@smallbook
@c %**end of header
+@c Maintenance notes:
+@c 1. Pay attention to @FIXME{}s and @UNREVISED{}s
+@c 2. Before creating final variant:
+@c 2.1. Run `make check-options' to make sure all options are properly
+@c documented;
+@c 2.2. Run `make master-menu' (see comment before the master menu).
+
@include rendition.texi
@include value.texi
+@defcodeindex op
+
@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
-
@copying
This manual is for @acronym{GNU} @command{tar} (version
from archives.
Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001,
-2003, 2004 Free Software Foundation, Inc.
+2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
-any later version published by the Free Software Foundation; with the
-Invariant Sections being "GNU General Public License", with the
-Front-Cover Texts being ``A GNU Manual,'' and with the Back-Cover Texts
-as in (a) below. A copy of the license is included in the section
-entitled "GNU Free Documentation License".
-
-(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
-this GNU Manual. Buying copies from GNU Press supports the FSF in
-developing GNU and promoting software freedom.''
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
+and with the Back-Cover Texts as in (a) below. A copy of the license
+is included in the section entitled "GNU Free Documentation License".
+
+(a) The FSF's Back-Cover Text is: ``You have the freedom to
+copy and modify this GNU manual. Buying copies from the FSF
+supports it in developing GNU and promoting software freedom.''
@end quotation
@end copying
document. The rest of the menu lists all the lower level nodes.
@end ifnottex
-@c The master menu, created with texinfo-master-menu, goes here.
-@c (However, getdate.texi's menu is interpolated by hand.)
+@c The master menu goes here.
+@c
+@c NOTE: To update it from within Emacs, make sure mastermenu.el is
+@c loaded and run texinfo-master-menu.
+@c To update it from the command line, run
+@c
+@c make master-menu
@menu
* Introduction::
Appendices
* Changes::
+* Configuring Help Summary::
+* Fixing Snapshot Files::
+* Tar Internals::
* Genfile::
-* Snapshot Files::
* Free Software Needs Free Documentation::
* Copying This Manual::
* Index of Command Line Options::
* extracting archives::
* extracting files::
* extract dir::
+* extracting untrusted archives::
* failing commands::
Invoking @GNUTAR{}
* help::
* defaults::
* verbose::
+* checkpoints::
* interactive::
The Three Option Styles
-* Mnemonic Options:: Mnemonic Option Style
+* Long Options:: Long Option Style
* Short Options:: Short Option Style
* Old Options:: Old Option Style
* Mixing:: Mixing Option Styles
Options Used by @option{--create}
+* override:: Overriding File Metadata.
* Ignore Failed Read::
Options Used by @option{--extract}
* Recursive Unlink::
* Data Modification Times::
* Setting Access Permissions::
+* Directory Modification Times and Permissions::
* Writing to Standard Output::
+* Writing to an External Program::
* remove files::
Coping with Scarce Resources
* Selecting Archive Members::
* files:: Reading Names from a File
* exclude:: Excluding Some Files
-* Wildcards::
+* wildcards:: Wildcards Patterns and Matching
+* quoting styles:: Ways of Quoting Special Characters in Names
+* transform:: Modifying File and Member Names
* after:: Operating Only on New Files
* recurse:: Descending into Directories
* one:: Crossing File System Boundaries
Excluding Some Files
-* controlling pattern-matching with exclude::
* problems with exclude::
+Wildcards Patterns and Matching
+
+* controlling pattern-matching::
+
Crossing File System Boundaries
* directory:: Changing Directory
* General date syntax:: Common rules.
* Calendar date items:: 19 Dec 1994.
* Time of day items:: 9:20pm.
-* Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}, ...
+* Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
* Day of week items:: Monday and others.
* Relative items in date strings:: next tuesday, 2 years ago.
* Pure numbers in date strings:: 19931219, 1440.
* Seconds since the Epoch:: @@1078100502.
+* Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
* Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
Controlling the Archive Format
-* Portability:: Making @command{tar} Archives More Portable
* Compression:: Using Less Space through Compression
* Attributes:: Handling File Attributes
-* Standard:: The Standard Format
-* Extensions:: @acronym{GNU} Extensions to the Archive Format
+* Portability:: Making @command{tar} Archives More Portable
* cpio:: Comparison of @command{tar} and @command{cpio}
+Using Less Space through Compression
+
+* gzip:: Creating and Reading Compressed Archives
+* sparse:: Archiving Sparse Files
+
Making @command{tar} Archives More Portable
* Portable Names:: Portable Names
* dereference:: Symbolic Links
+* hard links:: Hard Links
* old:: Old V7 Archives
+* ustar:: Ustar Archives
+* gnu:: GNU and old GNU format archives.
* posix:: @acronym{POSIX} archives
* Checksumming:: Checksumming Problems
* Large or Negative Values:: Large files, negative time stamps, etc.
+* Other Tars:: How to Extract GNU-Specific Data Using
+ Other @command{tar} Implementations
-Using Less Space through Compression
+@GNUTAR{} and @acronym{POSIX} @command{tar}
-* gzip:: Creating and Reading Compressed Archives
-* sparse:: Archiving Sparse Files
+* PAX keywords:: Controlling Extended Header Keywords.
+
+How to Extract GNU-Specific Data Using Other @command{tar} Implementations
+
+* Split Recovery:: Members Split Between Volumes
+* Sparse Recovery:: Sparse Members
Tapes and Other Archive Media
* Tape Files:: Tape Files
* Tarcat:: Concatenate Volumes into a Single Archive
-GNU tar internals and development
-* Genfile::
+Tar Internals
+
+* Standard:: Basic Tar Format
+* Extensions:: @acronym{GNU} Extensions to the Archive Format
+* Sparse Formats:: Storing Sparse Files
* Snapshot Files::
+* Dumpdir::
+
+Storing Sparse Files
+
+* Old GNU Format::
+* PAX 0:: PAX Format, Versions 0.0 and 0.1
+* PAX 1:: PAX Format, Version 1.0
+
+Genfile
+
+* Generate Mode:: File Generation Mode.
+* Status Mode:: File Status Mode.
+* Exec Mode:: Synchronous Execution mode.
Copying This Manual
-* Free Software Needs Free Documentation::
* GNU Free Documentation License:: License for copying this manual
@end detailmenu
The third chapter presents the remaining five operations, and
information about using @command{tar} options and option syntax.
-@FIXME{this sounds more like a @acronym{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.
+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 @acronym{GNU} manuals, and is mostly self-contained.
direct its output to available devices, files, or other programs (using
pipes). @command{tar} may even access remote devices or files (as archives).
-@FIXME{the following table entries need a bit of work..}
-
You can use @command{tar} archives in many ways. We want to stress a few
of them: storage, backup, and transportation.
+@FIXME{the following table entries need a bit of work.}
@table @asis
@item Storage
Often, @command{tar} archives are used to store related files for
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.}
+1.12. The book for versions from 1.14 up to @value{VERSION} were edited
+by the current maintainer, Sergey Poznyakoff.
For version 1.12, Daniel Hagerty contributed a great deal of technical
consulting. In particular, he is the primary author of @ref{Backups}.
file system. 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, and the
-differences between relative and absolute path names. @FIXME{and what
+input, what various definitions of the term @samp{argument} mean, and the
+differences between relative and absolute file names. @FIXME{and what
else?}
@item
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 @command{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
+directory to practice @command{tar} commands in. When we show file names,
+we will assume that those names are relative to your home directory.
+For example, my home directory is @file{/home/fsf/melissa}. All of
+my examples are in a subdirectory of the directory named by that file
name; the subdirectory is called @file{practice}.
@item
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 @GNUTAR{} for compatibility with Unix
+corresponding abbreviations. We will indicate those abbreviations
+appropriately to get you used to seeing them. (Note that the ``old
+style'' option forms exist in @GNUTAR{} for compatibility with Unix
@command{tar}. In this book we present a full discussion of this way
of writing options and operations (@pxref{Old Options}), and we discuss
-the other two styles of writing options (@xref{Mnemonic Options}, and
+the other two styles of writing options (@xref{Long Options}, and
@pxref{Short Options}).
In the examples and in the text of this tutorial, we usually use the
two different ways. People sometimes refer to @command{tar} ``commands''.
A @command{tar} @dfn{command} is the entire command line of user input
which tells @command{tar} what to do --- including the operation, options,
-and any arguments (file names, pipes, other commands, etc). However,
+and any arguments (file names, pipes, other commands, etc.). However,
you will also sometimes hear the term ``the @command{tar} command''. When
the word ``command'' is used specifically like this, a person is usually
referring to the @command{tar} @emph{operation}, not the whole line.
@unnumberedsubsec The @option{--file} Option
@table @option
-@opindex file, tutorial
+@xopindex{file, tutorial}
@item --file=@var{archive-name}
@itemx -f @var{archive-name}
Specify the name of an archive file.
--show-defaults}, @pxref{defaults}). If there is no tape drive
attached, or the default is not meaningful, then @command{tar} will
print an error message. The error message might look roughly like one
-of the following:
+of the following:
@smallexample
tar: can't open /dev/rmt8 : No such device or address
@unnumberedsubsec The @option{--verbose} Option
@table @option
-@opindex verbose, introduced
+@xopindex{verbose, introduced}
@item --verbose
@itemx -v
Show the files being worked on as @command{tar} is running.
clear, and we will give many examples both using and not using
@option{--verbose} to show the differences.
-Sometimes, a single instance of @option{--verbose} on the command line
-will show a full, @samp{ls} style listing of an archive or files,
-giving sizes, owners, and similar information. @FIXME{Describe the
-exact output format, e.g., how hard links are displayed.}
-Other times, @option{--verbose} will only show files or members that the particular
-operation is operating on at the time. In the latter case, you can
-use @option{--verbose} twice in a command to get a listing such as that
-in the former case. For example, instead of saying
+Each instance of @option{--verbose} on the command line increases the
+verbosity level by one, so if you need more details on the output,
+specify it twice.
+
+When reading archives (@option{--list}, @option{--extract},
+@option{--diff}), @command{tar} by default prints only the names of
+the members being extracted. Using @option{--verbose} will show a full,
+@command{ls} style member listing.
+
+In contrast, when writing archives (@option{--create}, @option{--append},
+@option{--update}), @command{tar} does not print file names by
+default. So, a single @option{--verbose} option shows the file names
+being added to the archive, while two @option{--verbose} options
+enable the full listing.
