes.'' A hole in a file
+is a section of the file's contents which was never written. The
+contents of a hole read as all zeros. On many operating systems,
+actual disk storage is not allocated for holes, but they are counted
+in the length of the file. If you archive such a file, @code{tar}
+could create an archive longer than the original. To have @code{tar}
+attempt to recognize the holes in a file, use @value{op-sparse}. When
+you use the @value{op-sparse} option, then, for any file using less
+disk space than would be expected from its length, @code{tar} searches
+the file for consecutive stretches of zeros. It then records in the
+archive for the file where the consecutive stretches of zeros are, and
+only archives the ``real contents'' of the file. On extraction (using
+@value{op-sparse} is not needed on extraction) any such files have
+hols created wherever the continuous stretches of zeros were found.
+Thus, if you use @value{op-sparse}, @code{tar} archives won't take
+more space than the original.
+
+A file is sparse if it contains blocks of zeros whose existence is
+recorded, but that have no space allocated on disk. When you specify
+the @value{op-sparse} option in conjunction with the @value{op-create}
+operation, @code{tar} tests all files for sparseness while archiving.
+If @code{tar} finds a file to be sparse, it uses a sparse representation of
+the file in the archive. @value{xref-create}, for more information
+about creating archives.
+
+@value{op-sparse} is useful when archiving files, such as dbm files,
+likely to contain many nulls. This option dramatically
+decreases the amount of space needed to store such an archive.
+
+@quotation
+@strong{Please Note:} Always use @value{op-sparse} when performing file
+system backups, to avoid archiving the expanded forms of files stored
+sparsely in the system.
+
+Even if your system has no sparse files currently, some may be
+created in the future. If you use @value{op-sparse} while making file
+system backups as a matter of course, you can be assured the archive
+will never take more space on the media than the files take on disk
+(otherwise, archiving a disk filled with sparse files might take
+hundreds of tapes). @FIXME-xref{incremental when node name is set.}
+@end quotation
+
+@code{tar} ignores the @value{op-sparse} option when reading an archive.
+
+@table @kbd
+@item --sparse
+@itemx -S
+Files stored sparsely in the file system are represented sparsely in
+the archive. Use in conjunction with write operations.
+@end table
+
+However, users should be well aware that at archive creation time, GNU
+@code{tar} still has to read whole disk file to locate the @dfn{holes}, and
+so, even if sparse files use little space on disk and in the archive, they
+may sometimes require inordinate amount of time for reading and examining
+all-zero blocks of a file. Although it works, it's painfully slow for a
+large (sparse) file, even though the resulting tar archive may be small.
+(One user reports that dumping a @file{core} file of over 400 megabytes,
+but with only about 3 megabytes of actual data, took about 9 minutes on
+a Sun Sparstation ELC, with full CPU utilisation.)
+
+This reading is required in all cases and is not related to the fact
+the @value{op-sparse} option is used or not, so by merely @emph{not}
+using the option, you are not saving time@footnote{Well! We should say
+the whole truth, here. When @value{op-sparse} is selected while creating
+an archive, the current @code{tar} algorithm requires sparse files to be
+read twice, not once. We hope to develop a new archive format for saving
+sparse files in which one pass will be sufficient.}.
+
+Programs like @code{dump} do not have to read the entire file; by examining
+the file system directly, they can determine in advance exactly where the
+holes are and thus avoid reading through them. The only data it need read
+are the actual allocated data blocks. GNU @code{tar} uses a more portable
+and straightforward archiving approach, it would be fairly difficult that
+it does otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals},
+on 1990-12-10:
+
+@quotation
+What I did say is that you cannot tell the difference between a hole and an
+equivalent number of nulls without reading raw blocks. @code{st_blocks} at
+best tells you how many holes there are; it doesn't tell you @emph{where}.
+Just as programs may, conceivably, care what @code{st_blocks} is (care
+to name one that does?), they may also care where the holes are (I have
+no examples of this one either, but it's equally imaginable).
+
+I conclude from this that good archivers are not portable. One can
+arguably conclude that if you want a portable program, you can in good
+conscience restore files with as many holes as possible, since you can't
+get it right.
+@end quotation
+
+@node Attributes, Standard, Compression, Formats
+@section Handling File Attributes
+@UNREVISED
+
+When @code{tar} reads files, this causes them to have the access times
+updated. To have @code{tar} attempt to set the access times back to
+what they were before they were read, use the @value{op-atime-preserve}
+option. This doesn't work for files that you don't own, unless
+you're root, and it doesn't interact with incremental dumps nicely
+(@pxref{Backups}), but it is good enough for some purposes.
+
+Handling of file attributes
+
+@table @kbd
+@item --atime-preserve
+Do not change access times on dumped files.
+
+@item -m
+@itemx --touch
+Do not extract file modified time.
+
+When this option is used, @code{tar} leaves the modification times
+of the files it extracts as the time when the files were extracted,
+instead of setting it to the time recorded in the archive.
+
+This option is meaningless with @value{op-list}.
+
+@item --same-owner
+Create extracted files with the same ownership they have in the
+archive.
+
+When using super-user at extraction time, ownership is always restored.
+So, this option is meaningful only for non-root users, when @code{tar}
+is executed on those systems able to give files away. This is
+considered as a security flaw by many people, at least because it
+makes quite difficult to correctly account users for the disk space
+they occupy. Also, the @code{suid} or @code{sgid} attributes of
+files are easily and silently lost when files are given away.
+
+When writing an archive, @code{tar} writes the user id and user name
+separately. If it can't find a user name (because the user id is not
+in @file{/etc/passwd}), then it does not write one. When restoring,
+and doing a @code{chmod} like when you use @value{op-same-permissions}
+(@FIXME{same-owner?}), it tries to look the name (if one was written)
+up in @file{/etc/passwd}. If it fails, then it uses the user id
+stored in the archive instead.
+
+@item --numeric-owner
+The @value{op-numeric-owner} option allows (ANSI) archives to be written
+without user/group name information or such information to be ignored
+when extracting. It effectively disables the generation and/or use
+of user/group name information. This option forces extraction using
+the numeric ids from the archive, ignoring the names.
+
+This is useful in certain circumstances, when restoring a backup from
+an emergency floppy with different passwd/group files for example.
+It is otherwise impossible to extract files with the right ownerships
+if the password file in use during the extraction does not match the
+one belonging to the filesystem(s) being extracted. This occurs,
+for example, if you are restoring your files after a major crash and
+had booted from an emergency floppy with no password file or put your
+disk into another machine to do the restore.
+
+The numeric ids are @emph{always} saved into @code{tar} archives.
+The identifying names are added at create time when provided by the
+system, unless @value{op-old-archive} is used. Numeric ids could be
+used when moving archives between a collection of machines using
+a centralized management for attribution of numeric ids to users
+and groups. This is often made through using the NIS capabilities.
+
+When making a @code{tar} file for distribution to other sites, it
+is sometimes cleaner to use a single owner for all files in the
+distribution, and nicer to specify the write permission bits of the
+files as stored in the archive independently of their actual value on
+the file system. The way to prepare a clean distribution is usually
+to have some Makefile rule creating a directory, copying all needed
+files in that directory, then setting ownership and permissions as
+wanted (there are a lot of possible schemes), and only then making a
+@code{tar} archive out of this directory, before cleaning everything
+out. Of course, we could add a lot of options to GNU @code{tar} for
+fine tuning permissions and ownership. This is not the good way,
+I think. GNU @code{tar} is already crowded with options and moreover,
+the approach just explained gives you a great deal of control already.
+
+@item -p
+@itemx --same-permissions
+@itemx --preserve-permissions
+Extract all protection information.
+
+This option causes @code{tar} to set the modes (access permissions) of
+extracted files exactly as recorded in the archive. If this option
+is not used, the current @code{umask} setting limits the permissions
+on extracted files.
+
+This option is meaningless with @value{op-list}.
+
+@item --preserve
+Same as both @value{op-same-permissions} and @value{op-same-order}.
+
+The @value{op-preserve} option has no equivalent short option name.
+It is equivalent to @value{op-same-permissions} plus @value{op-same-order}.
+
+@FIXME{I do not see the purpose of such an option. (Neither I. FP.)}
+
+@end table
+
+@node Standard, Extensions, Attributes, Formats
+@section The Standard Format
+@UNREVISED
+
+While an archive may contain many files, the archive itself is a
+single ordinary file. Like any other file, an archive file can be
+written to a storage device such as a tape or disk, sent through a
+pipe or over a network, saved on the active file system, or even
+stored in another archive. An archive file is not easy to read or
+manipulate without using the @code{tar} utility or Tar mode in GNU
+Emacs.
+
+Physically, an archive consists of a series of file entries terminated
+by an end-of-archive entry, which consists of 512 zero bytes. A file
+entry usually describes one of the files in the archive (an
+@dfn{archive member}), and consists of a file header and the contents
+of the file. File headers contain file names and statistics, checksum
+information which @code{tar} uses to detect file corruption, and
+information about file types.
+
+Archives are permitted to have more than one member with the same
+member name. One way this situation can occur is if more than one
+version of a file has been stored in the archive. For information
+about adding new versions of a file to an archive, see @ref{update},
+and to learn more about having more than one archive member with the
+same name, see @FIXME-xref{-backup node, when it's written}.
+
+In addition to entries describing archive members, an archive may
+contain entries which @code{tar} itself uses to store information.
+@value{xref-label}, for an example of such an archive entry.
+
+A @code{tar} archive file contains a series of blocks. Each block
+contains @code{BLOCKSIZE} bytes. Although this format may be thought
+of as being on magnetic tape, other media are often used.
+
+Each file archived is represented by a header block which describes
+the file, followed by zero or more blocks which give the contents
+of the file. At the end of the archive file there may be a block
+filled with binary zeros as an end-of-file marker. A reasonable system
+should write a block of zeros at the end, but must not assume that
+such a block exists when reading an archive.
+
+The blocks may be @dfn{blocked} for physical I/O operations.
+Each record of @var{n} blocks (where @var{n} is set by the
+@value{op-blocking-factor} option to @code{tar}) is written with a single
+@w{@samp{write ()}} operation. On magnetic tapes, the result of
+such a write is a single record. When writing an archive,
+the last record of blocks should be written at the full size, with
+blocks after the zero block containing all zeros. When reading
+an archive, a reasonable system should properly handle an archive
+whose last record is shorter than the rest, or which contains garbage
+records after a zero block.
+
+The header block is defined in C as follows. In the GNU @code{tar}
+distribution, this is part of file @file{src/tar.h}:
+
+@example
+@include header.texi
+@end example
+
+All characters in header blocks are represented by using 8-bit
+characters in the local variant of ASCII. Each field within the
+structure is contiguous; that is, there is no padding used within
+the structure. Each character on the archive medium is stored
+contiguously.
+
+Bytes representing the contents of files (after the header block
+of each file) are not translated in any way and are not constrained
+to represent characters in any character set. The @code{tar} format
+does not distinguish text files from binary files, and no translation
+of file contents is performed.
+
+The @code{name}, @code{linkname}, @code{magic}, @code{uname}, and
+@code{gname} are null-terminated character strings. All other fileds
+are zero-filled octal numbers in ASCII. Each numeric field of width
+@var{w} contains @var{w} minus 2 digits, a space, and a null, except
+@code{size}, and @code{mtime}, which do not contain the trailing null.
+
+The @code{name} field is the file name of the file, with directory names
+(if any) preceding the file name, separated by slashes.
+
+@FIXME{how big a name before field overflows?}
+
+The @code{mode} field provides nine bits specifying file permissions
+and three bits to specify the Set UID, Set GID, and Save Text
+(@dfn{sticky}) modes. Values for these bits are defined above.
+When special permissions are required to create a file with a given
+mode, and the user restoring files from the archive does not hold such
+permissions, the mode bit(s) specifying those special permissions
+are ignored. Modes which are not supported by the operating system
+restoring files from the archive will be ignored. Unsupported modes
+should be faked up when creating or updating an archive; e.g. the
+group permission could be copied from the @emph{other} permission.
+
+The @code{uid} and @code{gid} fields are the numeric user and group
+ID of the file owners, respectively. If the operating system does
+not support numeric user or group IDs, these fields should be ignored.
+
+The @code{size} field is the size of the file in bytes; linked files
+are archived with this field specified as zero. @FIXME-xref{Modifiers}, in
+particular the @value{op-incremental} option.
+
+The @code{mtime} field is the modification time of the file at the time
+it was archived. It is the ASCII representation of the octal value of
+the last time the file was modified, represented as an integer number of
+seconds since January 1, 1970, 00:00 Coordinated Universal Time.
+
+The @code{chksum} field is the ASCII representation of the octal value
+of the simple sum of all bytes in the header block. Each 8-bit
+byte in the header is added to an unsigned integer, initialized to
+zero, the precision of which shall be no less than seventeen bits.
+When calculating the checksum, the @code{chksum} field is treated as
+if it were all blanks.