+
+For example, to create an archive in verbose mode:
@smallexample
-@kbd{tar -cvf afiles.tar apple angst aspic}
+$ @kbd{tar -cvf afiles.tar apple angst aspic}
+apple
+angst
+aspic
@end smallexample
@noindent
-above, you might say
+Creating the same archive with the verbosity level 2 could give:
@smallexample
-@kbd{tar -cvvf afiles.tar apple angst aspic}
+$ @kbd{tar -cvvf afiles.tar apple angst aspic}
+-rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
+-rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst
+-rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic
@end smallexample
@noindent
Later in the tutorial, we will give examples using @w{@option{--verbose
--verbose}}.
+@anchor{verbose member listing}
+The full output consists of six fields:
+
+@itemize @bullet
+@item File type and permissions in symbolic form.
+These are displayed in the same format as the first column of
+@command{ls -l} output (@pxref{What information is listed,
+format=verbose, Verbose listing, fileutils, GNU file utilities}).
+
+@item Owner name and group separated by a slash character.
+If these data are not available (for example, when listing a @samp{v7} format
+archive), numeric @acronym{ID} values are printed instead.
+
+@item Size of the file, in bytes.
+
+@item File modification date in ISO 8601 format.
+
+@item File modification time.
+
+@item File name.
+If the name contains any special characters (white space, newlines,
+etc.) these are displayed in an unambiguous form using so called
+@dfn{quoting style}. For the detailed discussion of available styles
+and on how to use them, see @ref{quoting styles}.
+
+Depending on the file type, the name can be followed by some
+additional information, described in the following table:
+
+@table @samp
+@item -> @var{link-name}
+The file or archive member is a @dfn{symbolic link} and
+@var{link-name} is the name of file it links to.
+
+@item link to @var{link-name}
+The file or archive member is a @dfn{hard link} and @var{link-name} is
+the name of file it links to.
+
+@item --Long Link--
+The archive member is an old GNU format long link. You will normally
+not encounter this.
+
+@item --Long Name--
+The archive member is an old GNU format long name. You will normally
+not encounter this.
+
+@item --Volume Header--
+The archive member is a GNU @dfn{volume header} (@pxref{Tape Files}).
+
+@item --Continued at byte @var{n}--
+Encountered only at the beginning of a multi-volume archive
+(@pxref{Using Multiple Tapes}). This archive member is a continuation
+from the previous volume. The number @var{n} gives the offset where
+the original file was split.
+
+@item unknown file type @var{c}
+An archive member of unknown type. @var{c} is the type character from
+the archive header. If you encounter such a message, it means that
+either your archive contains proprietary member types @GNUTAR{} is not
+able to handle, or the archive is corrupted.
+@end table
+
+@end itemize
+
+For example, here is an archive listing containing most of the special
+suffixes explained above:
+
+@smallexample
+@group
+V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header--
+-rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at
+byte 32456--
+-rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
+lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple
+-rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues
+hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues
+@end group
+@end smallexample
+
+@smallexample
+@end smallexample
+
@node help tutorial
@unnumberedsubsec Getting Help: Using the @option{--help} Option
Now @command{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
+the full file 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.
@node Creating the archive
@subsection Creating the Archive
-@opindex create, introduced
+@xopindex{create, introduced}
To place the files @file{blues}, @file{folk}, and @file{jazz} into an
archive named @file{collection.tar}, use the following command:
easiest to understand (and we encourage you to do the same when you use
@command{tar}, to avoid errors).
-Note that the part of the command which says,
-@w{@option{--file=collection.tar}} is considered to be @emph{one} argument.
+Note that the sequence
+@option{--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.
(@file{collection.tar}), and @option{--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 @option{--create} operation).
-@FIXME{xref here to the discussion of file name args?}Now that they are
+(they are @dfn{file name arguments} to the @option{--create} operation.
+@xref{Choosing}, for the detailed discussion on these.) Now that they are
in the archive, they are called @emph{archive members}, not files.
(@pxref{Definitions,members}).
@node create verbose
@subsection Running @option{--create} with @option{--verbose}
-@opindex create, using with @option{--verbose}
-@opindex verbose, using with @option{--create}
+@xopindex{create, using with @option{--verbose}}
+@xopindex{verbose, using with @option{--create}}
If you include the @option{--verbose} (@option{-v}) option on the command line,
@command{tar} will list the files it is acting on as it is working. In
verbose mode, the @code{create} example above would appear as:
it. (It makes no sense to put an archive into itself.) @GNUTAR{}
will continue in this case, and create the archive
normally, except for the exclusion of that one file. (@emph{Please
-note:} Other versions of @command{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 @GNUTAR{}.)
- @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.}
+note:} Other implementations of @command{tar} may not be 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
+@GNUTAR{}. In general, it is wise to always place the archive outside
+of the directory being dumped.
@node list
@section How to List Archives
@opindex list
Frequently, you will find yourself wanting to determine exactly what a
-particular archive contains. You can use the @option{--list} (@option{-t}) 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,
+particular archive contains. You can use the @option{--list}
+(@option{-t}) 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,
@smallexample
$ @kbd{tar --list --file=collection.tar}
jazz
@end smallexample
-@FIXME{we hope this will change. if it doesn't, need to show the
-creation of bfiles somewhere above!!! : }
-
@noindent
The archive @file{bfiles.tar} would list as follows:
@end smallexample
@noindent
-Be sure to use a @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option just as with @option{--create} (@option{-c})
-to specify the name of the archive.
+Be sure to use a @option{--file=@var{archive-name}} (@option{-f
+@var{archive-name}}) option just as with @option{--create}
+(@option{-c}) to specify the name of the archive.
-@opindex list, using with @option{--verbose}
-@opindex verbose, using with @option{--list}
-If you use the @option{--verbose} (@option{-v}) option with @option{--list}, then
-@command{tar} will print out a listing reminiscent of @w{@samp{ls -l}},
-showing owner, file size, and so forth.
+@xopindex{list, using with @option{--verbose}}
+@xopindex{verbose, using with @option{--list}}
+If you use the @option{--verbose} (@option{-v}) option with
+@option{--list}, then @command{tar} will print out a listing
+reminiscent of @w{@samp{ls -l}}, showing owner, file size, and so
+forth. This output is described in detail in @ref{verbose member listing}.
-If you had used @option{--verbose} (@option{-v}) mode, the example above would look
-like:
+If you had used @option{--verbose} (@option{-v}) mode, the example
+above would look like:
@smallexample
$ @kbd{tar --list --verbose --file=collection.tar folk}
@table @option
@item --show-stored-names
-Print member (not @emph{file}) names when creating the archive.
+Print member (as opposed to @emph{file}) names when creating the archive.
@end table
@cindex File name arguments, using @option{--list} with
-@opindex list, using with file name arguments
+@xopindex{list, using with file name arguments}
You can specify one or more individual member names as arguments when
using @samp{list}. In this case, @command{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
-@command{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 @command{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 @option{--list} with no file
-names as arguments, @command{tar} will print the names of all the members
-stored in the specified archive.
+Because @command{tar} preserves file names, these must be specified as
+they appear in the archive (i.e., relative to the directory from which
+the archive was created). Therefore, it is essential when specifying
+member names to @command{tar} that you give the exact member names.
+For example, @w{@kbd{tar --list --file=bfiles.tar 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 by default are compared verbatim.
+
+However, @w{@kbd{tar --list --file=bfiles.tar baboon}} would respond
+with @file{baboon}, because this exact member name is in the archive file
+@file{bfiles.tar}. If you are not sure of the exact file name,
+use @dfn{globbing patterns}, for example:
+
+@smallexample
+$ @kbd{tar --list --file=bfiles.tar --wildcards '*b*'}
+@end smallexample
+
+@noindent
+will list all members whose name contains @samp{b}. @xref{wildcards},
+for a detailed discussion of globbing patterns and related
+@command{tar} command line options.
@menu
* list dir::
@option{-x}) operation. As with @option{--create}, specify the name
of the archive with @option{--file} (@option{-f}) option. Extracting
an archive does not modify the archive in any way; you can extract it
-multiple times if you want or need to.
+multiple times if you want or need to.
Using @option{--extract}, you can extract an entire archive, or specific
files. The files can be directories containing other files, or not. As
@subsection Extracting Specific Files
To extract specific archive members, give their exact member names as
-arguments, as printed by @option{--list} (@option{-t}). 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. Its contents will be identical to the
-original file @file{blues} that you deleted.
+arguments, as printed by @option{--list} (@option{-t}). 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. Its
+contents will be identical to the original file @file{blues} that you
+deleted.
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
@noindent
If you list the files in the directory again, you will see that the file
-@file{blues} has been restored, with its original permissions, data modification
-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
+@file{blues} has been restored, with its original permissions, data
+modification times, and owner.@footnote{This is only accidentally
+true, but not in general. Whereas modification times are always
+restored, 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
extracted @samp{blues}. You can confirm this by running @command{tar} with
@option{--list} (@option{-t}).
-@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 @option{--list} (@option{-t})
-(@pxref{list}).
+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}}. If you don't remember the
+exact member names, use @option{--list} (@option{-t}) option
+(@pxref{list}). You can also extract those members that match a
+specific @dfn{globbing pattern}. For example, to extract from
+@file{bfiles.tar} all files that begin with @samp{b}, no matter their
+directory prefix, you could type:
+
+@smallexample
+$ @kbd{tar -x -f bfiles.tar --wildcards --no-anchored 'b*'}
+@end smallexample
+
+@noindent
+Here, @option{--wildcards} instructs @command{tar} to treat
+command line arguments as globbing patterns and @option{--no-anchored}
+informs it that the patterns apply to member names after any @samp{/}
+delimiter. The use of globbing patterns is discussed in detail in
+@xref{wildcards}.
You can extract a file to standard output by combining the above options
with the @option{--to-stdout} (@option{-O}) option (@pxref{Writing to Standard
Output}).
If you give the @option{--verbose} option, then @option{--extract}
-will print the names of the archive members as it extracts them.
+will print the names of the archive members as it extracts them.
@node extract dir
@subsection Extracting Files that are Directories
directory as @file{practice}, you must give @file{practice} as part
of the file names when you extract those files from the archive.
-@FIXME{IMPORTANT! show the final structure, here. figure out what it
-will be.}
-
@node extracting untrusted archives
@subsection Extracting Archives from Untrusted Sources
@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.
+archive. You must use the correct member names, or wildcards, 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.
@node going further
@section Going Further Ahead in this Manual
+@UNREVISED
@FIXME{need to write up a node here about the things that are going to
be in the rest of the manual.}
* help::
* defaults::
* verbose::
+* checkpoints::
* interactive::
@end menu
working directory. @command{tar} will make all file names relative
(by removing leading slashes when archiving or restoring files),
unless you specify otherwise (using the @option{--absolute-names}
-option). @xref{absolute}, for more information about
+option). @xref{absolute}, for more information about
@option{--absolute-names}.
If you give the name of a directory as either a file name or a member
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.
+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 @command{tar} itself may glob on archive members, so when
needed, you must ensure that wildcard characters reach @command{tar} without
clearly diagnosed on @code{stderr}, after a line stating the nature of
the error.
-@GNUTAR{} returns only a few exit statuses. I'm really
-aiming simplicity in that area, for now. If you are not using the
-@option{--compare} @option{--diff}, @option{-d}) 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.
+Possible exit codes of @GNUTAR{} are summarized in the following
+table:
+
+@table @asis
+@item 0
+@samp{Successful termination}.
+
+@item 1
+@samp{Some files differ}. If tar was invoked with @option{--compare}
+(@option{--diff}, @option{-d}) command line option, this means that
+some files in the archive differ from their disk counterparts
+(@pxref{compare}). If tar was given @option{--create},
+@option{--append} or @option{--update} option, this exit code means
+that some files were changed while being archived and so the resulting
+archive does not contain the exact copy of the file set.
+
+@item 2
+@samp{Fatal error}. This means that some fatal, unrecoverable error
+occurred.
+@end table
+
+If @command{tar} has invoked a subprocess and that subprocess exited with a
+nonzero exit code, @command{tar} exits with that code as well.
+This can happen, for example, if @command{tar} was given some
+compression option (@pxref{gzip}) and the external compressor program
+failed. Another example is @command{rmt} failure during backup to the
+remote device (@pxref{Remote Tape Server}).
@node using tar options
@section Using @command{tar} Options
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.
-Some options @emph{may} take an argument (currently, there are
-two such options: @option{--backup} and @option{--occurrence}). Such
-options may have at most long and short forms, they do not have old style
-equivalent. The rules for specifying an argument for such options
-are stricter than those for specifying mandatory arguments. Please,
-pay special attention to them.
+Some options @emph{may} take an argument. Such options may have at
+most long and short forms, they do not have old style equivalent. The
+rules for specifying an argument for such options are stricter than
+those for specifying mandatory arguments. Please, pay special
+attention to them.
@menu
-* Mnemonic Options:: Mnemonic Option Style
+* Long Options:: Long Option Style
* Short Options:: Short Option Style
* Old Options:: Old Option Style
* Mixing:: Mixing Option Styles
@end menu
-@node Mnemonic Options
-@subsection Mnemonic Option Style
-
-@FIXME{have to decide whether or not to replace other occurrences of
-"mnemonic" with "long", or *ugh* vice versa.}
+@node Long Options
+@subsection Long Option Style
-Each option has at least one long (or mnemonic) name starting with two
+Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two
dashes in a row, e.g., @option{--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
+single long option has many different names which are
synonymous, such as @option{--compare} and @option{--diff}. In addition,
long option names can be given unique abbreviations. For example,
@option{--cre} can be used in place of @option{--create} because there is no
-other mnemonic option which begins with @samp{cre}. (One way to find
+other long 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, @command{tar} will tell
you that that abbreviation is ambiguous and you'll know that that
unique abbreviation for the long name of an option you didn't want to
use, you are stuck; @command{tar} will perform the command as ordered.)
-Mnemonic options are meant to be obvious and easy to remember, and their
+Long 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:
gives a fairly good set of hints about what the command does, even
for those not fully acquainted with @command{tar}.
-Mnemonic options which require arguments take those arguments
+Long options which require arguments take those arguments
immediately following the option name. There are two ways of
specifying a mandatory argument. It can be separated from the
option name either by an equal sign, or by any amount of
@node Short Options
@subsection Short Option Style
-Most options also have a short option name. Short options start with
+Most options also have a @dfn{short option} name. Short options start with
a single dash, and are followed by a single character, e.g., @option{-t}
(which is equivalent to @option{--list}). The forms are absolutely
identical in function; they are interchangeable.
@subsection Old Option Style
@UNREVISED
-Like short options, old options are single letters. However, old options
+Like short options, @dfn{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
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 @option{-t}, and consequently, the same as the
-mnemonic option @option{--list}. So for example, the command @w{@samp{tar
+long option @option{--list}. So for example, the command @w{@samp{tar
cv}} specifies the option @option{-v} in addition to the operation @option{-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
@kbd{tar cf archive.tar.gz -z file}
@end smallexample
-@FIXME{still could explain this better; it's redundant:}
-
@cindex option syntax, traditional
As far as we know, all @command{tar} programs, @acronym{GNU} and
non-@acronym{GNU}, support old options. @GNUTAR{}
All three styles may be intermixed in a single @command{tar} command,
so long as the rules for each style are fully
respected@footnote{Before @GNUTAR{} version 1.11.6,
-a bug prevented intermixing old style options with mnemonic options in
+a bug prevented intermixing old style options with long options in
some cases.}. Old style options and either of the modern styles of
options may be mixed within a single @command{tar} command. However,
old style options must be introduced as the first arguments only,
@table @option
-@opindex append, summary
+@opsummary{append}
@item --append
@itemx -r
Appends files to the end of the archive. @xref{append}.
-@opindex catenate, summary
+@opsummary{catenate}
@item --catenate
@itemx -A
Same as @option{--concatenate}. @xref{concatenate}.
-@opindex compare, summary
+@opsummary{compare}
@item --compare
@itemx -d
system, and reports differences in file size, mode, owner,
modification date and contents. @xref{compare}.
-@opindex concatenate, summary
+@opsummary{concatenate}
@item --concatenate
@itemx -A
Appends other @command{tar} archives to the end of the archive.
@xref{concatenate}.
-@opindex create, summary
+@opsummary{create}
@item --create
@itemx -c
Creates a new @command{tar} archive. @xref{create}.
-@opindex delete, summary
+@opsummary{delete}
@item --delete
Deletes members from the archive. Don't try this on a archive on a
tape! @xref{delete}.
-@opindex diff, summary
+@opsummary{diff}
@item --diff
@itemx -d
Same @option{--compare}. @xref{compare}.
-@opindex extract, summary
+@opsummary{extract}
@item --extract
@itemx -x
Extracts members from the archive into the file system. @xref{extract}.
-@opindex get, summary
+@opsummary{get}
@item --get
@itemx -x
Same as @option{--extract}. @xref{extract}.
-@opindex list, summary
+@opsummary{list}
@item --list
@itemx -t
Lists the members in an archive. @xref{list}.
-@opindex update, summary
+@opsummary{update}
@item --update
@itemx -u
-@FIXME{It was: A combination of the @option{--compare} and
-@option{--append} operations. This is not true and rather misleading,
-as @option{--compare} (@option{--diff}, @option{-d}) does a lot more than @option{--update} (@option{-u}) 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}.
+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}.
@end table
@table @option
-@opindex absolute-names, summary
+@opsummary{absolute-names}
@item --absolute-names
@itemx -P
@samp{/} from member names. This option disables that behavior.
@xref{absolute}.
-@opindex after-date, summary
+@opsummary{after-date}
@item --after-date
(See @option{--newer}, @pxref{after})
-@opindex anchored, summary
+@opsummary{anchored}
@item --anchored
-An exclude pattern must match an initial subsequence of the name's components.
-@xref{controlling pattern-matching with exclude}.
+A pattern must match an initial subsequence of the name's components.
+@xref{controlling pattern-matching}.
-@opindex atime-preserve, summary
+@opsummary{atime-preserve}
@item --atime-preserve
@itemx --atime-preserve=replace
@itemx --atime-preserve=system
as support for @option{--atime-preserve=system} improves.
If your operating system does not support
-@option{--atime-preserve=system}, you might be able to preserve access
+@option{--atime-preserve=@-system}, you might be able to preserve access
times reliably by by using the @command{mount} command. For example,
you can mount the file system read-only, or access the file system via
a read-only loopback mount, or use the @samp{noatime} mount option
available on some systems. However, mounting typically requires
superuser privileges and can be a pain to manage.
-@opindex backup, summary
+@opsummary{auto-compress}
+@item --auto-compress
+@itemx -a
+
+During a @option{--create} operation, enables automatic compressed
+format recognition based on the archive suffix. The effect of this
+option is cancelled by @option{--no-auto-compress}. @xref{gzip}.
+
+@opsummary{backup}
@item --backup=@var{backup-type}
Rather than deleting files from the file system, @command{tar} will
back them up using simple or numbered backups, depending upon
@var{backup-type}. @xref{backup}.
-@opindex block-number, summary
+@opsummary{block-number}
@item --block-number
@itemx -R
With this option present, @command{tar} prints error messages for read errors
with the block number in the archive file. @xref{block-number}.
-@opindex blocking-factor, summary
+@opsummary{blocking-factor}
@item --blocking-factor=@var{blocking}
@itemx -b @var{blocking}
Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per
record. @xref{Blocking Factor}.
-@opindex bzip2, summary
+@opsummary{bzip2}
@item --bzip2
@itemx -j
This option tells @command{tar} to read or write archives through
@code{bzip2}. @xref{gzip}.
-@opindex checkpoint, summary
-@item --checkpoint
+@opsummary{check-device}
+@item --check-device
+Check device numbers when creating a list of modified files for
+incremental archiving. This is the default. @xref{device numbers},
+for a detailed description.
-This option directs @command{tar} to print periodic checkpoint messages as it
-reads through the archive. Its intended for when you want a visual
-indication that @command{tar} is still running, but don't want to see
-@option{--verbose} output. @FIXME-xref{}
+@opsummary{checkpoint}
+@item --checkpoint[=@var{number}]
-@opindex check-links, summary
+This option directs @command{tar} to print periodic checkpoint
+messages as it reads through the archive. It is intended for when you
+want a visual indication that @command{tar} is still running, but
+don't want to see @option{--verbose} output. You can also instruct
+@command{tar} to execute a list of actions on each checkpoint, see
+@option{--checklist-action} below. For a detailed description, see
+@ref{checkpoints}.
+
+@opsummary{checkpoint-action}
+@item --checkpoint-action=@var{action}
+Instruct @command{tar} to execute an action upon hitting a
+breakpoint. Here we give only a brief outline. @xref{checkpoints},
+for a complete description.
+
+The @var{action} argument can be one of the following:
+
+@table @asis
+@item bell
+Produce an audible bell on the console.
+
+@item dot
+@itemx .
+Print a single dot on the standard listing stream.
+
+@item echo
+Display a textual message on the standard error, with the status and
+number of the checkpoint. This is the default.
+
+@item echo=@var{string}
+Display @var{string} on the standard error. Before output, the string
+is subject to meta-character expansion.
+
+@item exec=@var{command}
+Execute the given @var{command}.