+
+The @code{typeflag} field specifies the type of file archived. If a
+particular implementation does not recognize or permit the specified
+type, the file will be extracted as if it were a regular file. As this
+action occurs, @code{tar} issues a warning to the standard error.
+
+The @code{atime} and @code{ctime} fields are used in making incremental
+backups; they store, respectively, the particular file's access time
+and last inode-change time.
+
+The @code{offset} is used by the @value{op-multi-volume} option, when
+making a multi-volume archive. The offset is number of bytes into
+the file that we need to restart at to continue the file on the next
+tape, i.e., where we store the location that a continued file is
+continued at.
+
+The following fields were added to deal with sparse files. A file
+is @dfn{sparse} if it takes in unallocated blocks which end up being
+represented as zeros, i.e., no useful data. A test to see if a file
+is sparse is to look at the number blocks allocated for it versus the
+number of characters in the file; if there are fewer blocks allocated
+for the file than would normally be allocated for a file of that
+size, then the file is sparse. This is the method @code{tar} uses to
+detect a sparse file, and once such a file is detected, it is treated
+differently from non-sparse files.
+
+Sparse files are often @code{dbm} files, or other database-type files
+which have data at some points and emptiness in the greater part of
+the file. Such files can appear to be very large when an @samp{ls
+-l} is done on them, when in truth, there may be a very small amount
+of important data contained in the file. It is thus undesirable
+to have @code{tar} think that it must back up this entire file, as
+great quantities of room are wasted on empty blocks, which can lead
+to running out of room on a tape far earlier than is necessary.
+Thus, sparse files are dealt with so that these empty blocks are
+not written to the tape. Instead, what is written to the tape is a
+description, of sorts, of the sparse file: where the holes are, how
+big the holes are, and how much data is found at the end of the hole.
+This way, the file takes up potentially far less room on the tape,
+and when the file is extracted later on, it will look exactly the way
+it looked beforehand. The following is a description of the fields
+used to handle a sparse file:
+
+The @code{sp} is an array of @code{struct sparse}. Each @code{struct
+sparse} contains two 12-character strings which represent an offset
+into the file and a number of bytes to be written at that offset.
+The offset is absolute, and not relative to the offset in preceding
+array element.
+
+The header can hold four of these @code{struct sparse} at the moment;
+if more are needed, they are not stored in the header.
+
+The @code{isextended} flag is set when an @code{extended_header}
+is needed to deal with a file. Note that this means that this flag
+can only be set when dealing with a sparse file, and it is only set
+in the event that the description of the file will not fit in the
+alloted room for sparse structures in the header. In other words,
+an extended_header is needed.
+
+The @code{extended_header} structure is used for sparse files which
+need more sparse structures than can fit in the header. The header can
+fit 4 such structures; if more are needed, the flag @code{isextended}
+gets set and the next block is an @code{extended_header}.
+
+Each @code{extended_header} structure contains an array of 21
+sparse structures, along with a similar @code{isextended} flag
+that the header had. There can be an indeterminate number of such
+@code{extended_header}s to describe a sparse file.
+
+@table @asis
+
+@item @code{REGTYPE}
+@itemx @code{AREGTYPE}
+These flags represent a regular file. In order to be compatible
+with older versions of @code{tar}, a @code{typeflag} value of
+@code{AREGTYPE} should be silently recognized as a regular file.
+New archives should be created using @code{REGTYPE}. Also, for
+backward compatibility, @code{tar} treats a regular file whose name
+ends with a slash as a directory.
+
+@item @code{LNKTYPE}
+This flag represents a file linked to another file, of any type,
+previously archived. Such files are identified in Unix by each
+file having the same device and inode number. The linked-to name is
+specified in the @code{linkname} field with a trailing null.
+
+@item @code{SYMTYPE}
+This represents a symbolic link to another file. The linked-to name
+is specified in the @code{linkname} field with a trailing null.
+
+@item @code{CHRTYPE}
+@itemx @code{BLKTYPE}
+These represent character special files and block special files
+respectively. In this case the @code{devmajor} and @code{devminor}
+fields will contain the major and minor device numbers respectively.
+Operating systems may map the device specifications to their own
+local specification, or may ignore the entry.
+
+@item @code{DIRTYPE}
+This flag specifies a directory or sub-directory. The directory
+name in the @code{name} field should end with a slash. On systems where
+disk allocation is performed on a directory basis, the @code{size} field
+will contain the maximum number of bytes (which may be rounded to
+the nearest disk block allocation unit) which the directory may
+hold. A @code{size} field of zero indicates no such limiting. Systems
+which do not support limiting in this manner should ignore the
+@code{size} field.
+
+@item @code{FIFOTYPE}
+This specifies a FIFO special file. Note that the archiving of a
+FIFO file archives the existence of this file and not its contents.
+
+@item @code{CONTTYPE}
+This specifies a contiguous file, which is the same as a normal
+file except that, in operating systems which support it, all its
+space is allocated contiguously on the disk. Operating systems
+which do not allow contiguous allocation should silently treat this
+type as a normal file.
+
+@item @code{A} @dots{} @code{Z}
+These are reserved for custom implementations. Some of these are
+used in the GNU modified format, as described below.
+
+@end table
+
+Other values are reserved for specification in future revisions of
+the P1003 standard, and should not be used by any @code{tar} program.
+
+The @code{magic} field indicates that this archive was output in
+the P1003 archive format. If this field contains @code{TMAGIC},
+the @code{uname} and @code{gname} fields will contain the ASCII
+representation of the owner and group of the file respectively.
+If found, the user and group IDs are used rather than the values in
+the @code{uid} and @code{gid} fields.
+
+For references, see ISO/IEC 9945-1:1990 or IEEE Std 1003.1-1990, pages
+169-173 (section 10.1) for @cite{Archive/Interchange File Format}; and
+IEEE Std 1003.2-1992, pages 380-388 (section 4.48) and pages 936-940
+(section E.4.48) for @cite{pax - Portable archive interchange}.
+
+@node Extensions, cpio, Standard, Formats
+@section GNU Extensions to the Archive Format
+@UNREVISED
+
+The GNU format uses additional file types to describe new types of
+files in an archive. These are listed below.
+
+@table @code
+@item GNUTYPE_DUMPDIR
+@itemx 'D'
+This represents a directory and a list of files created by the
+@value{op-incremental} option. The @code{size} field gives the total
+size of the associated list of files. Each file name is preceded by
+either a @samp{Y} (the file should be in this archive) or an @samp{N}.
+(The file is a directory, or is not stored in the archive.) Each file
+name is terminated by a null. There is an additional null after the
+last file name.
+
+@item GNUTYPE_MULTIVOL
+@itemx 'M'
+This represents a file continued from another volume of a multi-volume
+archive created with the @value{op-multi-volume} option. The original
+type of the file is not given here. The @code{size} field gives the
+maximum size of this piece of the file (assuming the volume does
+not end before the file is written out). The @code{offset} field
+gives the offset from the beginning of the file where this part of
+the file begins. Thus @code{size} plus @code{offset} should equal
+the original size of the file.
+
+@item GNUTYPE_SPARSE
+@itemx 'S'
+This flag indicates that we are dealing with a sparse file. Note
+that archiving a sparse file requires special operations to find
+holes in the file, which mark the positions of these holes, along
+with the number of bytes of data to be found after the hole.
+
+@item GNUTYPE_VOLHDR
+@itemx 'V'
+This file type is used to mark the volume header that was given with
+the @value{op-label} option when the archive was created. The @code{name}
+field contains the @code{name} given after the @value{op-label} option.
+The @code{size} field is zero. Only the first file in each volume
+of an archive should have this type.
+
+@end table
+
+You may have trouble reading a GNU format archive on a non-GNU
+system if the options @value{op-incremental}, @value{op-multi-volume},
+@value{op-sparse}, or @value{op-label} were used when writing the archive.
+In general, if @code{tar} does not use the GNU-added fields of the
+header, other versions of @code{tar} should be able to read the
+archive. Otherwise, the @code{tar} program will give an error, the
+most likely one being a checksum error.
+
+@node cpio, , Extensions, Formats
+@section Comparison of @code{tar} and @code{cpio}
+@UNREVISED
+
+@FIXME{Reorganize the following material}
+
+The @code{cpio} archive formats, like @code{tar}, do have maximum
+pathname lengths. The binary and old ASCII formats have a max path
+length of 256, and the new ASCII and CRC ASCII formats have a max
+path length of 1024. GNU @code{cpio} can read and write archives
+with arbitrary pathname lengths, but other @code{cpio} implementations
+may crash unexplainedly trying to read them.
+
+@code{tar} handles symbolic links in the form in which it comes in BSD;
+@code{cpio} doesn't handle symbolic links in the form in which it comes
+in System V prior to SVR4, and some vendors may have added symlinks
+to their system without enhancing @code{cpio} to know about them.
+Others may have enhanced it in a way other than the way I did it
+at Sun, and which was adopted by AT&T (and which is, I think, also
+present in the @code{cpio} that Berkeley picked up from AT&T and put
+into a later BSD release---I think I gave them my changes).
+
+(SVR4 does some funny stuff with @code{tar}; basically, its @code{cpio}
+can handle @code{tar} format input, and write it on output, and it
+probably handles symbolic links. They may not have bothered doing
+anything to enhance @code{tar} as a result.)
+
+@code{cpio} handles special files; traditional @code{tar} doesn't.
+
+@code{tar} comes with V7, System III, System V, and BSD source;
+@code{cpio} comes only with System III, System V, and later BSD
+(4.3-tahoe and later).
+
+@code{tar}'s way of handling multiple hard links to a file can handle
+file systems that support 32-bit inumbers (e.g., the BSD file system);
+@code{cpio}s way requires you to play some games (in its "binary"
+format, i-numbers are only 16 bits, and in its "portable ASCII" format,
+they're 18 bits---it would have to play games with the "file system ID"
+field of the header to make sure that the file system ID/i-number pairs
+of different files were always different), and I don't know which
+@code{cpio}s, if any, play those games. Those that don't might get
+confused and think two files are the same file when they're not, and
+make hard links between them.
+
+@code{tar}s way of handling multiple hard links to a file places only
+one copy of the link on the tape, but the name attached to that copy
+is the @emph{only} one you can use to retrieve the file; @code{cpio}s
+way puts one copy for every link, but you can retrieve it using any
+of the names.
+
+@quotation
+What type of check sum (if any) is used, and how is this calculated.
+@end quotation
+
+See the attached manual pages for @code{tar} and @code{cpio} format.
+@code{tar} uses a checksum which is the sum of all the bytes in the
+@code{tar} header for a file; @code{cpio} uses no checksum.
+
+@quotation
+If anyone knows why @code{cpio} was made when @code{tar} was present
+at the unix scene,
+@end quotation
+
+It wasn't. @code{cpio} first showed up in PWB/UNIX 1.0; no
+generally-available version of UNIX had @code{tar} at the time. I don't
+know whether any version that was generally available @emph{within AT&T}
+had @code{tar}, or, if so, whether the people within AT&T who did
+@code{cpio} knew about it.
+
+On restore, if there is a corruption on a tape @code{tar} will stop at
+that point, while @code{cpio} will skip over it and try to restore the
+rest of the files.
+
+The main difference is just in the command syntax and header format.
+
+@code{tar} is a little more tape-oriented in that everything is blocked
+to start on a record boundary.
+
+@quotation
+Is there any differences between the ability to recover crashed
+archives between the two of them. (Is there any chance of recovering
+crashed archives at all.)
+@end quotation
+
+Theoretically it should be easier under @code{tar} since the blocking
+lets you find a header with some variation of @samp{dd skip=@var{nn}}.
+However, modern @code{cpio}'s and variations have an option to just
+search for the next file header after an error with a reasonable chance
+of re-syncing. However, lots of tape driver software won't allow you to
+continue past a media error which should be the only reason for getting
+out of sync unless a file changed sizes while you were writing the
+archive.
+
+@quotation
+If anyone knows why @code{cpio} was made when @code{tar} was present
+at the unix scene, please tell me about this too.
+@end quotation
+
+Probably because it is more media efficient (by not blocking everything
+and using only the space needed for the headers where @code{tar}
+always uses 512 bytes per file header) and it knows how to archive
+special files.
+
+You might want to look at the freely available alternatives. The major
+ones are @code{afio}, GNU @code{tar}, and @code{pax}, each of which
+have their own extensions with some backwards compatibility.
+
+Sparse files were @code{tar}red as sparse files (which you can easily
+test, because the resulting archive gets smaller, and GNU @code{cpio}
+can no longer read it).
+
+@node Media, Index, Formats, Top
+@chapter Tapes and Other Archive Media
+@UNREVISED
+
+A few special cases about tape handling warrant more detailed
+description. These special cases are discussed below.
+
+Many complexities surround the use of @code{tar} on tape drives. Since
+the creation and manipulation of archives located on magnetic tape was
+the original purpose of @code{tar}, it contains many features making
+such manipulation easier.
+
+Archives are usually written on dismountable media---tape cartridges,
+mag tapes, or floppy disks.
+
+The amount of data a tape or disk holds depends not only on its size,
+but also on how it is formatted. A 2400 foot long reel of mag tape
+holds 40 megabytes of data when formated at 1600 bits per inch. The
+physically smaller EXABYTE tape cartridge holds 2.3 gigabytes.
+
+Magnetic media are re-usable---once the archive on a tape is no longer
+needed, the archive can be erased and the tape or disk used over.
+Media quality does deteriorate with use, however. Most tapes or disks
+should be disgarded when they begin to produce data errors. EXABYTE
+tape cartridges should be disgarded when they generate an @dfn{error
+count} (number of non-usable bits) of more than 10k.
+
+Magnetic media are written and erased using magnetic fields, and
+should be protected from such fields to avoid damage to stored data.
+Sticking a floppy disk to a filing cabinet using a magnet is probably
+not a good idea.
+
+@menu
+* Device:: Device selection and switching
+* Remote Tape Server::
+* Common Problems and Solutions::
+* Blocking:: Blocking
+* Many:: Many archives on one tape
+* Using Multiple Tapes:: Using Multiple Tapes
+* label:: Including a Label in the Archive
+* verify::
+* Write Protection::
+@end menu
+
+@node Device, Remote Tape Server, Media, Media
+@section Device Selection and Switching
+@UNREVISED
+
+@table @kbd
+@item -f [@var{hostname}:]@var{file}
+@itemx --file=[@var{hostname}:]@var{file}
+Use archive file or device @var{file} on @var{hostname}.
+@end table
+
+This option is used to specify the file name of the archive @code{tar}
+works on.
+
+If the file name is @samp{-}, @code{tar} reads the archive from standard
+input (when listing or extracting), or writes it to standard output
+(when creating). If the @samp{-} file name is given when updating an
+archive, @code{tar} will read the original archive from its standard
+input, and will write the entire new archive to its standard output.
+
+If the file name contains a @samp{:}, it is interpreted as
+@samp{hostname:file name}. If the @var{hostname} contains an @dfn{at}
+sign (@kbd{@@}), it is treated as @samp{user@@hostname:file name}. In
+either case, @code{tar} will invoke the command @code{rsh} (or
+@code{remsh}) to start up an @file{/etc/rmt} on the remote machine. If
+you give an alternate login name, it will be given to the @code{rsh}.
+Naturally, the remote machine must have an executable @file{/etc/rmt}.
+This program is free software from the University of California, and a
+copy of the source code can be found with the sources for @code{tar};
+it's compiled and installed by default.
+
+If this option is not given, but the environment variable @code{TAPE} is
+set, its value is used; otherwise, old versions of @code{tar} used a default
+archive name (which was picked when @code{tar} was compiled). The
+default is normally set up to be the @dfn{first} tape drive or other
+transportable I/O medium on the system.
+
+Starting with version 1.11.5, GNU @code{tar} uses standard input and
+standard output as the default device, and I will not try anymore
+supporting automatic device detection at installation time. This was
+failing really in too many cases, it was hopeless. This is now
+completely left to the installer to override standard input and standard
+output for default device, if this seems preferrable to him/her.
+Further, I think @emph{most} actual usages of @code{tar} are done with
+pipes or disks, not really tapes, cartridges or diskettes.
+
+Some users think that using standard input and output is running
+after trouble. This could lead to a nasty surprise on your screen if
+you forget to specify an output file name---especially if you are going
+through a network or terminal server capable of buffering large amounts
+of output. We had so many bug reports in that area of configuring
+default tapes automatically, and so many contradicting requests, that
+we finally consider the problem to be portably intractable. We could
+of course use something like @samp{/dev/tape} as a default, but this
+is @emph{also} running after various kind of trouble, going from hung
+processes to accidental destruction of real tapes. After having seen
+all this mess, using standard input and output as a default really
+sounds like the only clean choice left, and a very useful one too.
+
+GNU @code{tar} reads and writes archive in records, I suspect this is the
+main reason why block devices are preferred over character devices.
+Most probably, block devices are more efficient too. The installer
+could also check for @samp{DEFTAPE} in @file{<sys/mtio.h>}.
+
+@table @kbd
+@item --force-local
+Archive file is local even if it contains a colon.
+
+@item --rsh-command=@var{command}
+Use remote @var{command} instead of @code{rsh}. This option exists
+so that people who use something other than the standard @code{rsh}
+(e.g., a Kerberized @code{rsh}) can access a remote device.
+
+When this command is not used, the shell command found when
+the @code{tar} program was installed is used instead. This is
+the first found of @file{/usr/ucb/rsh}, @file{/usr/bin/remsh},
+@file{/usr/bin/rsh}, @file{/usr/bsd/rsh} or @file{/usr/bin/nsh}.
+The installer may have overriden this by defining the environment
+variable @code{RSH} @emph{at installation time}.
+
+@item -[0-7][lmh]
+Specify drive and density.
+
+@item -M
+@itemx --multi-volume
+Create/list/extract multi-volume archive.
+
+This option causes @code{tar} to write a @dfn{multi-volume} archive---one
+that may be larger than will fit on the medium used to hold it.
+@xref{Multi-Volume Archives}.
+
+@item -L @var{num}
+@itemx --tape-length=@var{num}
+Change tape after writing @var{num} x 1024 bytes.
+
+This option might be useful when your tape drivers do not properly
+detect end of physical tapes. By being slightly conservative on the
+maximum tape length, you might avoid the problem entirely.
+
+@item -F @var{file}
+@itemx --info-script=@var{file}
+@itemx --new-volume-script=@var{file}
+Execute @file{file} at end of each tape. This implies
+@value{op-multi-volume}.
+@end table
+
+@node Remote Tape Server, Common Problems and Solutions, Device, Media
+@section The Remote Tape Server
+
+@cindex remote tape drive
+@pindex rmt
+In order to access the tape drive on a remote machine, @code{tar}
+uses the remote tape server written at the University of California at
+Berkeley. The remote tape server must be installed as @file{/etc/rmt}
+on any machine whose tape drive you want to use. @code{tar} calls
+@file{/etc/rmt} by running an @code{rsh} or @code{remsh} to the remote
+machine, optionally using a different login name if one is supplied.
+
+A copy of the source for the remote tape server is provided. It is
+Copyright @copyright{} 1983 by the Regents of the University of
+California, but can be freely distributed. Instructions for compiling
+and installing it are included in the @file{Makefile}.
+
+@cindex absolute file names
+Unless you use the @value{op-absolute-names} option, GNU @code{tar} will
+not allow you to create an archive that contains absolute file names
+(a file name beginning with @samp{/}.) If you try, @code{tar} will
+automatically remove the leading @samp{/} from the file names it
+stores in the archive. It will also type a warning message telling
+you what it is doing.
+
+When reading an archive that was created with a different @code{tar}
+program, GNU @code{tar} automatically extracts entries in the archive
+which have absolute file names as if the file names were not absolute.
+This is an important feature. A visitor here once gave a
+@code{tar} tape to an operator to restore; the operator used Sun @code{tar}
+instead of GNU @code{tar}, and the result was that it replaced large
+portions of our @file{/bin} and friends with versions from the tape;
+needless to say, we were unhappy about having to recover the file system
+from backup tapes.
+
+For example, if the archive contained a file @file{/usr/bin/computoy},
+GNU @code{tar} would extract the file to @file{usr/bin/computoy},
+relative to the current directory. If you want to extract the files in
+an archive to the same absolute names that they had when the archive
+was created, you should do a @samp{cd /} before extracting the files
+from the archive, or you should either use the @value{op-absolute-names}
+option, or use the command @samp{tar -C / @dots{}}.
+
+@cindex Ultrix 3.1 and write failure
+Some versions of Unix (Ultrix 3.1 is know to have this problem),
+can claim that a short write near the end of a tape succeeded,
+when it actually failed. This will result in the -M option not
+working correctly. The best workaround at the moment is to use a
+significantly larger blocking factor than the default 20.
+
+In order to update an archive, @code{tar} must be able to backspace the
+archive in order to reread or rewrite a record that was just read (or
+written). This is currently possible only on two kinds of files: normal
+disk files (or any other file that can be backspaced with @samp{lseek}),
+and industry-standard 9-track magnetic tape (or any other kind of tape
+that can be backspaced with the @code{MTIOCTOP} @code{ioctl}.
+
+This means that the @value{op-append}, @value{op-update},
+@value{op-concatenate}, and @value{op-delete} commands will not work on any
+other kind of file. Some media simply cannot be backspaced, which
+means these commands and options will never be able to work on them.
+These non-backspacing media include pipes and cartridge tape drives.
+
+Some other media can be backspaced, and @code{tar} will work on them
+once @code{tar} is modified to do so.
+
+Archives created with the @value{op-multi-volume}, @value{op-label}, and
+@value{op-incremental} options may not be readable by other version
+of @code{tar}. In particular, restoring a file that was split over
+a volume boundary will require some careful work with @code{dd}, if
+it can be done at all. Other versions of @code{tar} may also create
+an empty file whose name is that of the volume header. Some versions
+of @code{tar} may create normal files instead of directories archived
+with the @value{op-incremental} option.
+
+@node Common Problems and Solutions, Blocking, Remote Tape Server, Media
+@section Some Common Problems and their Solutions
+
+@ifclear PUBLISH
+
+@format
+errors from system:
+permission denied
+no such file or directory
+not owner
+
+errors from @code{tar}:
+directory checksum error
+header format error
+
+errors from media/system:
+i/o error
+device busy
+@end format
+
+@end ifclear
+
+@node Blocking, Many, Common Problems and Solutions, Media
+@section Blocking
+@UNREVISED
+
+@dfn{Block} and @dfn{record} terminology is rather confused, and it
+is also confusing to the expert reader. On the other hand, readers
+who are new to the field have a fresh mind, and they may safely skip
+the next two paragraphs, as the remainder of this manual uses those
+two terms in a quite consistent way.
+
+John Gilmore, the writer of the public domain @code{tar} from which
+GNU @code{tar} was originally derived, wrote (June 1995):
+
+@quotation
+The nomenclature of tape drives comes from IBM, where I believe
+they were invented for the IBM 650 or so. On IBM mainframes, what
+is recorded on tape are tape blocks. The logical organization of
+data is into records. There are various ways of putting records into
+blocks, including @code{F} (fixed sized records), @code{V} (variable
+sized records), @code{FB} (fixed blocked: fixed size records, @var{n}
+to a block), @code{VB} (variable size records, @var{n} to a block),
+@code{VSB} (variable spanned blocked: variable sized records that can
+occupy more than one block), etc. The @code{JCL} @samp{DD RECFORM=}
+parameter specified this to the operating system.
+
+The Unix man page on @code{tar} was totally confused about this.
+When I wrote @code{PD TAR}, I used the historically correct terminology
+(@code{tar} writes data records, which are grouped into blocks).
+It appears that the bogus terminology made it into POSIX (no surprise
+here), and now Fran@,{c}ois has migrated that terminology back
+into the source code too.
+@end quotation
+
+The term @dfn{physical block} means the basic transfer chunk from or
+to a device, after which reading or writing may stop without anything
+being lost. In this manual, the term @dfn{block} usually refers to
+a disk physical block, @emph{assuming} that each disk block is 512
+bytes in length. It is true that some disk devices have different
+physical blocks, but @code{tar} ignore these differences in its own
+format, which is meant to be portable, so a @code{tar} block is always
+512 bytes in length, and @dfn{block} always mean a @code{tar} block.
+The term @dfn{logical block} often represents the basic chunk of
+allocation of many disk blocks as a single entity, which the operating
+system treats somewhat atomically; this concept is only barely used
+in GNU @code{tar}.
+
+The term @dfn{physical record} is another way to speak of a physical
+block, those two terms are somewhat interchangeable. In this manual,
+the term @dfn{record} usually refers to a tape physical block,
+@emph{assuming} that the @code{tar} archive is kept on magnetic tape.
+It is true that archives may be put on disk or used with pipes,
+but nevertheless, @code{tar} tries to read and write the archive one
+@dfn{record} at a time, whatever the medium in use. One record is made
+up of an integral number of blocks, and this operation of putting many
+disk blocks into a single tape block is called @dfn{reblocking}, or
+more simply, @dfn{blocking}. The term @dfn{logical record} refers to
+the logical organization of many characters into something meaningful
+to the application. The term @dfn{unit record} describes a small set
+of characters which are transmitted whole to or by the application,
+and often refers to a line of text. Those two last terms are unrelated
+to what we call a @dfn{record} in GNU @code{tar}.
+
+When writing to tapes, @code{tar} writes the contents of the archive
+in chunks known as @dfn{records}. To change the default blocking
+factor, use the @value{op-blocking-factor} option. Each record will
+then be composed of @var{512-size} blocks. (Each @code{tar} block is
+512 bytes. @xref{Standard}.) Each file written to the archive uses
+at least one full record. As a result, using a larger record size
+can result in more wasted space for small files. On the other hand, a
+larger record size can often be read and written much more efficiently.