+
+@item sleep=@var{time}
+Wait for @var{time} seconds.
+
+@item ttyout=@var{string}
+Output @var{string} on the current console (@file{/dev/tty}).
+@end table
+
+Several @option{--checkpoint-action} options can be specified. The
+supplied actions will be executed in order of their appearance in the
+command line.
+
+Using @option{--checkpoint-action} without @option{--checkpoint}
+assumes default checkpoint frequency of one checkpoint per 10 records.
+
+@opsummary{check-links}
@item --check-links
@itemx -l
If this option was given, @command{tar} will check the number of links
dumped for each processed file. If this number does not match the
total number of hard links for the file, a warning message will be
-output.
+output @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
+synonym for @option{--one-file-system}. The current semantics, which
+complies to UNIX98, was introduced with version
+1.15.91. @xref{Changes}, for more information.}.
-Future versions will take @option{-l} as a short version of
-@option{--check-links}. However, current release still retains the old
-semantics for @option{-l}.
-
-@xref{Changes}, for more information.
+@xref{hard links}.
-@opindex compress, summary
-@opindex uncompress, summary
+@opsummary{compress}
+@opsummary{uncompress}
@item --compress
@itemx --uncompress
@itemx -Z
writing the archive. This allows you to directly act on archives
while saving space. @xref{gzip}.
-@opindex confirmation, summary
+@opsummary{confirmation}
@item --confirmation
(See @option{--interactive}.) @xref{interactive}.
-@opindex dereference, summary
+@opsummary{delay-directory-restore}
+@item --delay-directory-restore
+
+Delay setting modification times and permissions of extracted
+directories until the end of extraction. @xref{Directory Modification Times and Permissions}.
+
+@opsummary{dereference}
@item --dereference
@itemx -h
file that a symbolic link points to, rather than archiving the
symlink. @xref{dereference}.
-@opindex directory, summary
+@opsummary{directory}
@item --directory=@var{dir}
@itemx -C @var{dir}
to @var{dir} before performing any operations. When this option is used
during archive creation, it is order sensitive. @xref{directory}.
-@opindex exclude, summary
+@opsummary{exclude}
@item --exclude=@var{pattern}
When performing operations, @command{tar} will skip files that match
@var{pattern}. @xref{exclude}.
-@opindex exclude-from, summary
+@opsummary{exclude-from}
@item --exclude-from=@var{file}
@itemx -X @var{file}
Similar to @option{--exclude}, except @command{tar} will use the list of
patterns in the file @var{file}. @xref{exclude}.
-@opindex exclude-caches, summary
+@opsummary{exclude-caches}
@item --exclude-caches
-Automatically excludes all directories
-containing a cache directory tag. @xref{exclude}.
+Exclude from dump any directory containing a valid cache directory
+tag file, but still dump the directory node and the tag file itself.
+
+@xref{exclude}.
+
+@opsummary{exclude-caches-under}
+@item --exclude-caches-under
+
+Exclude from dump any directory containing a valid cache directory
+tag file, but still dump the directory node itself.
+
+@xref{exclude}.
+
+@opsummary{exclude-caches-all}
+@item --exclude-caches-all
+
+Exclude from dump any directory containing a valid cache directory
+tag file. @xref{exclude}.
+
+@opsummary{exclude-tag}
+@item --exclude-tag=@var{file}
+
+Exclude from dump any directory containing file named @var{file}, but
+dump the directory node and @var{file} itself. @xref{exclude}.
+
+@opsummary{exclude-tag-under}
+@item --exclude-tag-under=@var{file}
+
+Exclude from dump the contents of any directory containing file
+named @var{file}, but dump the directory node itself. @xref{exclude}.
+
+@opsummary{exclude-tag-all}
+@item --exclude-tag-all=@var{file}
+
+Exclude from dump any directory containing file named @var{file}.
+@xref{exclude}.
+
+@opsummary{exclude-vcs}
+@item --exclude-vcs
+
+Exclude from dump directories and files, that are internal for some
+widely used version control systems.
-@opindex file, summary
+@xref{exclude}.
+
+@opsummary{file}
@item --file=@var{archive}
@itemx -f @var{archive}
performs operations on, rather than @command{tar}'s compilation dependent
default. @xref{file tutorial}.
-@opindex files-from, summary
+@opsummary{files-from}
@item --files-from=@var{file}
@itemx -T @var{file}
or files to operate on, in addition to those specified on the
command-line. @xref{files}.
-@opindex force-local, summary
+@opsummary{force-local}
@item --force-local
-Forces @command{tar} to interpret the filename given to @option{--file}
+Forces @command{tar} to interpret the file name given to @option{--file}
as a local file, even if it looks like a remote tape drive name.
@xref{local and remote archives}.
-@opindex format, summary
+@opsummary{format}
@item --format=@var{format}
+@itemx -H @var{format}
Selects output archive format. @var{Format} may be one of the
following:
@xref{Formats}, for a detailed discussion of these formats.
-@opindex group, summary
+@opsummary{group}
@item --group=@var{group}
-Files added to the @command{tar} archive will have a group id of @var{group},
+Files added to the @command{tar} archive will have a group @acronym{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{}
+a decimal numeric group @acronym{ID}. @xref{override}.
Also see the comments for the @option{--owner=@var{user}} option.
-@opindex gzip, summary
-@opindex gunzip, summary
-@opindex ungzip, summary
+@opsummary{gzip}
+@opsummary{gunzip}
+@opsummary{ungzip}
@item --gzip
@itemx --gunzip
@itemx --ungzip
@command{gzip}, allowing @command{tar} to directly operate on several
kinds of compressed archives transparently. @xref{gzip}.
-@opindex help, summary
+@opsummary{hard-dereference}
+@item --hard-dereference
+When creating an archive, dereference hard links and store the files
+they refer to, instead of creating usual hard link members.
+
+@xref{hard links}.
+
+@opsummary{help}
@item --help
+@itemx -?
@command{tar} will print out a short message summarizing the operations and
options to @command{tar} and exit. @xref{help}.
-@opindex ignore-case, summary
+@opsummary{ignore-case}
@item --ignore-case
-Ignore case when excluding files. @xref{controlling pattern-matching
-with exclude}.
+Ignore case when matching member or file names with
+patterns. @xref{controlling pattern-matching}.
-@opindex ignore-command-error, summary
+@opsummary{ignore-command-error}
@item --ignore-command-error
Ignore exit codes of subprocesses. @xref{Writing to an External Program}.
-@opindex ignore-failed-read, summary
+@opsummary{ignore-failed-read}
@item --ignore-failed-read
Do not exit unsuccessfully merely because an unreadable file was encountered.
@xref{Reading}.
-@opindex ignore-zeros, summary
+@opsummary{ignore-zeros}
@item --ignore-zeros
@itemx -i
With this option, @command{tar} will ignore zeroed blocks in the
archive, which normally signals EOF. @xref{Reading}.
-@opindex incremental, summary
+@opsummary{incremental}
@item --incremental
@itemx -G
-Used to inform @command{tar} that it is working with an old
+Informs @command{tar} that it is working with an old
@acronym{GNU}-format incremental backup archive. It is intended
-primarily for backwards compatibility only. @FIXME{incremental and
-listed-incremental}.
+primarily for backwards compatibility only. @xref{Incremental Dumps},
+for a detailed discussion of incremental archives.
-@opindex index-file, summary
+@opsummary{index-file}
@item --index-file=@var{file}
Send verbose output to @var{file} instead of to standard output.
-@opindex info-script, summary
-@opindex new-volume-script, summary
+@opsummary{info-script}
+@opsummary{new-volume-script}
@item --info-script=@var{script-file}
@itemx --new-volume-script=@var{script-file}
@itemx -F @var{script-file}
@command{tar} fails immediately. @xref{info-script}, for a detailed
discussion of @var{script-file}.
-@opindex interactive, summary
+@opsummary{interactive}
@item --interactive
@itemx --confirmation
@itemx -w
performing potentially destructive options, such as overwriting files.
@xref{interactive}.
-@opindex keep-newer-files, summary
+@opsummary{keep-newer-files}
@item --keep-newer-files
Do not replace existing files that are newer than their archive copies
when extracting files from an archive.
-@opindex keep-old-files, summary
+@opsummary{keep-old-files}
@item --keep-old-files
@itemx -k
Do not overwrite existing files when extracting files from an archive.
@xref{Keep Old Files}.
-@opindex label, summary
+@opsummary{label}
@item --label=@var{name}
@itemx -V @var{name}
@command{tar} will only operate on archives that have a label matching
the pattern specified in @var{name}. @xref{Tape Files}.
-@opindex listed-incremental, summary
+@opsummary{listed-incremental}
@item --listed-incremental=@var{snapshot-file}
@itemx -g @var{snapshot-file}
@command{tar} creates is a new @acronym{GNU}-format incremental
backup, using @var{snapshot-file} to determine which files to backup.
With other operations, informs @command{tar} that the archive is in
-incremental format. @FIXME{incremental and listed-incremental}.
+incremental format. @xref{Incremental Dumps}.
+
+@opsummary{lzma}
+@item --lzma
+@itemx -J
+
+This option tells @command{tar} to read or write archives through
+@command{lzma}. @xref{gzip}.
+
+@item --lzop
+
+This option tells @command{tar} to read or write archives through
+@command{lzop}. @xref{gzip}.
-@opindex mode, summary
+@opsummary{mode}
@item --mode=@var{permissions}
When adding files to an archive, @command{tar} will use
@var{permissions} for the archive members, rather than the permissions
-from the files. The program @command{chmod} and this @command{tar}
-option share the same syntax for what @var{permissions} might be.
-@xref{File permissions, Permissions, File permissions, fileutils,
-@acronym{GNU} file utilities}. This reference also has useful
-information for those not being overly familiar with the Unix
-permission system.
-
-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.
+from the files. @var{permissions} can be specified either as an octal
+number or as symbolic permissions, like with
+@command{chmod}. @xref{override}.
+
+@opsummary{mtime}
+@item --mtime=@var{date}
-@opindex multi-volume, summary
+When adding files to an archive, @command{tar} will use @var{date} as
+the modification time of members when creating archives, instead of
+their actual modification times. The value of @var{date} can be
+either a textual date representation (@pxref{Date input formats}) or a
+name of the existing file, starting with @samp{/} or @samp{.}. In the
+latter case, the modification time of that file is used. @xref{override}.
+
+@opsummary{multi-volume}
@item --multi-volume
@itemx -M
Informs @command{tar} that it should create or otherwise operate on a
multi-volume @command{tar} archive. @xref{Using Multiple Tapes}.