+
+Further complicating the problem is that some tape drives ignore the
+blocking entirely. For these, a larger record size can still improve
+performance (because the software layers above the tape drive still
+honor the blocking), but not as dramatically as on tape drives that
+honor blocking.
+
+When reading an archive, @code{tar} can usually figure out the record
+size on itself. When this is the case, and a non-standard record size
+was used when the archive was created, @code{tar} will print a message
+about a non-standard blocking factor, and then operate normally. On
+some tape devices, however, @code{tar} cannot figure out the record size
+itself. On most of those, you can specify a blocking factor (with
+@value{op-blocking-factor}) larger than the actual blocking factor, and then use
+the @value{op-read-full-records} option. (If you specify a blocking factor
+with @value{op-blocking-factor} and don't use the @value{op-read-full-records}
+option, then @code{tar} will not attempt to figure out the recording size
+itself.) On some devices, you must always specify the record size
+exactly with @value{op-blocking-factor} when reading, because @code{tar} cannot
+figure it out. In any case, use @value{op-list} before doing any
+extractions to see whether @code{tar} is reading the archive correctly.
+
+@code{tar} blocks are all fixed size (512 bytes), and its scheme for
+putting them into records is to put a whole number of them (one or
+more) into each record. @code{tar} records are all the same size;
+at the end of the file there's a block containing all zeros, which
+is how you tell that the remainder of the last record(s) are garbage.
+
+In a standard @code{tar} file (no options), the block size is 512
+and the record size is 10240, for a blocking factor of 20. What the
+@value{op-blocking-factor} option does is sets the blocking factor,
+changing the record size while leaving the block size at 512 bytes.
+20 was fine for ancient 800 or 1600 bpi reel-to-reel tape drives;
+most tape drives these days prefer much bigger records in order to
+stream and not waste tape. When writing tapes for myself, some tend
+to use a factor of the order of 2048, say, giving a record size of
+around one megabyte.
+
+If you use a blocking factor larger than 20, older @code{tar} programs
+might not be able to read the archive, so we recommend this as a limit
+to use in practice. GNU @code{tar}, however, will support arbitrarily
+large record sizes, limited only by the amount of virtual memory or the
+physical characteristics of the tape device.
+
+@menu
+* Format Variations:: Format Variations
+* Blocking Factor:: The Blocking Factor of an Archive
+@end menu
+
+@node Format Variations, Blocking Factor, Blocking, Blocking
+@subsection Format Variations
+@cindex Format Parameters
+@cindex Format Options
+@cindex Options, archive format specifying
+@cindex Options, format specifying
+@UNREVISED
+
+Format parameters specify how an archive is written on the archive
+media. The best choice of format parameters will vary depending on
+the type and number of files being archived, and on the media used to
+store the archive.
+
+To specify format parameters when accessing or creating an archive,
+you can use the options described in the following sections.
+If you do not specify any format parameters, @code{tar} uses
+default parameters. You cannot modify a compressed archive.
+If you create an archive with the @value{op-blocking-factor} option
+specified (@value{pxref-blocking-factor}), you must specify that
+blocking-factor when operating on the archive. @xref{Formats}, for other
+examples of format parameter considerations.
+
+@node Blocking Factor, , Format Variations, Blocking
+@subsection The Blocking Factor of an Archive
+@cindex Blocking Factor
+@cindex Record Size
+@cindex Number of blocks per record
+@cindex Number of bytes per record
+@cindex Bytes per record
+@cindex Blocks per record
+@UNREVISED
+
+The data in an archive is grouped into blocks, which are 512 bytes.
+Blocks are read and written in whole number multiples called
+@dfn{records}. The number of blocks in a record (ie. the size of a
+record in units of 512 bytes) is called the @dfn{blocking factor}.
+The @value{op-blocking-factor} option specifies the blocking factor of
+an archive. The default blocking factor is typically 20 (ie.@:
+10240 bytes), but can be specified at installation. To find out
+the blocking factor of an existing archive, use @samp{tar --list
+--file=@var{archive-name}}. This may not work on some devices.
+
+Records are separated by gaps, which waste space on the archive media.
+If you are archiving on magnetic tape, using a larger blocking factor
+(and therefore larger records) provides faster throughput and allows you
+to fit more data on a tape (because there are fewer gaps). If you are
+archiving on cartridge, a very large blocking factor (say 126 or more)
+greatly increases performance. A smaller blocking factor, on the other
+hand, may be usefull when archiving small files, to avoid archiving lots
+of nulls as @code{tar} fills out the archive to the end of the record.
+In general, the ideal record size depends on the size of the
+inter-record gaps on the tape you are using, and the average size of the
+files you are archiving. @xref{create}, for information on
+writing archives.
+
+@FIXME{Need example of using a cartridge with blocking factor=126 or more.}
+
+Archives with blocking factors larger than 20 cannot be read
+by very old versions of @code{tar}, or by some newer versions
+of @code{tar} running on old machines with small address spaces.
+With GNU @code{tar}, the blocking factor of an archive is limited
+only by the maximum record size of the device containing the archive,
+or by the amount of available virtual memory.
+
+Also, on some systems, not using adequate blocking factors, as sometimes
+imposed by the device drivers, may yield unexpected diagnostics. For
+example, this has been reported:
+
+@example
+Cannot write to /dev/dlt: Invalid argument
+@end example
+
+@noindent
+In such cases, it sometimes happen that the @code{tar} bundled by the
+system is aware of block size idiosyncrasies, while GNU @code{tar} requires
+an explicit specification for the block size, which it cannot guess.
+This yields some people to consider GNU @code{tar} is misbehaving, because
+by comparison, @cite{the bundle @code{tar} works OK}. Adding @w{@kbd{-b
+256}}, for example, might resolve the problem.
+
+If you use a non-default blocking factor when you create an archive, you
+must specify the same blocking factor when you modify that archive. Some
+archive devices will also require you to specify the blocking factor when
+reading that archive, however this is not typically the case. Usually, you
+can use @value{op-list} without specifying a blocking factor---@code{tar}
+reports a non-default record size and then lists the archive members as
+it would normally. To extract files from an archive with a non-standard
+blocking factor (particularly if you're not sure what the blocking factor
+is), you can usually use the @value{op-read-full-records} option while
+specifying a blocking factor larger then the blocking factor of the archive
+(ie. @samp{tar --extract --read-full-records --blocking-factor=300}.
+@xref{list}, for more information on the @value{op-list}
+operation. @xref{Reading}, for a more detailed explanation of that option.
+
+@table @kbd
+@item --blocking-factor=@var{number}
+@itemx -b @var{number}
+Specifies the blocking factor of an archive. Can be used with any
+operation, but is usually not necessary with @value{op-list}.
+@end table
+
+Device blocking
+
+@table @kbd
+@item -b @var{blocks}
+@itemx --blocking-factor=@var{blocks}
+Set record size to @math{@var{blocks} * 512} bytes.
+
+This option is used to specify a @dfn{blocking factor} for the archive.
+When reading or writing the archive, @code{tar}, will do reads and writes
+of the archive in records of @math{@var{block}*512} bytes. This is true
+even when the archive is compressed. Some devices requires that all
+write operations be a multiple of a certain size, and so, @code{tar}
+pads the archive out to the next record boundary.
+
+The default blocking factor is set when @code{tar} is compiled, and is
+typically 20. Blocking factors larger than 20 cannot be read by very
+old versions of @code{tar}, or by some newer versions of @code{tar}
+running on old machines with small address spaces.
+
+With a magnetic tape, larger records give faster throughput and fit
+more data on a tape (because there are fewer inter-record gaps).
+If the archive is in a disk file or a pipe, you may want to specify
+a smaller blocking factor, since a large one will result in a large
+number of null bytes at the end of the archive.
+
+When writing cartridge or other streaming tapes, a much larger
+blocking factor (say 126 or more) will greatly increase performance.
+However, you must specify the same blocking factor when reading or
+updating the archive.
+
+Apparently, Exabyte drives have a physical block size of 8K bytes.
+If we choose our blocksize as a multiple of 8k bytes, then the problem
+seems to dissapper. Id est, we are using block size of 112 right
+now, and we haven't had the problem since we switched@dots{}
+
+With GNU @code{tar} the blocking factor is limited only by the maximum
+record size of the device containing the archive, or by the amount of
+available virtual memory.
+
+However, deblocking or reblocking is virtually avoided in a special
+case which often occurs in practice, but which requires all the
+following conditions to be simultaneously true:
+@itemize @bullet
+@item
+the archive is subject to a compression option,
+@item
+the archive is not handled through standard input or output, nor
+redirected nor piped,
+@item
+the archive is directly handled to a local disk, instead of any special
+device,
+@item
+@value{op-blocking-factor} is not explicitely specified on the @code{tar}
+invocation.
+@end itemize
+
+In previous versions of GNU @code{tar}, the @samp{--compress-block}
+option (or even older: @samp{--block-compress}) was necessary to
+reblock compressed archives. It is now a dummy option just asking
+not to be used, and otherwise ignored. If the output goes directly
+to a local disk, and not through stdout, then the last write is
+not extended to a full record size. Otherwise, reblocking occurs.
+Here are a few other remarks on this topic:
+
+@itemize @bullet
+
+@item
+@code{gzip} will complain about trailing garbage if asked to
+uncompress a compressed archive on tape, there is an option to turn
+the message off, but it breaks the regularity of simply having to use
+@samp{@var{prog} -d} for decompression. It would be nice if gzip was
+silently ignoring any number of trailing zeros. I'll ask Jean-loup
+Gailly, by sending a copy of this message to him.
+
+@item
+@code{compress} does not show this problem, but as Jean-loup pointed
+out to Michael, @samp{compress -d} silently adds garbage after
+the result of decompression, which tar ignores because it already
+recognized its end-of-file indicator. So this bug may be safely
+ignored.
+
+@item
+@samp{gzip -d -q} will be silent about the trailing zeros indeed,
+but will still return an exit status of 2 which tar reports in turn.
+@code{tar} might ignore the exit status returned, but I hate doing
+that, as it weakens the protection @code{tar} offers users against
+other possible problems at decompression time. If @code{gzip} was
+silently skipping trailing zeros @emph{and} also avoiding setting the
+exit status in this innocuous case, that would solve this situation.
+
+@item
+@code{tar} should become more solid at not stopping to read a pipe at
+the first null block encountered. This inelegantly breaks the pipe.
+@code{tar} should rather drain the pipe out before exiting itself.
+@end itemize
+
+@item -i
+@itemx --ignore-zeros
+Ignore blocks of zeros in archive (means EOF).
+
+The @value{op-ignore-zeros} option causes @code{tar} to ignore blocks
+of zeros in the archive. Normally a block of zeros indicates the
+end of the archive, but when reading a damaged archive, or one which
+was created by @code{cat}-ing several archives together, this option
+allows @code{tar} to read the entire archive. This option is not on
+by default because many versions of @code{tar} write garbage after
+the zeroed blocks.
+
+Note that this option causes @code{tar} to read to the end of the
+archive file, which may sometimes avoid problems when multiple files
+are stored on a single physical tape.
+
+@item -B
+@itemx --read-full-records
+Reblock as we read (for reading 4.2BSD pipes).
+
+If @value{op-read-full-records} is used, @code{tar} will not panic if an
+attempt to read a record from the archive does not return a full record.
+Instead, @code{tar} will keep reading until it has obtained a full
+record.
+
+This option is turned on by default when @code{tar} is reading
+an archive from standard input, or from a remote machine. This is
+because on BSD Unix systems, a read of a pipe will return however
+much happens to be in the pipe, even if it is less than @code{tar}
+requested. If this option was not used, @code{tar} would fail as
+soon as it read an incomplete record from the pipe.
+
+This option is also useful with the commands for updating an archive.
+
+@end table
+
+Tape blocking
+
+@FIXME{Appropriate options should be moved here from elsewhere.}
+
+@cindex blocking factor
+@cindex tape blocking
+
+When handling various tapes or cartridges, you have to take care of
+selecting a proper blocking, that is, the number of disk blocks you
+put together as a single tape block on the tape, without intervening
+tape gaps. A @dfn{tape gap} is a small landing area on the tape
+with no information on it, used for decelerating the tape to a
+full stop, and for later regaining the reading or writing speed.
+When the tape driver starts reading a record, the record has to
+be read whole without stopping, as a tape gap is needed to stop the
+tape motion without loosing information.
+
+@cindex Exabyte blocking
+@cindex DAT blocking
+Using higher blocking (putting more disk blocks per tape block) will use
+the tape more efficiently as there will be less tape gaps. But reading
+such tapes may be more difficult for the system, as more memory will be
+required to receive at once the whole record. Further, if there is a
+reading error on a huge record, this is less likely that the system will
+succeed in recovering the information. So, blocking should not be too
+low, nor it should be too high. @code{tar} uses by default a blocking of
+20 for historical reasons, and it does not really matter when reading or
+writing to disk. Current tape technology would easily accomodate higher
+blockings. Sun recommends a blocking of 126 for Exabytes and 96 for DATs.