-@opindex new-volume-script, summary
+@opsummary{new-volume-script}
@item --new-volume-script
(see --info-script)
-@opindex seek, summary
-@item --seek
-@itemx -n
-
-Assume that the archive media supports seeks to arbitrary
-locations. Usually @command{tar} determines automatically whether
-the archive can be seeked or not. This option is intended for use
-in cases when such recognition fails.
-
-@opindex newer, summary
+@opsummary{newer}
@item --newer=@var{date}
@itemx --after-date=@var{date}
@itemx -N
is taken to be the name of a file whose data modification time specifies
the date. @xref{after}.
-@opindex newer-mtime, summary
+@opsummary{newer-mtime}
@item --newer-mtime=@var{date}
Like @option{--newer}, but add only files whose
contents have changed (as opposed to just @option{--newer}, which will
-also back up files for which any status information has changed).
+also back up files for which any status information has
+changed). @xref{after}.
-@opindex no-anchored, summary
+@opsummary{no-anchored}
@item --no-anchored
An exclude pattern can match any subsequence of the name's components.
-@xref{controlling pattern-matching with exclude}.
+@xref{controlling pattern-matching}.
+
+@opsummary{no-auto-compress}
+@item --no-auto-compress
+
+Disables automatic compressed format recognition based on the archive
+suffix. @xref{--auto-compress}. @xref{gzip}.
+
+@opsummary{no-check-device}
+@item --no-check-device
+Do not check device numbers when creating a list of modified files
+for incremental archiving. @xref{device numbers}, for
+a detailed description.
-@opindex no-ignore-case, summary
+@opsummary{no-delay-directory-restore}
+@item --no-delay-directory-restore
+
+Modification times and permissions of extracted
+directories are set when all files from this directory have been
+extracted. This is the default.
+@xref{Directory Modification Times and Permissions}.
+
+@opsummary{no-ignore-case}
@item --no-ignore-case
-Use case-sensitive matching when excluding files.
-@xref{controlling pattern-matching with exclude}.
+Use case-sensitive matching.
+@xref{controlling pattern-matching}.
-@opindex no-ignore-command-error, summary
+@opsummary{no-ignore-command-error}
@item --no-ignore-command-error
-Print warnings about subprocesses terminated with a non-zero exit
-code. @xref{Writing to an External Program}.
+Print warnings about subprocesses that terminated with a nonzero exit
+code. @xref{Writing to an External Program}.
+
+@opsummary{no-null}
+@item --no-null
+
+If the @option{--null} option was given previously, this option
+cancels its effect, so that any following @option{--files-from}
+options will expect their file lists to be newline-terminated.
+
+@opsummary{no-overwrite-dir}
+@item --no-overwrite-dir
+
+Preserve metadata of existing directories when extracting files
+from an archive. @xref{Overwrite Old Files}.
+
+@opsummary{no-quote-chars}
+@item --no-quote-chars=@var{string}
+Remove characters listed in @var{string} from the list of quoted
+characters set by the previous @option{--quote-chars} option
+(@pxref{quoting styles}).
-@opindex no-recursion, summary
+@opsummary{no-recursion}
@item --no-recursion
With this option, @command{tar} will not recurse into directories.
@xref{recurse}.
-@opindex no-same-owner, summary
+@opsummary{no-same-owner}
@item --no-same-owner
@itemx -o
specified in the @command{tar} archive. This the default behavior
for ordinary users.
-@opindex no-same-permissions, summary
+@opsummary{no-same-permissions}
@item --no-same-permissions
When extracting an archive, subtract the user's umask from files from
the permissions specified in the archive. This is the default behavior
for ordinary users.
-@opindex no-wildcards, summary
+@opsummary{no-unquote}
+@item --no-unquote
+Treat all input file or member names literally, do not interpret
+escape sequences. @xref{input name quoting}.
+
+@opsummary{no-wildcards}
@item --no-wildcards
-Do not use wildcards when excluding files.
-@xref{controlling pattern-matching with exclude}.
+Do not use wildcards.
+@xref{controlling pattern-matching}.
-@opindex no-wildcards-match-slash, summary
+@opsummary{no-wildcards-match-slash}
@item --no-wildcards-match-slash
-Wildcards do not match @samp{/} when excluding files.
-@xref{controlling pattern-matching with exclude}.
+Wildcards do not match @samp{/}.
+@xref{controlling pattern-matching}.
-@opindex null, summary
+@opsummary{null}
@item --null
When @command{tar} is using the @option{--files-from} option, this option
-instructs @command{tar} to expect filenames terminated with @option{NUL}, so
+instructs @command{tar} to expect file names terminated with @acronym{NUL}, so
@command{tar} can correctly work with file names that contain newlines.
@xref{nul}.
-@opindex numeric-owner, summary
+@opsummary{numeric-owner}
@item --numeric-owner
This option will notify @command{tar} that it should use numeric user
@xref{Attributes}.
@item -o
-When extracting files, this option is a synonym for
-@option{--no-same-owner}, i.e. it prevents @command{tar} from
+The function of this option depends on the action @command{tar} is
+performing. When extracting files, @option{-o} is a synonym for
+@option{--no-same-owner}, i.e., it prevents @command{tar} from
restoring ownership of files being extracted.
-When creating an archive, @option{-o} is a synonym for
+When creating an archive, it is a synonym for
@option{--old-archive}. This behavior is for compatibility
with previous versions of @GNUTAR{}, and will be
-removed in the future releases.
+removed in future releases.
@xref{Changes}, for more information.
-@opindex occurrence, summary
+@opsummary{occurrence}
@item --occurrence[=@var{number}]
This option can be used in conjunction with one of the subcommands
@end smallexample
@noindent
-will extract the first occurrence of @file{filename} from @file{archive.tar}
+will extract the first occurrence of the member @file{filename} from @file{archive.tar}
and will terminate without scanning to the end of the archive.
-@opindex old-archive, summary
+@opsummary{old-archive}
@item --old-archive
Synonym for @option{--format=v7}.
-@opindex one-file-system, summary
+@opsummary{one-file-system}
@item --one-file-system
-@itemx -l
Used when creating an archive. Prevents @command{tar} from recursing into
directories that are on different file systems from the current
directory.
-Earlier versions of @GNUTAR{} understood @option{-l} as a
-synonym for @option{--one-file-system}. Although such usage is still
-allowed in the present version, it is @emph{strongly discouraged}.
-The future versions of @GNUTAR{} will use @option{-l} as
-a synonym for @option{--check-links}.
-
-@xref{Changes}, for more information.
-
-@opindex overwrite, summary
+@opsummary{overwrite}
@item --overwrite
Overwrite existing files and directory metadata when extracting files
from an archive. @xref{Overwrite Old Files}.
-@opindex overwrite-dir, summary
+@opsummary{overwrite-dir}
@item --overwrite-dir
Overwrite the metadata of existing directories when extracting files
from an archive. @xref{Overwrite Old Files}.
-@opindex owner, summary
+@opsummary{owner}
@item --owner=@var{user}
Specifies that @command{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{}
-
-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.
+this interpretation fails, it has to be a decimal numeric user @acronym{ID}.
+@xref{override}.
This option does not affect extraction from archives.
-@opindex pax-option, summary
+@opsummary{pax-option}
@item --pax-option=@var{keyword-list}
-@FIXME{Such a detailed description does not belong there, move it elsewhere.}
This option is meaningful only with @acronym{POSIX.1-2001} archives
(@pxref{posix}). It modifies the way @command{tar} handles the
extended header keywords. @var{Keyword-list} is a comma-separated
-list of keyword options, each keyword option taking one of
-the following forms:
-
-@table @asis
-@item delete=@var{pattern}
-When used with one of archive-creation commands,
-this option instructs @command{tar} to omit from extended header records
-that it produces any keywords matching the string @var{pattern}.
-
-When used in extract or list mode, this option instructs tar
-to ignore any keywords matching the given @var{pattern} in the extended
-header records. In both cases, matching is performed using the pattern
-matching notation described in @acronym{POSIX 1003.2}, 3.13
-(See @cite{glob(7)}). For example:
-
-@smallexample
---pax-option delete=security.*
-@end smallexample
-
-would suppress security-related information.
-
-@item exthdr.name=@var{string}
-
-This keyword allows user control over the name that is written into the
-ustar header blocks for the extended headers. The name is obtained
-from @var{string} after substituting the following meta-characters:
-
-@multitable @columnfractions .30 .70
-@headitem Meta-character @tab Replaced By
-@item %d @tab The directory name of the file, equivalent to the
-result of the @command{dirname} utility on the translated pathname.
-@item %f @tab The filename of the file, equivalent to the result
-of the @command{basename} utility on the translated pathname.
-@item %p @tab The process ID of the @command{tar} process.
-@item %% @tab A @samp{%} character.
-@end multitable
-
-Any other @samp{%} characters in @var{string} produce undefined
-results.
-
-If no option @samp{exthdr.name=string} is specified, @command{tar}
-will use the following default value:
-
-@smallexample
-%d/PaxHeaders.%p/%f
-@end smallexample
+list of keyword options. @xref{PAX keywords}, for a detailed
+discussion.
-@item globexthdr.name=@var{string}
-This keyword allows user control over the name that is written into
-the ustar header blocks for global extended header records. The name
-shall will be obtained from the contents of @var{string}, after the
-following character substitutions have been made:
-
-@multitable @columnfractions .30 .70
-@headitem Meta-character @tab Replaced By
-@item %n @tab An integer that represents the
-sequence number of the global extended header record in the archive,
-starting at 1.
-@item %p @tab The process ID of the @command{tar} process.
-@item %% @tab A @samp{%} character.
-@end multitable
-
-Any other @samp{%} characters in string produce undefined results.
-
-If no option @samp{globexthdr.name=string} is specified, @command{tar}
-will use the following default value:
-
-@smallexample
-$TMPDIR/GlobalHead.%p.%n
-@end smallexample
-
-@noindent
-where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
-environment variable. If @var{TMPDIR} is not set, @command{tar}
-uses @samp{/tmp}.
-
-@item @var{keyword}=@var{value}
-When used with one of archive-creation commands, these keyword/value pairs
-will be included at the beginning of the archive in a global extended
-header record. When used with one of archive-reading commands,
-@command{tar} will behave as if it has encountered these keyword/value
-pairs at the beginning of the archive in a global extended header
-record.
-
-@item @var{keyword}:=@var{value}
-When used with one of archive-creation commands, these keyword/value pairs
-will be included as records at the beginning of an extended header for
-each file. This is effectively equivalent to @var{keyword}=@var{value}
-form except that it creates no global extended header records.
-
-When used with one of archive-reading commands, @command{tar} will
-behave as if these keyword/value pairs were included as records at the
-end of each extended header; thus, they will override any global or
-file-specific extended header record keywords of the same names.
-For example, in the command:
-
-@smallexample
-tar --format=posix --create \
- --file archive --pax-option gname:=user .
-@end smallexample
-
-the group name will be forced to a new value for all files
-stored in the archive.
-@end table
-
-@opindex portability, summary
+@opsummary{portability}
@item --portability
@itemx --old-archive
Synonym for @option{--format=v7}.
-@opindex posix, summary
+@opsummary{posix}
@item --posix
Same as @option{--format=posix}.
-@opindex preserve, summary
+@opsummary{preserve}
@item --preserve
Synonymous with specifying both @option{--preserve-permissions} and
@option{--same-order}. @xref{Setting Access Permissions}.
-@opindex preserve-order, summary
+@opsummary{preserve-order}
@item --preserve-order
(See @option{--same-order}; @pxref{Reading}.)
-@opindex preserve-permissions, summary
-@opindex same-permissions, summary
+@opsummary{preserve-permissions}
+@opsummary{same-permissions}
@item --preserve-permissions
@itemx --same-permissions
@itemx -p
Specifying this option instructs @command{tar} that it should use the
permissions directly from the archive. @xref{Setting Access Permissions}.
-@opindex read-full-records, summary
+@opsummary{quote-chars}
+@item --quote-chars=@var{string}
+Always quote characters from @var{string}, even if the selected
+quoting style would not quote them (@pxref{quoting styles}).
+
+@opsummary{quoting-style}
+@item --quoting-style=@var{style}
+Set quoting style to use when printing member and file names
+(@pxref{quoting styles}). Valid @var{style} values are:
+@code{literal}, @code{shell}, @code{shell-always}, @code{c},
+@code{escape}, @code{locale}, and @code{clocale}. Default quoting
+style is @code{escape}, unless overridden while configuring the
+package.
+
+@opsummary{read-full-records}
@item --read-full-records
@itemx -B
Specifies that @command{tar} should reblock its input, for reading
from pipes on systems with buggy implementations. @xref{Reading}.
-@opindex record-size, summary
+@opsummary{record-size}
@item --record-size=@var{size}
Instructs @command{tar} to use @var{size} bytes per record when accessing the
archive. @xref{Blocking Factor}.
-@opindex recursion, summary
+@opsummary{recursion}
@item --recursion
-With this option, @command{tar} recurses into directories.
+With this option, @command{tar} recurses into directories (default).
@xref{recurse}.
-@opindex recursive-unlink, summary
+@opsummary{recursive-unlink}
@item --recursive-unlink
Remove existing
directory hierarchies before extracting directories of the same name
from the archive. @xref{Recursive Unlink}.
-@opindex remove-files, summary
+@opsummary{remove-files}
@item --remove-files
Directs @command{tar} to remove the source file from the file system after
appending it to an archive. @xref{remove files}.
-@opindex restrict, summary
+@opsummary{restrict}
@item --restrict
Disable use of some potentially harmful @command{tar} options.
-Currently this option disables shell invocaton from multi-volume menu
+Currently this option disables shell invocation from multi-volume menu
(@pxref{Using Multiple Tapes}).
-@opindex rmt-command, summary
+@opsummary{rmt-command}
@item --rmt-command=@var{cmd}
Notifies @command{tar} that it should use @var{cmd} instead of
the default @file{/usr/libexec/rmt} (@pxref{Remote Tape Server}).
-@opindex rsh-command, summary
+@opsummary{rsh-command}
@item --rsh-command=@var{cmd}
Notifies @command{tar} that is should use @var{cmd} to communicate with remote
devices. @xref{Device}.
-@opindex same-order, summary
+@opsummary{same-order}
@item --same-order
@itemx --preserve-order
@itemx -s
arguments has already been sorted to match the order of files in the
archive. @xref{Reading}.
-@opindex same-owner, summary
+@opsummary{same-owner}
@item --same-owner
When extracting an archive, @command{tar} will attempt to preserve the owner
This is the default behavior for the superuser; this option has an
effect only for ordinary users. @xref{Attributes}.
-@opindex same-permissions, summary
+@opsummary{same-permissions}
@item --same-permissions
(See @option{--preserve-permissions}; @pxref{Setting Access Permissions}.)
-@opindex show-defaults, summary
+@opsummary{seek}
+@item --seek
+@itemx -n
+
+Assume that the archive media supports seeks to arbitrary
+locations. Usually @command{tar} determines automatically whether
+the archive can be seeked or not. This option is intended for use
+in cases when such recognition fails.
+
+@opsummary{show-defaults}
@item --show-defaults
Displays the default options used by @command{tar} and exits
@smallexample
$ tar --show-defaults
---format=gnu -f- -b20
+--format=gnu -f- -b20 --quoting-style=escape \
+--rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
@end smallexample
-@opindex show-omitted-dirs, summary
+@opsummary{show-omitted-dirs}
@item --show-omitted-dirs
-Instructs @command{tar} to mention directories its skipping over when
+Instructs @command{tar} to mention the directories it is skipping when
operating on a @command{tar} archive. @xref{show-omitted-dirs}.
-@opindex show-stored-names, summary
-@item --show-stored-names
+@opsummary{show-transformed-names}
+@opsummary{show-stored-names}
+@item --show-transformed-names
+@itemx --show-stored-names
-This option has effect only when used in conjunction with one of
-archive creation operations. It instructs tar to list the member names
-stored in the archive, as opposed to the actual file
+Display file or member names after applying any transformations
+(@pxref{transform}). In particular, when used in conjunction with one of
+the archive creation operations it instructs @command{tar} to list the
+member names stored in the archive, as opposed to the actual file
names. @xref{listing member and file names}.
-@opindex sparse, summary
+@opsummary{sparse}
@item --sparse
@itemx -S
Invokes a @acronym{GNU} extension when adding files to an archive that handles
sparse files efficiently. @xref{sparse}.
-@opindex starting-file, summary
+@opsummary{sparse-version}
+@item --sparse-version=@var{version}
+
+Specifies the @dfn{format version} to use when archiving sparse
+files. Implies @option{--sparse}. @xref{sparse}. For the description
+of the supported sparse formats, @xref{Sparse Formats}.
+
+@opsummary{starting-file}
@item --starting-file=@var{name}
@itemx -K @var{name}
files in the archive until it finds one that matches @var{name}.
@xref{Scarce}.
-@opindex strip-components, summary
+@opsummary{strip-components}
@item --strip-components=@var{number}
Strip given @var{number} of leading components from file names before
-extraction.@footnote{This option was called @option{--strip-path} in
-version 1.14.} For example, if archive @file{archive.tar} contained
+extraction. For example, if archive @file{archive.tar} contained
@file{/some/file/name}, then running
@smallexample
@end smallexample
@noindent
-would extracted this file to file @file{name}.
+would extract this file to file @file{name}.
-@opindex suffix, summary
+@opsummary{suffix}, summary
@item --suffix=@var{suffix}
Alters the suffix @command{tar} uses when backing up files from the default
@samp{~}. @xref{backup}.
-@opindex tape-length, summary
+@opsummary{tape-length}
@item --tape-length=@var{num}
@itemx -L @var{num}
Specifies the length of tapes that @command{tar} is writing as being
@w{@var{num} x 1024} bytes long. @xref{Using Multiple Tapes}.
-@opindex test-label, summary
+@opsummary{test-label}
@item --test-label
Reads the volume label. If an argument is specified, test whether it
matches the volume label. @xref{--test-label option}.
-@opindex to-command, summary
+@opsummary{to-command}
@item --to-command=@var{command}
During extraction @command{tar} will pipe extracted files to the
-standard input of @var{command}. @xref{Writing to an External Program}.
+standard input of @var{command}. @xref{Writing to an External Program}.
-@opindex to-stdout, summary
+@opsummary{to-stdout}
@item --to-stdout
@itemx -O
During extraction, @command{tar} will extract files to stdout rather
than to the file system. @xref{Writing to Standard Output}.
-@opindex totals, summary
-@item --totals
+@opsummary{totals}
+@item --totals[=@var{signo}]
-Displays the total number of bytes written after creating an archive.
-@xref{verbose}.
+Displays the total number of bytes transferred when processing an
+archive. If an argument is given, these data are displayed on
+request, when signal @var{signo} is delivered to @command{tar}.
+@xref{totals}.
-@opindex touch, summary
+@opsummary{touch}
@item --touch
@itemx -m
rather than the data modification time stored in the archive.
@xref{Data Modification Times}.
-@opindex uncompress, summary
+@opsummary{transform}
+@opsummary{xform}
+@item --transform=@var{sed-expr}
+@itemx --xform=@var{sed-expr}
+Transform file or member names using @command{sed} replacement expression
+@var{sed-expr}. For example,
+
+@smallexample
+$ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
+@end smallexample
+
+@noindent
+will add to @file{archive} files from the current working directory,
+replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
+discussion, @xref{transform}.
+
+To see transformed member names in verbose listings, use
+@option{--show-transformed-names} option
+(@pxref{show-transformed-names}).
+
+@opsummary{uncompress}
@item --uncompress
(See @option{--compress}. @pxref{gzip})
-@opindex ungzip, summary
+@opsummary{ungzip}
@item --ungzip
(See @option{--gzip}. @pxref{gzip})
-@opindex unlink-first, summary
+@opsummary{unlink-first}
@item --unlink-first
@itemx -U
Directs @command{tar} to remove the corresponding file from the file
system before extracting it from the archive. @xref{Unlink First}.
-@opindex use-compress-program, summary
+@opsummary{unquote}
+@item --unquote
+Enable unquoting input file or member names (default). @xref{input
+name quoting}.
+
+@opsummary{use-compress-program}
@item --use-compress-program=@var{prog}
+@itemx -I=@var{prog}
Instructs @command{tar} to access the archive through @var{prog}, which is
presumed to be a compression program of some sort. @xref{gzip}.
-@opindex utc, summary
+@opsummary{utc}
@item --utc
Display file modification dates in @acronym{UTC}. This option implies
@option{--verbose}.
-@opindex verbose, summary
+@opsummary{verbose}
@item --verbose
@itemx -v
-Specifies that @command{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.
+Specifies that @command{tar} should be more verbose about the
+operations it is performing. This option can be specified multiple
+times for some operations to increase the amount of information displayed.
@xref{verbose}.
-@opindex verify, summary
+@opsummary{verify}
@item --verify
@itemx -W
Verifies that the archive was correctly written when creating an
archive. @xref{verify}.