+We were told that for some DLT drives, the blocking should be a multiple
+of 4Kb, preferably 64Kb (@w{@kbd{-b 128}}) or 256 for decent performance.
+Other manufacturers may use different recommendations for the same tapes.
+This might also depends of the buffering techniques used inside modern
+tape controllers. Some imposes a minimum blocking, or a maximum blocking.
+Others request blocking to be some exponent of two.
+
+So, there is no fixed rule for blocking. But blocking at read time
+should ideally be the same as blocking used at write time. At one place
+I know, with a wide variety of equipment, they found it best to use a
+blocking of 32 to guarantee that their tapes are fully interchangeable.
+
+I was also told that, for recycled tapes, prior erasure (by the same
+drive unit that will be used to create the archives) sometimes lowers
+the error rates observed at rewriting time.
+
+I might also use @samp{--number-blocks} instead of
+@samp{--block-number}, so @samp{--block} will then expand to
+@samp{--blocking-factor} unambiguously.
+
+@node Many, Using Multiple Tapes, Blocking, Media
+@section Many Archives on One Tape
+
+@FIXME{Appropriate options should be moved here from elsewhere.}
+
+@findex ntape @r{device}
+Most tape devices have two entries in the @file{/dev} directory, or
+entries that come in pairs, which differ only in the minor number for
+this device. Let's take for example @file{/dev/tape}, which often
+points to the only or usual tape device of a given system. There might
+be a corresponding @file{/dev/nrtape} or @file{/dev/ntape}. The simpler
+name is the @emph{rewinding} version of the device, while the name
+having @samp{nr} in it is the @emph{no rewinding} version of the same
+device.
+
+A rewinding tape device will bring back the tape to its beginning point
+automatically when this device is opened or closed. Since @code{tar}
+opens the archive file before using it and closes it afterwards, this
+means that a simple:
+
+@example
+$ @kbd{tar cf /dev/tape @var{directory}}
+@end example
+
+@noindent
+will reposition the tape to its beginning both prior and after saving
+@var{directory} contents to it, thus erasing prior tape contents and
+making it so that any subsequent write operation will destroy what has
+just been saved.
+
+@cindex tape positioning
+So, a rewinding device is normally meant to hold one and only one file.
+If you want to put more than one @code{tar} archive on a given tape, you
+will need to avoid using the rewinding version of the tape device. You
+will also have to pay special attention to tape positioning. Errors in
+positionning may overwrite the valuable data already on your tape. Many
+people, burnt by past experiences, will only use rewinding devices and
+limit themselves to one file per tape, precisely to avoid the risk of
+such errors. Be fully aware that writing at the wrong position on a
+tape loses all information past this point and most probably until the
+end of the tape, and this destroyed information @emph{cannot} be
+recovered.
+
+To save @var{directory-1} as a first archive at the beginning of a
+tape, and leave that tape ready for a second archive, you should use:
-@node Media, Quick Reference, Backups and Restoration, Top
-@chapter Tapes and Other Archive Media
+@example
+$ @kbd{mt -f /dev/nrtape rewind}
+$ @kbd{tar cf /dev/nrtape @var{directory-1}}
+@end example
-Archives are usually written on dismountable media---tape cartridges,
-mag tapes, or floppy disks.
+@cindex tape marks
+@dfn{Tape marks} are special magnetic patterns written on the tape
+media, which are later recognizable by the reading hardware. These
+marks are used after each file, when there are many on a single tape.
+An empty file (that is to say, two tape marks in a row) signal the
+logical end of the tape, after which no file exist. Usually,
+non-rewinding tape device drivers will react to the close request issued
+by @code{tar} by first writing two tape marks after your archive, and by
+backspacing over one of these. So, if you remove the tape at that time
+from the tape drive, it is properly terminated. But if you write
+another file at the current position, the second tape mark will be
+erased by the new information, leaving only one tape mark between files.
+
+So, you may now save @var{directory-2} as a second archive after the
+first on the same tape by issuing the command:
-The amount of data a tape or disk holds depends not only on its size,
-but also on how it is formatted. A 2400 foot long reel of mag tape
-holds 40 megabytes of data when formated at 1600 bits per inch. The
-physically smaller EXABYTE tape cartridge holds 2.3 gigabytes.
+@example
+$ @kbd{tar cf /dev/nrtape @var{directory-2}}
+@end example
-Magnetic media are re-usable---once the archive on a tape is no longer
-needed, the archive can be erased and the tape or disk used over.
-Media quality does deteriorate with use, however. Most tapes or disks
-should be disgarded when they begin to produce data errors. EXABYTE
-tape cartridges should be disgarded when they generate an @dfn{error
-count} (number of non-usable bits) of more than 10k.
+@noindent
+and so on for all the archives you want to put on the same tape.
-Magnetic media are written and erased using magnetic fields, and
-should be protected from such fields to avoid damage to stored data.
-Sticking a floppy disk to a filing cabinet using a magnet is probably
-not a good idea.
+Another usual case is that you do not write all the archives the same
+day, and you need to remove and store the tape between two archive
+sessions. In general, you must remember how many files are already
+saved on your tape. Suppose your tape already has 16 files on it, and
+that you are ready to write the 17th. You have to take care of skipping
+the first 16 tape marks before saving @var{directory-17}, say, by using
+these commands:
+
+@example
+$ @kbd{mt -f /dev/nrtape rewind}
+$ @kbd{mt -f /dev/nrtape fsf 16}
+$ @kbd{tar cf /dev/nrtape @var{directory-17}}
+@end example
+In all the previous examples, we put aside blocking considerations, but
+you should do the proper things for that as well. @xref{Blocking}.
@menu
-* Write Protection:: Write Protection
* Tape Positioning:: Tape Positions and Tape Marks
+* mt:: The @code{mt} Utility
@end menu
-@node Write Protection, Tape Positioning, Media, Media
-@section Write Protection
-
-All tapes and disks can be @dfn{write protected}, to protect data on
-them from being changed. Once an archive is written, you should write
-protect the media to prevent the archive from being accidently
-overwritten or deleted. (This will protect the archive from being
-changed with a tape or floppy drive---it will not protect it from
-magnet fields or other physical hazards).
-
-The write protection device itself is usually an integral part of the
-physical media, and can be a two position (write enabled/write
-disabled) switch, a notch which can be popped out or covered, a ring
-which can be removed from the center of a tape reel, or some other
-changeable feature.
-
-@node Tape Positioning, , Write Protection, Media
-@section Tape Positions and Tape Marks
+@node Tape Positioning, mt, Many, Many
+@subsection Tape Positions and Tape Marks
+@UNREVISED
Just as archives can store more than one file from the file system,
tapes can store more than one archive file. To keep track of where
archive media. Tape drives write one tape mark between files,
two at the end of all the file entries.
-If you think of data as a series of "0000"'s, and tape marks as "x"'s,
-a tape might look like the following:
+If you think of data as a series of records "rrrr"'s, and tape marks as
+"*"'s, a tape might look like the following:
@example
-0000x000000x00000x00x00000xx-------------------------
+rrrr*rrrrrr*rrrrr*rr*rrrrr**-------------------------
@end example
Tape devices read and write tapes using a read/write @dfn{tape
-head}---a physical part of the device which can only access one point
-on the tape at a time. When you use @code{tar} to read or write
-archive data from a tape device, the device will begin reading or
-writing from wherever on the tape the tape head happens to be,
-regardless of which archive or what part of the archive the tape head
-is on. Before writing an archive, you should make sure that no data
-on the tape will be overwritten (unless it is no longer needed).
+head}---a physical part of the device which can only access one
+point on the tape at a time. When you use @code{tar} to read or
+write archive data from a tape device, the device will begin reading
+or writing from wherever on the tape the tape head happens to be,
+regardless of which archive or what part of the archive the tape
+head is on. Before writing an archive, you should make sure that no
+data on the tape will be overwritten (unless it is no longer needed).
Before reading an archive, you should make sure the tape head is at
the beginning of the archive you want to read. (The @code{restore}
-script will find the archive automatically. @xref{Scripted
-Restoration}). @xref{mt}, for an explanation of the tape moving
-utility.
+script will find the archive automatically. @FIXME{There is no such
+restore script!}. @FIXME-xref{Scripted Restoration}). @xref{mt}, for
+an explanation of the tape moving utility.
If you want to add new archive file entries to a tape, you should
advance the tape to the end of the existing file entries, backspace
following:
@example
-0000x000000x00000x00x00000x000x0000xx----------------
+rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**----------------
@end example
-@menu
-* mt:: The @code{mt} Utility
-@end menu
-
-@node mt, , Tape Positioning, Tape Positioning
+@node mt, , Tape Positioning, Many
@subsection The @code{mt} Utility
+@UNREVISED
-<<< is it true that this only works on non-block devices? should
-<<< explain the difference, xref to block-size (fixed or variable).
+@FIXME{Is it true that this only works on non-block devices?
+should explain the difference, (fixed or variable).}
+@value{xref-blocking-factor}.
You can use the @code{mt} utility to advance or rewind a tape past a
-specified number of archive files on the tape. This will allow you to
-move to the beginning of an archive before extracting or reading it,
-or to the end of all the archives before writing a new one.
-@c why isn't there an "advance 'til you find two tape marks together"?
+specified number of archive files on the tape. This will allow you
+to move to the beginning of an archive before extracting or reading
+it, or to the end of all the archives before writing a new one.
+@FIXME{Why isn't there an "advance 'til you find two tape marks
+together"?}
The syntax of the @code{mt} command is:
@example
-mt [-f @var{tapename}] @var{operation} [@var{number}]
+@kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]}
@end example
where @var{tapename} is the name of the tape device, @var{number} is
the number of times an operation is performed (with a default of one),
and @var{operation} is one of the following:
-@table @code
+@FIXME{is there any use for record operations?}
+
+@table @kbd
@item eof
@itemx weof
Writes @var{number} tape marks at the current position on the tape.
-
-@item fsf
+@item fsf
Moves tape position forward @var{number} files.
-
@item bsf
Moves tape position back @var{number} files.
-
@item rewind
Rewinds the tape. (Ignores @var{number}).
-
@item offline
@itemx rewoff1
Rewinds the tape and takes the tape device off-line. (Ignores @var{number}).
-
@item status
Prints status information about the tape unit.
+
@end table
-<<< is there a better way to frob the spacing on the list? -ringo
+
+@FIXME{Is there a better way to frob the spacing on the list?}
If you don't specify a @var{tapename}, @code{mt} uses the environment
variable TAPE; if TAPE does not exist, @code{mt} uses the device
successful, 1 if the command was unrecognized, and 2 if an operation
failed.
-@c <<< new node on how to find an archive? -ringo
-If you use @code{tar +extract} with the
-@samp{+label=@var{archive-name}} option specified, @code{tar} will
-read an archive label (the tape head has to be positioned on it) and
-print an error if the archive label doesn't match the
+@FIXME{New node on how to find an archive?}
+
+If you use @value{op-extract} with the @value{op-label} option specified,
+@code{tar} will read an archive label (the tape head has to be positioned
+on it) and print an error if the archive label doesn't match the
@var{archive-name} specified. @var{archive-name} can be any regular
expression. If the labels match, @code{tar} extracts the archive.
-@xref{Archive Label}. @xref{Matching Format Parameters}.
-<<< fix cross references
-
-@code{tar +list +label} will cause @code{tar} to print the label.
-
-@c <<< MIB -- program to list all the labels on a tape?
+@value{xref-label}. @FIXME-xref{Matching Format Parameters}.
+@FIXME{fix cross references} @samp{tar --list --label} will cause
+@code{tar} to print the label.
+
+@FIXME{Program to list all the labels on a tape?}
+
+@node Using Multiple Tapes, label, Many, Media
+@section Using Multiple Tapes
+@UNREVISED
+
+Often you might want to write a large archive, one larger than will fit
+on the actual tape you are using. In such a case, you can run multiple
+@code{tar} commands, but this can be inconvenient, particularly if you
+are using options like @value{op-exclude} or dumping entire filesystems.
+Therefore, @code{tar} supports multiple tapes automatically.
+
+Use @value{op-multi-volume} on the command line, and then @code{tar} will,
+when it reaches the end of the tape, prompt for another tape, and
+continue the archive. Each tape will have an independent archive, and
+can be read without needing the other. (As an exception to this, the
+file that @code{tar} was archiving when it ran out of tape will usually
+be split between the two archives; in this case you need to extract from
+the first archive, using @value{op-multi-volume}, and then put in the
+second tape when prompted, so @code{tar} can restore both halves of the
+file.)
+
+GNU @code{tar} multi-volume archives do not use a truly portable format.
+You need GNU @code{tar} at both end to process them properly.
+
+When prompting for a new tape, @code{tar} accepts any of the following
+responses:
+
+@table @kbd
+@item ?
+Request @code{tar} to explain possible responses
+@item q
+Request @code{tar} to exit immediately.
+@item n @var{file name}
+Request @code{tar} to write the next volume on the file @var{file name}.
+@item !
+Request @code{tar} to run a subshell.
+@item y
+Request @code{tar} to begin writing the next volume.
+@end table
-@node Quick Reference, Data Format Details, Media, Top
-@appendix A Quick Reference Guide to @code{tar} Operations and Options
-@c put in proper form for appendix. (unnumbered?)
+(You should only type @samp{y} after you have changed the tape;
+otherwise @code{tar} will write over the volume it just finished.)
+
+If you want more elaborate behavior than this, give @code{tar} the
+@value{op-info-script} option. The file @var{script-name} is expected
+to be a program (or shell script) to be run instead of the normal
+prompting procedure. When the program finishes, @code{tar} will
+immediately begin writing the next volume. The behavior of the
+@samp{n} response to the normal tape-change prompt is not available
+if you use @value{op-info-script}.
+
+The method @code{tar} uses to detect end of tape is not perfect, and
+fails on some operating systems or on some devices. You can use the
+@value{op-tape-length} option if @code{tar} can't detect the end of the
+tape itself. This option selects @value{op-multi-volume} automatically.
+The @var{size} argument should then be the usable size of the tape.
+But for many devices, and floppy disks in particular, this option is
+never required for real, as far as we know.
+
+The volume number used by @code{tar} in its tape-change prompt
+can be changed; if you give the @value{op-volno-file} option, then
+@var{file-of-number} should be an unexisting file to be created, or else,
+a file already containing a decimal number. That number will be used
+as the volume number of the first volume written. When @code{tar} is
+finished, it will rewrite the file with the now-current volume number.
+(This does not change the volume number written on a tape label, as
+per @value{ref-label}, it @emph{only} affects the number used in
+the prompt.)
+
+If you want @code{tar} to cycle through a series of tape drives, then
+you can use the @samp{n} response to the tape-change prompt. This is
+error prone, however, and doesn't work at all with @value{op-info-script}.
+Therefore, if you give @code{tar} multiple @value{op-file} options, then
+the specified files will be used, in sequence, as the successive volumes
+of the archive. Only when the first one in the sequence needs to be
+used again will @code{tar} prompt for a tape change (or run the info
+script).
+
+Multi-volume archives
+
+With @value{op-multi-volume}, @code{tar} will not abort when it cannot
+read or write any more data. Instead, it will ask you to prepare a new
+volume. If the archive is on a magnetic tape, you should change tapes
+now; if the archive is on a floppy disk, you should change disks, etc.
+
+Each volume of a multi-volume archive is an independent @code{tar}
+archive, complete in itself. For example, you can list or extract any
+volume alone; just don't specify @value{op-multi-volume}. However, if one
+file in the archive is split across volumes, the only way to extract
+it successfully is with a multi-volume extract command @samp{--extract
+--multi-volume} (@samp{-xM}) starting on or before the volume where
+the file begins.
+
+For example, let's presume someone has two tape drives on a system
+named @file{/dev/tape0} and @file{/dev/tape1}. For having GNU
+@code{tar} to switch to the second drive when it needs to write the
+second tape, and then back to the first tape, etc., just do either of:
+
+@smallexample
+$ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}}
+$ @kbd{tar cMff /dev/tape0 /dev/tape1 @var{files}}
+@end smallexample
@menu
-* Operations:: A Table of Operations
-* Options:: Table of Options
+* Multi-Volume Archives:: Archives Longer than One Tape or Disk
+* Tape Files:: Tape Files
@end menu
-@node Operations, Options, Quick Reference, Quick Reference
-@appendixsec A Table of Operations
-@c add xrefs, note synonyms
-
-The operation argument to @code{tar} specifies which action you want to
-take.
-
-@table @samp
-@item -A
-Adds copies of an archive or archives to the end of another archive.
-
-@item -c
-Creates a new archive.
-
-@item -d
-Compares files in the archive with their counterparts in the file
-system, and reports differences in file size, mode, owner,
-modification date and contents.
-
-@item -r
-Adds files to the end of the archive.
-
-@item -t
-Prints a list of the contents of the archive.
-
-@item -x
-Reads files from the archive and writes them into the active file
-system.
-
-@item -u
-Adds files to the end of the archive, but only if they are newer than
-their counterparts already in the archive, or if they do not already
-exist in the archive.
-
-@item +add-archive
-Adds copies of an archive or archives to the end of another archive.
-
-@item +add-file
-Adds files to the end of the archive.
-
-@item +append
-Adds files to the end of the archive.
-
-@item +catenate
-Adds copies of an archive or archives to the end of another archive.
+@node Multi-Volume Archives, Tape Files, Using Multiple Tapes, Using Multiple Tapes
+@subsection Archives Longer than One Tape or Disk
+@cindex Multi-volume archives
+@UNREVISED
-@item +compare
-Compares files in the archive with their counterparts in the file
-system, and reports differences in file size, mode, owner,
-modification date and contents.
+To create an archive that is larger than will fit on a single unit of
+the media, use the @value{op-multi-volume} option in conjunction with
+the @value{op-create} option (@pxref{create}). A
+@dfn{multi-volume} archive can be manipulated like any other archive
+(provided the @value{op-multi-volume} option is specified), but is
+stored on more than one tape or disk.
-@item +concatenate
-Adds copies of an archive or archives to the end of another archive.
+When you specify @value{op-multi-volume}, @code{tar} does not report an
+error when it comes to the end of an archive volume (when reading), or
+the end of the media (when writing). Instead, it prompts you to load
+a new storage volume. If the archive is on a magnetic tape, you
+should change tapes when you see the prompt; if the archive is on a
+floppy disk, you should change disks; etc.
-@item +create
-Creates a new archive.
+You can read each individual volume of a multi-volume archive as if it
+were an archive by itself. For example, to list the contents of one
+volume, use @value{op-list}, without @value{op-multi-volume} specified.
+To extract an archive member from one volume (assuming it is described
+that volume), use @value{op-extract}, again without
+@value{op-multi-volume}.
-@item +delete
-Deletes files from the archive. All versions of the files are deleted.
+If an archive member is split across volumes (ie. its entry begins on
+one volume of the media and ends on another), you need to specify
+@value{op-multi-volume} to extract it successfully. In this case, you
+should load the volume where the archive member starts, and use
+@samp{tar --extract --multi-volume}---@code{tar} will prompt for later
+volumes as it needs them. @xref{extracting archives}, for more
+information about extracting archives.
-@item +diff
-Compares files in the archive with their counterparts in the file
-system, and reports differences in file size, mode, owner,
-modification date and contents.
+@value{op-info-script} is like @value{op-multi-volume}, except that
+@code{tar} does not prompt you directly to change media volumes when
+a volume is full---instead, @code{tar} runs commands you have stored
+in @var{script-name}. For example, this option can be used to eject
+cassettes, or to broadcast messages such as @samp{Someone please come
+change my tape} when performing unattended backups. When @var{script-name}
+is done, @code{tar} will assume that the media has been changed.
-@item +extract
-Reads files from the archive and writes them into the active file
-system.
+Multi-volume archives can be modified like any other archive. To add
+files to a multi-volume archive, you need to only mount the last
+volume of the archive media (and new volumes, if needed). For all
+other operations, you need to use the entire archive.
-@item +get
-Reads files from the archive and writes them into the active file
-system.
+If a multi-volume archive was labeled using @value{op-label}
+(@value{pxref-label}) when it was created, @code{tar} will not
+automatically label volumes which are added later. To label subsequent
+volumes, specify @value{op-label} again in conjunction with the
+@value{op-append}, @value{op-update} or @value{op-concatenate} operation.
-@item +help
-Prints a list of @code{tar} operations and options.
+@cindex Labelling multi-volume archives
+@FIXME{example}
-@item +list
-Prints a list of the contents of the archive.
+@FIXME{There should be a sample program here, including an exit
+before end. Is the exit status even checked in tar? :-(}
-@item +update
-Adds files to the end of the archive, but only if they are newer than
-their counterparts already in the archive, or if they do not already
-exist in the archive.
+@table @kbd
+@item --multi-volume
+@itemx -M
+Creates a multi-volume archive, when used in conjunction with
+@value{op-create}. To perform any other operation on a multi-volume
+archive, specify @value{op-multi-volume} in conjunction with that
+operation.
-@item +version
-Prints the version number of the @code{tar} program to the standard
-error.
+@item --info-script=@var{program-file}
+@itemx -F @var{program-file}
+Creates a multi-volume archive via a script. Used in conjunction with
+@value{op-create}.
@end table
-@node Options, , Operations, Quick Reference
-@appendixsec Table of Options
-
-Options change the way @code{tar} performs an operation.
-
-@table @samp
-@item +absolute-paths
-WILL BE INPUT WHEN QUESTION IS RESOLVED
-
-@item +after-date=@var{date}
-Limit the operation to files changed after the given date.
-@xref{File Exclusion}.
-
-@item +block-size=@var{number}
-Specify the blocking factor of an archive. @xref{Blocking Factor}.
-
-@item +compress
-Specify a compressed archive. @xref{Compressed Archives}.
-
-@item +compress-block.
-Create a whole block sized compressed archive. @xref{Compressed Archives}.
-
-@item +confirmation
-Solicit confirmation for each file. @xref{Interactive Operation}
-<<< +selective should be a synonym.
-
-@item +dereference
-Treat a symbolic link as an alternate name for the file the link
-points to. @xref{Symbolic Links}.
-
-@item +directory=@file{directory}
-Change the working directory. @xref{Changing Working Directory}.
-
-@item +exclude=@var{pattern}
-Exclude files which match the regular expression @var{pattern}.
-@xref{File Exclusion}.
-
-@item +exclude-from=@file{file}
-Exclude files which match any of the regular expressions listed in
-the file @file{file}. @xref{File Exclusion}.
-
-@item +file=@var{archive-name}
-Name the archive. @xref{Archive Name}).
-
-@item +files-from=@file{file}
-Read file-name arguments from a file on the file system.
-@xref{File Name Lists}.
-
-@item +ignore-umask
-Set modes of extracted files to those recorded in the archive.
-@xref{File Writing Options}.
-
-@item +ignore-zeros
-Ignore end-of-archive entries. @xref{Archive Reading Options}.
-<<< this should be changed to +ignore-end
-
-@item +listed-incremental=@var{file-name} (-g)
-Take a file name argument always. If the file doesn't exist, run a level
-zero dump, creating the file. If the file exists, uses that file to see
-what has changed.
-
-@item +incremental (-G)
-@c <<<look it up>>>
-
-@item +tape-length=@var{n} (-L)
-@c <<<alternate way of doing multi archive, will go to that length and
-@c prompts for new tape, automatically turns on multi-volume. >>>
-@c <<< this needs to be written into main body as well -ringo
-
-@item +info-script=@var{program-file}
-Create a multi-volume archive via a script. @xref{Multi-Volume Archives}.
-
-@item +interactive
-Ask for confirmation before performing any operation on a file or
-archive member.
+Beware that there is @emph{no} real standard about the proper way, for a
+@code{tar} archive, to span volume boundaries. If you have a multi-volume
+created by some vendor's @code{tar}, there is almost no chance you could
+read all the volumes with GNU @code{tar}. The converse is also true:
+you may not expect multi-volume archives created by GNU @code{tar} to
+be fully recovered by vendor's @code{tar}. Since there is little chance
+that, in mixed system configurations, some vendor's @code{tar} will work on
+another vendor's machine, and there is a great chance that GNU @code{tar}
+will work on most of them, your best bet is to install GNU @code{tar}
+on all machines between which you know exchange of files is possible.
+
+@node Tape Files, , Multi-Volume Archives, Using Multiple Tapes
+@subsection Tape Files
+@UNREVISED
+
+To give the archive a name which will be recorded in it, use the
+@value{op-label} option. This will write a special block identifying
+@var{volume-label} as the name of the archive to the front of the archive
+which will be displayed when the archive is listed with @value{op-list}.
+If you are creating a multi-volume archive with @value{op-multi-volume}
+(@FIXME-pxref{Using Multiple Tapes}), then the volume label will have
+@samp{Volume @var{nnn}} appended to the name you give, where @var{nnn} is
+the number of the volume of the archive. (If you use the @value{op-label}
+option when reading an archive, it checks to make sure the label on the
+tape matches the one you give. @value{xref-label}.
+
+When @code{tar} writes an archive to tape, it creates a single
+tape file. If multiple archives are written to the same tape, one
+after the other, they each get written as separate tape files. When
+extracting, it is necessary to position the tape at the right place
+before running @code{tar}. To do this, use the @code{mt} command.
+For more information on the @code{mt} command and on the organization
+of tapes into a sequence of tape files, see @ref{mt}.
+
+People seem to often do:
-@item +keep-old-files
-Prevent overwriting during extraction. @xref{File Writing Options}.
-
-@item +label=@var{archive-label}
-Include an archive-label in the archive being created. @xref{Archive
-Label}.