-@opindex version, summary
+@opsummary{version}
@item --version
-@command{tar} will print an informational message about what version
-it is and a copyright message, some credits, and then exit.
+Print information about the program's name, version, origin and legal
+status, all on standard output, and then exit successfully.
@xref{help}.
-@opindex volno-file, summary
+@opsummary{volno-file}
@item --volno-file=@var{file}
-Used in conjunction with @option{--multi-volume}. @command{tar} will keep track
-of which volume of a multi-volume archive its working in @var{file}.
-@xref{volno-file}.
+Used in conjunction with @option{--multi-volume}. @command{tar} will
+keep track of which volume of a multi-volume archive it is working in
+@var{file}. @xref{volno-file}.
-@opindex wildcards, summary
+@opsummary{wildcards}
@item --wildcards
-Use wildcards when excluding files.
-@xref{controlling pattern-matching with exclude}.
+Use wildcards when matching member names with patterns.
+@xref{controlling pattern-matching}.
-@opindex wildcards-match-slash, summary
+@opsummary{wildcards-match-slash}
@item --wildcards-match-slash
-Wildcards match @samp{/} when excluding files.
-@xref{controlling pattern-matching with exclude}.
+Wildcards match @samp{/}.
+@xref{controlling pattern-matching}.
@end table
@node Short Option Summary
Here is an alphabetized list of all of the short option forms, matching
them with the equivalent long option.
-@table @option
-
-@item -A
-
-@option{--concatenate}
-
-@item -B
-
-@option{--read-full-records}
-
-@item -C
-
-@option{--directory}
-
-@item -F
-
-@option{--info-script}
-
-@item -G
-
-@option{--incremental}
-
-@item -K
-
-@option{--starting-file}
-
-@item -L
-
-@option{--tape-length}
-
-@item -M
-
-@option{--multi-volume}
-
-@item -N
-
-@option{--newer}
-
-@item -O
-
-@option{--to-stdout}
+@multitable @columnfractions 0.20 0.80
+@headitem Short Option @tab Reference
-@item -P
+@item -A @tab @ref{--concatenate}.
-@option{--absolute-names}
+@item -B @tab @ref{--read-full-records}.
-@item -R
+@item -C @tab @ref{--directory}.
-@option{--block-number}
+@item -F @tab @ref{--info-script}.
-@item -S
-
-@option{--sparse}
-
-@item -T
-
-@option{--files-from}
-
-@item -U
-
-@option{--unlink-first}
-
-@item -V
+@item -G @tab @ref{--incremental}.
-@option{--label}
+@item -J @tab @ref{--lzma}.
-@item -W
-
-@option{--verify}
-
-@item -X
-
-@option{--exclude-from}
+@item -K @tab @ref{--starting-file}.
-@item -Z
-
-@option{--compress}
+@item -L @tab @ref{--tape-length}.
-@item -b
+@item -M @tab @ref{--multi-volume}.
-@option{--blocking-factor}
+@item -N @tab @ref{--newer}.
-@item -c
+@item -O @tab @ref{--to-stdout}.
-@option{--create}
+@item -P @tab @ref{--absolute-names}.
-@item -d
+@item -R @tab @ref{--block-number}.
-@option{--compare}
-
-@item -f
+@item -S @tab @ref{--sparse}.
-@option{--file}
+@item -T @tab @ref{--files-from}.
-@item -g
+@item -U @tab @ref{--unlink-first}.
-@option{--listed-incremental}
+@item -V @tab @ref{--label}.
-@item -h
+@item -W @tab @ref{--verify}.
-@option{--dereference}
+@item -X @tab @ref{--exclude-from}.
-@item -i
+@item -Z @tab @ref{--compress}.
-@option{--ignore-zeros}
+@item -b @tab @ref{--blocking-factor}.
-@item -j
+@item -c @tab @ref{--create}.
-@option{--bzip2}
+@item -d @tab @ref{--compare}.
-@item -k
+@item -f @tab @ref{--file}.
-@option{--keep-old-files}
+@item -g @tab @ref{--listed-incremental}.
-@item -l
+@item -h @tab @ref{--dereference}.
-@option{--one-file-system}. Use of this short option is deprecated. It
-is retained for compatibility with the earlier versions of GNU
-@command{tar}, and will be changed in future releases.
+@item -i @tab @ref{--ignore-zeros}.
-@xref{Changes}, for more information.
+@item -j @tab @ref{--bzip2}.
-@item -m
+@item -k @tab @ref{--keep-old-files}.
-@option{--touch}
+@item -l @tab @ref{--check-links}.
-@item -o
+@item -m @tab @ref{--touch}.
-When creating --- @option{--no-same-owner}, when extracting ---
-@option{--portability}.
+@item -o @tab When creating, @ref{--no-same-owner}, when extracting ---
+@ref{--portability}.
-The later usage is deprecated. It is retained for compatibility with
-the earlier versions of @GNUTAR{}. In the future releases
+The latter usage is deprecated. It is retained for compatibility with
+the earlier versions of @GNUTAR{}. In future releases
@option{-o} will be equivalent to @option{--no-same-owner} only.
-@item -p
-
-@option{--preserve-permissions}
-
-@item -r
-
-@option{--append}
-
-@item -s
-
-@option{--same-order}
-
-@item -t
-
-@option{--list}
-
-@item -u
-
-@option{--update}
+@item -p @tab @ref{--preserve-permissions}.
-@item -v
+@item -r @tab @ref{--append}.
-@option{--verbose}
+@item -s @tab @ref{--same-order}.
-@item -w
+@item -t @tab @ref{--list}.
-@option{--interactive}
+@item -u @tab @ref{--update}.
-@item -x
+@item -v @tab @ref{--verbose}.
-@option{--extract}
+@item -w @tab @ref{--interactive}.
-@item -z
+@item -x @tab @ref{--extract}.
-@option{--gzip}
+@item -z @tab @ref{--gzip}.
-@end table
+@end multitable
@node help
@section @GNUTAR{} documentation
@cindex Version of the @command{tar} program
Being careful, the first thing is really checking that you are using
@GNUTAR{}, indeed. The @option{--version} option
-will generate a message giving confirmation that you are using
-@GNUTAR{}, with the precise version of @GNUTAR{}
-you are using. @command{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:
+causes @command{tar} to print information about its name, version,
+origin and legal status, all on standard output, and then exit
+successfully. For example, @w{@samp{tar --version}} might print:
@smallexample
-tar (@acronym{GNU} tar) @value{VERSION}
+tar (GNU tar) @value{VERSION}
+Copyright (C) 2008 Free Software Foundation, Inc.
+This is free software. You may redistribute copies of it under the terms
+of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
+There is NO WARRANTY, to the extent permitted by law.
+
+Written by John Gilmore and Jay Fenlason.
@end smallexample
@noindent
contains@footnote{There are plans to merge the @command{cpio} and
@command{tar} packages into a single one which would be called
@code{paxutils}. So, who knows if, one of this days, the
-@option{--version} would not yield @w{@samp{tar (@acronym{GNU}
+@option{--version} would not output @w{@samp{tar (@acronym{GNU}
paxutils) 3.2}}}.
@cindex Obtaining help
@cindex Listing all @command{tar} options
-@opindex help, introduction
+@xopindex{help, introduction}
Another thing you might want to do is checking the spelling or meaning
of some particular @command{tar} option, without resorting to this
manual, for once you have carefully read it. @GNUTAR{}
@command{tar} options have long description lines and the above
command will list only the first of them.
+The exact look of the option summary displayed by @kbd{tar --help} is
+configurable. @xref{Configuring Help Summary}, for a detailed description.
+
@opindex usage
If you only wish to check the spelling of an option, running @kbd{tar
--usage} may be a better choice. This will display a terse list of
back to the full documentation for precise points. If you are reading
this paragraph, you already have the @command{tar} manual in some
form. This manual is available in a variety of forms from
-@url{http://www.gnu.org/software/tar/manual}. It may printed out of the @GNUTAR{}
+@url{http://www.gnu.org/software/tar/manual}. It may be printed out of the @GNUTAR{}
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
@opindex show-defaults
@GNUTAR{} has some predefined defaults that are used when you do not
-explicitely specify another values. To obtain a list of such
+explicitly specify another values. To obtain a list of such
defaults, use @option{--show-defaults} option. This will output the
values in the form of @command{tar} command line options:
@smallexample
@group
@kbd{tar --show-defaults}
---format=gnu -f- -b20 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
+--format=gnu -f- -b20 --quoting-style=escape
+--rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
@end group
@end smallexample
+@noindent
+Notice, that this option outputs only one line. The example output above
+has been split to fit page boundaries.
+
@noindent
The above output shows that this version of @GNUTAR{} defaults to
using @samp{gnu} archive format (@pxref{Formats}), it uses standard
(@option{-v}) option causes @command{tar} to print the name of each
file or archive member as it is processed. This and the other options
which make @command{tar} print status information can be useful in
-monitoring @command{tar}.
+monitoring @command{tar}.
With @option{--create} or @option{--extract}, @option{--verbose} used
once just prints the names of the files or members as they are processed.
Using it twice causes @command{tar} to print a longer listing
-(reminiscent of @samp{ls -l}) for each member. Since @option{--list}
-already prints the names of the members, @option{--verbose} used once
-with @option{--list} causes @command{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:
+(@xref{verbose member listing}, for the description) for each member.
+Since @option{--list} already prints the names of the members,
+@option{--verbose} used once with @option{--list} causes @command{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:
@smallexample
$ @kbd{tar --extract --file=archive.tar --verbose --verbose}
verbose output to @var{file} rather than to standard output or standard
error.
+@anchor{totals}
@cindex Obtaining total status information
@opindex totals
-The @option{--totals} option---which is only meaningful when used with
-@option{--create} (@option{-c})---causes @command{tar} to print the total
-amount written to the archive, after it has been fully created.
+The @option{--totals} option causes @command{tar} to print on the
+standard error the total amount of bytes transferred when processing
+an archive. When creating or appending to an archive, this option
+prints the number of bytes written to the archive and the average
+speed at which they have been written, e.g.:
+
+@smallexample
+@group
+$ @kbd{tar -c -f archive.tar --totals /home}
+Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
+@end group
+@end smallexample
+
+When reading an archive, this option displays the number of bytes
+read:
+
+@smallexample
+@group
+$ @kbd{tar -x -f archive.tar --totals}
+Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
+@end group
+@end smallexample
+
+Finally, when deleting from an archive, the @option{--totals} option
+displays both numbers plus number of bytes removed from the archive:
+
+@smallexample
+@group
+$ @kbd{tar --delete -f foo.tar --totals --wildcards '*~'}
+Total bytes read: 9543680 (9.2MiB, 201MiB/s)
+Total bytes written: 3829760 (3.7MiB, 81MiB/s)
+Total bytes deleted: 1474048
+@end group
+@end smallexample
+You can also obtain this information on request. When
+@option{--totals} is used with an argument, this argument is
+interpreted as a symbolic name of a signal, upon delivery of which the
+statistics is to be printed:
+
+@table @option
+@item --totals=@var{signo}
+Print statistics upon delivery of signal @var{signo}. Valid arguments
+are: @code{SIGHUP}, @code{SIGQUIT}, @code{SIGINT}, @code{SIGUSR1} and
+@code{SIGUSR2}. Shortened names without @samp{SIG} prefix are also
+accepted.