-
-@item +modification-time
-Set the modification time of extracted files to the time they were
-extracted. @xref{File Writing Options}.
-
-@item +multi-volume
-Specify a multi-volume archive. @xref{Multi-Volume Archives}.
-
-@item +newer=@var{date}
-Limit the operation to files changed after the given date.
-@xref{File Exclusion}.
-
-@item +newer-mtime=@var{date}
-Limit the operation to files modified after the given date. @xref{File
-Exclusion}.
-
-@item +old
-Create an old format archive. @xref{Old Style File Information}.
-@c <<< did we agree this should go away as a synonym?
-
-@item +old-archive
-Create an old format archive. @xref{Old Style File Information}.
-
-@item +one-file-system
-Prevent @code{tar} from crossing file system boundaries when
-archiving. @xref{File Exclusion}.
-
-@item +portable
-Create an old format archive. @xref{Old Style File Information}.
-@c <<< was portability, may still need to be changed
-
-@item +preserve-order
-Help process large lists of file-names on machines with small amounts of
-memory. @xref{Archive Reading Options}.
-
-@item +preserve-permission
-Set modes of extracted files to those recorded in the archive.
-@xref{File Writing Options}.
-
-@item +read-full-blocks
-Read an archive with a smaller than specified block size or which
-contains incomplete blocks. @xref{Archive Reading Options}).
-@c should be +partial-blocks (!!!)
-
-@item +record-number
-Print the record number where a message is generated.
-@xref{Additional Information}.
-
-@item +same-order
-Help process large lists of file-names on machines with small amounts of
-memory. @xref{Archive Reading Options}.
-
-@item +same-permission
-Set the modes of extracted files to those recorded in the archive.
-@xref{File Writing Options}.
-
-@item +sparse
-Archive sparse files sparsely. @xref{Sparse Files}.
-
-@item +starting-file=@var{file-name}
-Begin reading in the middle of an archive. @xref{Scarce Disk Space}.
-
-@item +to-stdout
-Write files to the standard output. @xref{File Writing Options}.
-
-@item +uncompress
-Specifdo a compressed archive. @xref{Compressed Archives}.
-
-@item -V @var{archive-label}
-Include an archive-label in the archive being created. @xref{Archive
-Label}.
-@c was +volume
-
-@item +verbose
-Print the names of files or archive members as they are being
-operated on. @xref{Additional Information}.
-
-@item +verify
-Check for discrepancies in the archive immediately after it is
-written. @xref{Write Verification}.
-
-@item -B
-Read an archive with a smaller than specified block size or which
-contains incomplete blocks. @xref{Archive Reading Options}).
-
-@item -K @var{file-name}
-Begin reading in the middle of an archive. @xref{Scarce Disk Space}.
-
-@item -M
-Specify a multi-volume archive. @xref{Multi-Volume Archives}.
-
-@item -N @var{date}
-Limit operation to files changed after the given date. @xref{File Exclusion}.
-
-@item -O
-Write files to the standard output. @xref{File Writing Options}.
-
-@c <<<<- P is absolute paths, add when resolved. -ringo>>>
-
-@item -R
-Print the record number where a message is generated.
-@xref{Additional Information}.
-
-@item -S
-Archive sparse files sparsely. @xref{Sparse Files}.
-
-@item -T @var{file}
-Read file-name arguments from a file on the file system.
-@xref{File Name Lists}.
-
-@item -W
-Check for discrepancies in the archive immediately after it is
-written. @xref{Write Verification}.
-
-@item -Z
-Specify a compressed archive. @xref{Compressed Archives}.
-
-@item -b @var{number}
-Specify the blocking factor of an archive. @xref{Blocking Factor}.
-
-@item -f @var{archive-name}
-Name the archive. @xref{Archive Name}).
-
-@item -h
-Treat a symbolic link as an alternate name for the file the link
-points to. @xref{Symbolic Links}.
-
-@item -i
-Ignore end-of-archive entries. @xref{Archive Reading Options}.
-
-@item -k
-Prevent overwriting during extraction. @xref{File Writing Options}.
-
-@item -l
-Prevent @code{tar} from crossing file system boundaries when
-archiving. @xref{File Exclusion}.
-
-@item -m
-Set the modification time of extracted files to the time they were
-extracted. @xref{File Writing Options}.
-
-@item -o
-Create an old format archive. @xref{Old Style File Information}.
-
-@item -p
-Set the modes of extracted files to those recorded in the archive.
-@xref{File Writing Options}.
-
-@item -s
-Help process large lists of file-names on machines with small amounts of
-memory. @xref{Archive Reading Options}.
-
-@item -v
-Print the names of files or archive members they are being operated
-on. @xref{Additional Information}.
-
-@item -w
-@c <<<see +interactive. WILL BE INPUT WHEN QUESTIONS ARE RESOLVED.>>>
-
-@item -z
-Specify a compressed archive. @xref{Compressed Archives}.
-
-@item -z -z
-Create a whole block sized compressed archive. @xref{Compressed Archives}.
-@c I would rather this were -Z. it is the only double letter short
-@c form.
+@example
+@kbd{--label="@var{some-prefix} `date +@var{some-format}`"}
+@end example
-@item -C @file{directory}
-Change the working directory. @xref{Changing Working Directory}.
+or such, for pushing a common date in all volumes or an archive set.
-@item -F @var{program-file}
-Create a multi-volume archive via a script. @xref{Multi-Volume Archives}.
+@node label, verify, Using Multiple Tapes, Media
+@section Including a Label in the Archive
+@cindex Labeling an archive
+@cindex Labels on the archive media
+@UNREVISED
-@item -X @file{file}
-Exclude files which match any of the regular expressions listed in
-the file @file{file}. @xref{File Exclusion}.
+@table @kbd
+@item -V @var{name}
+@itemx --label=@var{name}
+Create archive with volume name @var{name}.
@end table
-@node Data Format Details, Concept Index, Quick Reference, Top
-@appendix Details of the Archive Data Format
-
-This chapter is based heavily on John Gilmore's @i{tar}(5) manual page
-for the public domain @code{tar} that GNU @code{tar} is based on.
-@c it's been majorly edited since, we may be able to lose this.
-
-The archive media contains a series of records, each of which contains
-512 bytes. Each archive member is represented by a header record,
-which describes the file, followed by zero or more records which
-represent the contents of the file. At the end of the archive file
-there may be a record consisting of a series of binary zeros, as an
-end-of-archive marker. GNU @code{tar} writes a record of zeros at the
-end of an archive, but does not assume that such a record exists when
-reading an archive.
+This option causes @code{tar} to write out a @dfn{volume header} at
+the beginning of the archive. If @value{op-multi-volume} is used, each
+volume of the archive will have a volume header of @samp{@var{name}
+Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the
+next, and so on.
-Records may be grouped into @dfn{blocks} for I/O operations. A block
-of records is written with a single @code{write()} operation. The
-number of records in a block is specified using the @samp{+block-size}
-option. @xref{Blocking Factor}, for more information about specifying
-block size.
+@FIXME{Should the arg to --label be a quoted string?? No.}
-@menu
-* Header Data:: The Distribution of Data in the Header
-* Header Fields:: The Meaning of Header Fields
-* Sparse File Handling:: Fields to Handle Sparse Files
-@end menu
-
-@node Header Data, Header Fields, Data Format Details, Data Format Details
-@appendixsec The Distribution of Data in the Header
-
-The header record is defined in C as follows:
-@c I am taking the following code on faith.
-
-@example
-@r{Standard Archive Format - Standard TAR - USTAR}
-
-#define RECORDSIZE 512
-#define NAMSIZ 100
-#define TUNMLEN 32
-#define TGNMLEN 32
-#define SPARSE_EXT_HDR 21
-#define SPARSE_IN_HDR 4
-
-struct sparse @{
- char offset[12];
- char numbytes[12];
-@};
-
-union record @{
- char charptr[RECORDSIZE];
- struct header @{
- char name[NAMSIZ];
- char mode[8];
- char uid[8];
- char gid[8];
- char size[12];
- char mtime[12];
- char chksum[8];
- char linkflag;
- char linkname[NAMSIZ];
- char magic[8];
- char uname[TUNMLEN];
- char gname[TGNMLEN];
- char devmajor[8];
- char devminor[8];
-
-@r{The following fields were added by gnu and are not used by other}
-@r{versions of @code{tar}}.
- char atime[12];
- char ctime[12];
- char offset[12];
- char longnames[4];
-@r{The next three fields were added by gnu to deal with shrinking down}
-@r{sparse files.}
- struct sparse sp[SPARSE_IN_HDR];
- char isextended;
-@r{This is the number of nulls at the end of the file, if any.}
- char ending_blanks[12];
-
- @} header;
-
- struct extended_header @{
- struct sparse sp[21];
- char isextended;
- @} ext_hdr;
-
-@};
-@c <<< this whole thing needs to be put into better english
-
-@r{The checksum field is filled with this while the checksum is computed.}
-#define CHKBLANKS " " @r{8 blanks, no null}
-
-@r{Inclusion of this field marks an archive as being in standard}
-@r{Posix format (though GNU tar itself is not Posix conforming). GNU}
-@r{tar puts "ustar" in this field if uname and gname are valid.}
-#define TMAGIC "ustar " @r{7 chars and a null}
-
-@r{The magic field is filled with this if this is a GNU format dump entry.}
-#define GNUMAGIC "GNUtar " @r{7 chars and a null}
-
-@r{The linkflag defines the type of file.}
-#define LF_OLDNORMAL '\0' @r{Normal disk file, Unix compatible}
-#define LF_NORMAL '0' @r{Normal disk file}
-#define LF_LINK '1' @r{Link to previously dumped file}
-#define LF_SYMLINK '2' @r{Symbolic link}
-#define LF_CHR '3' @r{Character special file}
-#define LF_BLK '4' @r{Block special file}
-#define LF_DIR '5' @r{Directory}
-#define LF_FIFO '6' @r{FIFO special file}
-#define LF_CONTIG '7' @r{Contiguous file}
-
-@r{hhe following are further link types which were defined later.}
-
-@r{This is a dir entry that contains the names of files that were in}
-@r{the dir at the time the dump was made.}
-#define LF_DUMPDIR 'D'
-
-@r{This is the continuation of a file that began on another volume}
-#define LF_MULTIVOL 'M'
-
-@r{This is for sparse files}
-#define LF_SPARSE 'S'
-
-@r{This file is a tape/volume header. Ignore it on extraction.}
-#define LF_VOLHDR 'V'
-
-@r{These are bits used in the mode field - the values are in octal}
-#define TSUID 04000 @r{Set UID on execution}
-#define TSGID 02000 @r{Set GID on execution}
-#define TSVTX 01000 @r{Save text (sticky bit)}
-
-@r{These are file permissions}
-#define TUREAD 00400 @r{read by owner}
-#define TUWRITE 00200 @r{write by owner}
-#define TUEXEC 00100 @r{execute/search by owner}
-#define TGREAD 00040 @r{read by group}
-#define TGWRITE 00020 @r{write by group}
-#define TGEXEC 00010 @r{execute/search by group}
-#define TOREAD 00004 @r{read by other}
-#define TOWRITE 00002 @r{write by other}
-#define TOEXEC 00001 @r{execute/search by other}
-@end example
-
-
-All characters in headers are 8-bit characters in the local variant of
-ASCII. Each field in the header is contiguous; that is, there is no
-padding in the header format.
-
-Data representing the contents of files is not translated in any way
-and is not constrained to represent characters in any character set.
-@code{tar} does not distinguish between text files and binary files.
+To avoid problems caused by misplaced paper labels on the archive
+media, you can include a @dfn{label} entry---an archive member which
+contains the name of the archive---in the archive itself. Use the
+@value{op-label} option in conjunction with the @value{op-create} operation
+to include a label entry in the archive as it is being created.
-The @code{name}, @code{linkname}, @code{magic}, @code{uname}, and
-@code{gname} fields contain null-terminated character strings. All
-other fields contain zero-filled octal numbers in ASCII. Each numeric
-field of width @var{w} contains @var{w} @minus{} 2 digits, a space, and a
-null, except @code{size} and @code{mtime}, which do not contain the
-trailing null.
-
-@node Header Fields, Sparse File Handling, Header Data, Data Format Details
-@appendixsec The Meaning of Header Fields
-
-The @code{name} field contains the name of the file.
-<<< how big a name before field overflows?
-
-The @code{mode} field contains nine bits which specify file
-permissions, and three bits which specify the Set UID, Set GID, and
-Save Text (``stick'') modes. Values for these bits are defined above.
-@xref{File Writing Options}, for information on how file permissions
-and modes are used by @code{tar}.
-
-The @code{uid} and @code{gid} fields contain the numeric user and
-group IDs of the file owners. If the operating system does not
-support numeric user or group IDs, these fields should be ignored.
-@c but are they?
-
-The @code{size} field contains the size of the file in bytes; this
-field contains a zero if the header describes a link to a file.
-
-The @code{mtime} field contains the modification time of the file.
-This is the ASCII representation of the octal value of the last time
-the file was modified, represented as an integer number of seconds
-since January 1, 1970, 00:00 Coordinated Universal Time.
-@xref{File Writing Options}, for a description of how @code{tar} uses
-this information.
-
-The @code{chksum} field contains the ASCII representation of the octal
-value of the simple sum of all bytes in the header record. To
-generate this sum, each 8-bit byte in the header is added to an
-unsigned integer, which has been initialized to zero. The precision
-of the integer is seventeen bits. When calculating the checksum, the
-@code{chksum} field itself is treated as blank.
-
-The @code{atime} and @code{ctime} fields are used when making
-incremental backups; they store, respectively, the file's access time
-and last inode-change time.
+If you create an archive using both @value{op-label} and
+@value{op-multi-volume}, each volume of the archive will have an
+archive label of the form @samp{@var{archive-label} Volume @var{n}},
+where @var{n} is 1 for the first volume, 2 for the next, and so on.
+@FIXME-xref{Multi-Volume Archives}, for information on creating multiple
+volume archives.
-The value in the @code{offset} field is used when making a
-multi-volume archive. The offset is number of bytes into the file
-that we need to go to pick up where we left off in the previous
-volume, i.e the location that a continued file is continued from.
+If you list or extract an archive using @value{op-label}, @code{tar} will
+print an error if the archive label doesn't match the @var{archive-label}
+specified, and will then not list nor extract the archive. In those cases,
+@var{archive-label} argument is interpreted as a globbing-style pattern
+which must match the actual magnetic volume label. @xref{exclude}, for
+a precise description of how match is attempted@footnote{Previous versions
+of @code{tar} used full regular expression matching, or before that, only
+exact string matching, instead of wildcard matchers. We decided for the
+sake of simplicity to use a uniform matching device through @code{tar}.}.
+If the switch @value{op-multi-volume} is being used, the volume label
+matcher will also suffix @var{archive-label} by @w{@samp{ Volume [1-9]*}}
+if the initial match fails, before giving up. Since the volume numbering
+is automatically added in labels at creation time, it sounded logical to
+equally help the user taking care of it when the archive is being read.
+
+The @value{op-label} was once called @samp{--volume}, but is not available
+under that name anymore.
-The @code{longnames} field supports a feature that is not yet
-implemented. This field should be empty.
+To find out an archive's label entry (or to find out if an archive has
+a label at all), use @samp{tar --list --verbose}. @code{tar} will print the
+label first, and then print archive member information, as in the
+example below:
-The @code{magic} field indicates that this archive was output in the
-P1003 archive format. If this field contains @code{TMAGIC}, the
-@code{uname} and @code{gname} fields will contain the ASCII
-representation of the owner and group of the file respectively. If
-found, the user and group IDs are used rather than the values in the
-@code{uid} and @code{gid} fields.
+@example
+$ @kbd{tar --verbose --list --file=iamanarchive}
+V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
+-rw-rw-rw- ringo user 40 1990-05-21 13:30 iamafilename
+@end example
-The @code{sp} field is used to archive sparse files efficiently.
-@xref{Sparse File Handling}, for a description of this field, and
-other fields it may imply.
+@table @kbd
+@item --label=@var{archive-label}
+@itemx -V @var{archive-label}
+Includes an @dfn{archive-label} at the beginning of the archive when
+the archive is being created, when used in conjunction with the
+@value{op-create} option. Checks to make sure the archive label
+matches the one specified (when used in conjunction with the
+@value{op-extract} option.
+@end table
-The @code{typeflag} field specifies the file's type. If a particular
-implementation does not recognize or permit the specified type,
-@code{tar} extracts the file as if it were a regular file, and reports
-the discrepancy on the standard error. @xref{File Types}. @xref{GNU
-File Types}.
+To get a common information on all tapes of a series, use the
+@value{op-label} option. For having this information different in each
+series created through a single script used on a regular basis, just
+manage to get some date string as part of the label. For example:
-@menu
-* File Types:: File Types
-* GNU File Types:: Additional File Types Supported by GNU
-@end menu
+@example
+$ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"}
+$ @kbd{tar --create --file=/dev/tape --multi-volume \
+ --volume="Daily backup for `date +%Y-%m-%d`"}
+@end example
-@node File Types, GNU File Types, Header Fields, Header Fields
-@appendixsubsec File Types
+Also note that each label has its own date and time, which corresponds
+to when GNU @code{tar} initially attempted to write it, often soon
+after the operator launches @code{tar} or types the carriage return
+telling that the next tape is ready. Comparing date labels does give
+an idea of tape throughput only if the delays for rewinding tapes
+and the operator switching them were negligible, which is ususally
+not the case.
-The following flags are used to describe file types:
+@FIXME{was --volume}
-@table @code
-@item LF_NORMAL
-@itemx LF_OLDNORMAL
-Indicates a regular file. In order to be compatible with older
-versions of @code{tar}, a @code{typeflag} value of @code{LF_OLDNORMAL}
-should be silently recognized as a regular file. New archives should
-be created using @code{LF_NORMAL} for regular files. For backward
-compatibility, @code{tar} treats a regular file whose name ends with a
-slash as a directory.
-
-@item LF_LINK
-Indicates a link to another file, of any type, which has been
-previously archived. @code{tar} identifies linked files in Unix by
-matching device and inode numbers. The linked-to name is specified in
-the @code{linkname} field with a trailing null.
-
-@item LF_SYMLINK
-Indicates a symbolic link to another file. The linked-to
-name is specified in the @code{linkname} field with a trailing null.
-@xref{File Writing Options}, for information on archiving files
-referenced by a symbolic link.
-
-@item LF_CHR
-@itemx LF_BLK
-Indicate character special files and block special files,
-respectively. In this case the @code{devmajor} and @code{devminor}
-fields will contain the major and minor device numbers. Operating
-systems may map the device specifications to their own local
-specification, or may ignore the entry.
-
-@item LF_DIR
-Indicates a directory or sub-directory. The directory name in the
-@code{name} field should end with a slash. On systems where disk
-allocation is performed on a directory basis, the @code{size} field
-will contain the maximum number of bytes (which may be rounded to the
-nearest disk block allocation unit) that the directory can hold. A
-@code{size} field of zero indicates no size limitations. Systems that
-do not support size limiting in this manner should ignore the
-@code{size} field.
+@node verify, Write Protection, label, Media
+@section Verifying Data as It is Stored
+@cindex Verifying a write operation
+@cindex Double-checking a write operation
-@item LF_FIFO
-Indicates a FIFO special file. Note that archiving a FIFO file
-archives the existence of the file and not its contents.
-
-@item LF_CONTIG
-Indicates a contiguous file. Contiguous files are the same as normal
-files except that, in operating systems that support it, all the
-files' disk space is allocated contiguously. Operating systems which
-do not allow contiguous allocation should silently treat this type as
-a normal file.
-
-@item 'A' @dots{}
-@itemx 'Z'
-These are reserved for custom implementations. Some of these are used
-in the GNU modified format, which is described below. @xref{GNU File
-Types}.
+@table @kbd
+@item -W
+@itemx --verify
+Attempt to verify the archive after writing.
@end table
-Certain other flag values are reserved for specification in future
-revisions of the P1003 standard, and should not be used by any
-@code{tar} program.
-
-@node GNU File Types, , File Types, Header Fields
-@appendixsubsec Additional File Types Supported by GNU
-
-GNU @code{tar} uses additional file types to describe new types of
-files in an archive. These are listed below.
-
-@table @code
-@item LF_DUMPDIR
-@itemx 'D'
-Indicates a directory and a list of files created by the
-@samp{+incremental} option. The @code{size} field gives the total
-size of the associated list of files. Each file name is preceded by
-either a @code{'Y'} (the file should be in this archive) or an
-@code{'N'} (the file is a directory, or is not stored in the archive).
-Each file name is terminated by a null. There is an additional null
-after the last file name.
-
-@item LF_MULTIVOL
-@itemx 'M'
-Indicates a file continued from another volume of a multi-volume
-archive (@pxref{Multi-Volume Archives}). The original type of the file is not
-given here. The @code{size} field gives the maximum size of this
-piece of the file (assuming the volume does not end before the file is
-written out). The @code{offset} field gives the offset from the
-beginning of the file where this part of the file begins. Thus
-@code{size} plus @code{offset} should equal the original size of the
-file.
-
-@item LF_SPARSE
-@itemx 'S'
-Indicates a sparse file. @xref{Sparse Files}. @xref{Sparse File
-Handling}.
-
-@item LF_VOLHDR
-@itemx 'V'
-Marks an archive label that was created using the @samp{+label} option
-when the archive was created (@pxref{Archive Label}. The @code{name}
-field contains the argument to the option. The @code{size} field is
-zero. Only the first file in each volume of an archive should have
-this type.
-@end table
+This option causes @code{tar} to verify the archive after writing it.
+Each volume is checked after it is written, and any discrepancies
+are recorded on the standard error output.
-@node Sparse File Handling, , Header Fields, Data Format Details
-@appendixsec Fields to Handle Sparse Files
+Verification requires that the archive be on a back-space-able medium.
+This means pipes, some cartridge tape drives, and some other devices
+cannot be verified.
-The following header information was added to deal with sparse files
-(@pxref{Sparse Files}):
+You can insure the accuracy of an archive by comparing files in the
+system with archive members. @code{tar} can compare an archive to the
+file system as the archive is being written, to verify a write
+operation, or can compare a previously written archive, to insure that
+it is up to date.
-@c TALK TO MIB
-The @code{sp} field (fields? something else?) is an array of
-@code{struct sparse}. Each @code{struct sparse} contains two
-12-character strings, which represent the offset into the file and the
-number of bytes to be written at that offset. The offset is absolute,
-and not relative to the offset in preceding array elements.
+To check for discrepancies in an archive immediately after it is
+written, use the @value{op-verify} option in conjunction with
+the @value{op-create} operation. When this option is
+specified, @code{tar} checks archive members against their counterparts
+in the file system, and reports discrepancies on the standard error. In
+multi-volume archives, each volume is verified after it is written,
+before the next volume is written.
-The header can contain four of these @code{struct sparse}; if more are
-needed, they are not stored in the header, instead, the flag
-@code{isextended} is set and the next record is an
-@code{extended_header}.
-@c @code{extended_header} or @dfn{extended_header} ??? the next
-@c record after the header, or in the middle of it.
+To verify an archive, you must be able to read it from before the end
+of the last written entry. This option is useful for detecting data
+errors on some tapes. Archives written to pipes, some cartridge tape
+drives, and some other devices cannot be verified.
-The @code{isextended} flag is only set for sparse files, and then only
-if extended header records are needed when archiving the file.
+One can explicitely compare an already made archive with the file system
+by using the @value{op-compare} option, instead of using the more automatic
+@value{op-verify} option. @value{xref-compare}.
+
+Note that these two options have a slightly different intent. The
+@value{op-compare} option how identical are the logical contents of some
+archive with what is on your disks, while the @value{op-verify} option is
+really for checking if the physical contents agree and if the recording
+media itself is of dependable quality. So, for the @value{op-verify}
+operation, @code{tar} tries to defeat all in-memory cache pertaining to
+the archive, while it lets the speed optimization undisturbed for the
+@value{op-compare} option. If you nevertheless use @value{op-compare} for
+media verification, you may have to defeat the in-memory cache yourself,
+maybe by opening and reclosing the door latch of your recording unit,
+forcing some doubt in your operating system about the fact this is really
+the same volume as the one just written or read.
+
+The @value{op-verify} option would not be necessary if drivers were indeed
+able to detect dependably all write failures. This sometimes require many
+magnetic heads, some able to read after the writes occurred. One would
+not say that drivers unable to detect all cases are necessarily flawed,
+as long as programming is concerned.
+
+@node Write Protection, , verify, Media
+@section Write Protection
-Each extended header record can contain an array of 21 sparse
-structures, as well as another @code{isextended} flag. There is no
-limit (except that implied by the archive media) on the number of
-extended header records that can be used to describe a sparse file.
+Almost all tapes and diskettes, and in a few rare cases, even disks can
+be @dfn{write protected}, to protect data on them from being changed.
+Once an archive is written, you should write protect the media to prevent
+the archive from being accidently overwritten or deleted. (This will
+protect the archive from being changed with a tape or floppy drive---it
+will not protect it from magnet fields or other physical hazards).
-@c so is @code{extended_header} the right way to write this?
+The write protection device itself is usually an integral part of the
+physical media, and can be a two position (write enabled/write
+disabled) switch, a notch which can be popped out or covered, a ring
+which can be removed from the center of a tape reel, or some other
+changeable feature.
-@node Concept Index, , Data Format Details, Top
-@unnumbered Concept Index
+@node Index, , Media, Top
+@unnumbered Index
@printindex cp
@contents
@bye
-
+@c Local variables:
+@c texinfo-column-for-description: 32
+@c End:
projects / chaz / tar / blobdiff