+@end table
+
+Both forms of @option{--totals} option can be used simultaneously.
+Thus, @kbd{tar -x --totals --totals=USR1} instructs @command{tar} to
+extract all members from its default archive and print statistics
+after finishing the extraction, as well as when receiving signal
+@code{SIGUSR1}.
+
+@anchor{Progress information}
@cindex Progress information
-@opindex checkpoint
The @option{--checkpoint} option prints an occasional message
-as @command{tar} reads or writes the archive. In fact, it prints
-a message each 10 records read or written. It is designed for
+as @command{tar} reads or writes the archive. It is designed for
those who don't need the more detailed (and voluminous) output of
-@option{--block-number} (@option{-R}), but do want visual confirmation that @command{tar}
-is actually making forward progress.
+@option{--block-number} (@option{-R}), but do want visual confirmation
+that @command{tar} is actually making forward progress. By default it
+prints a message each 10 records read or written. This can be changed
+by giving it a numeric argument after an equal sign:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000} /var
+tar: Write checkpoint 1000
+tar: Write checkpoint 2000
+tar: Write checkpoint 3000
+@end smallexample
+
+This example shows the default checkpoint message used by
+@command{tar}. If you place a dot immediately after the equal
+sign, it will print a @samp{.} at each checkpoint@footnote{This is
+actually a shortcut for @option{--checkpoint=@var{n}
+--checkpoint-action=dot}. @xref{checkpoints, dot}.}. For example:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=.1000} /var
+...
+@end smallexample
-@FIXME{There is some confusion here. It seems that -R once wrote a
-message at @samp{every} record read or written.}
+The @option{--checkpoint} option provides a flexible mechanism for
+executing arbitrary actions upon hitting checkpoints, see the next
+section (@pxref{checkpoints}), for more information on it.
@opindex show-omitted-dirs
@anchor{show-omitted-dirs}
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 @option{--exclude=@var{pattern}} option, or
-some other reason.
+it might be excluded by the use of the
+@option{--exclude=@var{pattern}} option, or some other reason.
@opindex block-number
@cindex Block number where error occurred
favor of the tape where the file appears earliest (closest to the
front of the tape). @xref{backup}.
+@node checkpoints
+@section Checkpoints
+@cindex checkpoints, defined
+@opindex checkpoint
+@opindex checkpoint-action
+
+A @dfn{checkpoint} is a moment of time before writing @var{n}th record to
+the archive (a @dfn{write checkpoint}), or before reading @var{n}th record
+from the archive (a @dfn{read checkpoint}). Checkpoints allow to
+periodically execute arbitrary actions.
+
+The checkpoint facility is enabled using the following option:
+
+@table @option
+@xopindex{checkpoint, defined}
+@item --checkpoint[=@var{n}]
+Schedule checkpoints before writing or reading each @var{n}th record.
+The default value for @var{n} is 10.
+@end table
+
+A list of arbitrary @dfn{actions} can be executed at each checkpoint.
+These actions include: pausing, displaying textual messages, and
+executing arbitrary external programs. Actions are defined using
+the @option{--checkpoint-action} option.
+
+@table @option
+@xopindex{checkpoint-action, defined}
+@item --checkpoint-action=@var{action}
+Execute an @var{action} at each checkpoint.
+@end table
+
+@cindex @code{echo}, checkpoint action
+The simplest value of @var{action} is @samp{echo}. It instructs
+@command{tar} to display the default message on the standard error
+stream upon arriving at each checkpoint. The default message is (in
+@acronym{POSIX} locale) @samp{Write checkpoint @var{n}}, for write
+checkpoints, and @samp{Read checkpoint @var{n}}, for read checkpoints.
+Here, @var{n} represents ordinal number of the checkpoint.
+
+In another locales, translated versions of this message are used.
+
+This is the default action, so running:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000 --checkpoint-action=echo} /var
+@end smallexample
+
+@noindent
+is equivalent to:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000} /var
+@end smallexample
+
+The @samp{echo} action also allows to supply a customized message.
+You do so by placing an equals sign and the message right after it,
+e.g.:
+
+@smallexample
+--checkpoint-action="echo=Hit %s checkpoint #%u"
+@end smallexample
+
+The @samp{%s} and @samp{%u} in the above example are
+@dfn{meta-characters}. The @samp{%s} meta-character is replaced with
+the @dfn{type} of the checkpoint: @samp{write} or
+@samp{read} (or a corresponding translated version in locales other
+than @acronym{POSIX}). The @samp{%u} meta-character is replaced with
+the ordinal number of the checkpoint. Thus, the above example could
+produce the following output when used with the @option{--create}
+option:
+
+@smallexample
+tar: Hit write checkpoint #10
+tar: Hit write checkpoint #20
+tar: Hit write checkpoint #30
+@end smallexample
+
+Aside from meta-character expansion, the message string is subject to
+@dfn{unquoting}, during which the backslash @dfn{escape sequences} are
+replaced with their corresponding @acronym{ASCII} characters
+(@pxref{escape sequences}). E.g. the following action will produce an
+audible bell and the message described above at each checkpoint:
+
+@smallexample
+--checkpoint-action='echo=\aHit %s checkpoint #%u'
+@end smallexample
+
+@cindex @code{bell}, checkpoint action
+There is also a special action which produces an audible signal:
+@samp{bell}. It is not equivalent to @samp{echo='\a'}, because
+@samp{bell} sends the bell directly to the console (@file{/dev/tty}),
+whereas @samp{echo='\a'} sends it to the standard error.
+
+@cindex @code{ttyout}, checkpoint action
+The @samp{ttyout=@var{string}} action outputs @var{string} to
+@file{/dev/tty}, so it can be used even if the standard output is
+redirected elsewhere. The @var{string} is subject to the same
+modifications as with @samp{echo} action. In contrast to the latter,
+@samp{ttyout} does not prepend @command{tar} executable name to the
+string, nor does it output a newline after it. For example, the
+following action will print the checkpoint message at the same screen
+line, overwriting any previous message:
+
+@smallexample
+--checkpoint-action="ttyout=\rHit %s checkpoint #%u"
+@end smallexample
+
+@cindex @code{dot}, checkpoint action
+Another available checkpoint action is @samp{dot} (or @samp{.}). It
+instructs @command{tar} to print a single dot on the standard listing
+stream, e.g.:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000 --checkpoint-action=dot} /var
+...
+@end smallexample
+
+For compatibility with previous @GNUTAR{} versions, this action can
+be abbreviated by placing a dot in front of the checkpoint frequency,
+as shown in the previous section.
+
+@cindex @code{sleep}, checkpoint action
+Yet another action, @samp{sleep}, pauses @command{tar} for a specified
+amount of seconds. The following example will stop for 30 seconds at each
+checkpoint:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000 --checkpoint-action=sleep=30}
+@end smallexample
+
+@cindex @code{exec}, checkpoint action
+Finally, the @code{exec} action executes a given external program.
+For example:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint}
+@end smallexample
+
+This program is executed using @command{/bin/sh -c}, with no
+additional arguments. Its exit code is ignored. It gets a copy of
+@command{tar}'s environment plus the following variables:
+
+@table @env
+@vrindex TAR_VERSION, checkpoint script environment
+@item TAR_VERSION
+@GNUTAR{} version number.
+
+@vrindex TAR_ARCHIVE, checkpoint script environment
+@item TAR_ARCHIVE
+The name of the archive @command{tar} is processing.
+
+@vrindex TAR_BLOCKING_FACTOR, checkpoint script environment
+@item TAR_BLOCKING_FACTOR
+Current blocking factor (@pxref{Blocking}).
+
+@vrindex TAR_CHECKPOINT, checkpoint script environment
+@item TAR_CHECKPOINT
+Number of the checkpoint.
+
+@vrindex TAR_SUBCOMMAND, checkpoint script environment
+@item TAR_SUBCOMMAND
+A short option describing the operation @command{tar} is executing.
+@xref{Operations}, for a complete list of subcommand options.
+
+@vrindex TAR_FORMAT, checkpoint script environment
+@item TAR_FORMAT
+Format of the archive being processed. @xref{Formats}, for a complete
+list of archive format names.
+@end table
+
+Any number of actions can be defined, by supplying several
+@option{--checkpoint-action} options in the command line. For
+example, the command below displays two messages, pauses
+execution for 30 seconds and executes the @file{/sbin/cpoint} script:
+
+@example
+@group
+$ @kbd{tar -c -f arc.tar \
+ --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
+ --checkpoint-action='echo=Sleeping for 30 seconds' \
+ --checkpoint-action='sleep=30' \
+ --checkpoint-action='exec=/sbin/cpoint'}
+@end group
+@end example
+
+This example also illustrates the fact that
+@option{--checkpoint-action} can be used without
+@option{--checkpoint}. In this case, the default checkpoint frequency
+(at each 10th record) is assumed.
+
@node interactive
@section Asking for Confirmation During Operations
@cindex Interactive operation
The basic @command{tar} operations, @option{--create} (@option{-c}),
@option{--list} (@option{-t}) and @option{--extract} (@option{--get},
-@option{-x}), are currently presented and described in the tutorial
+@option{-x}), are currently presented and described in the tutorial
chapter of this manual. This section provides some complementary notes
for these operations.
@table @option
-@opindex create, complementary notes
+@xopindex{create, complementary notes}
@item --create
@itemx -c
file, which was meant to be saved, is rather destroyed.
@end enumerate
-So, recognizing the likelihood and the catastrophical nature of these
+So, recognizing the likelihood and the catastrophic nature of these
errors, @GNUTAR{} now takes some distance from elegance, and
cowardly refuses to create an archive when @option{--create} option is
given, there are no arguments besides options, and
around the cautiousness of @GNUTAR{} and nevertheless create an
archive with nothing in it, one may still use, as the value for the
@option{--files-from} option, a file with no names in it, as shown in
-the following commands:
+the following commands:
@smallexample
@kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
@kbd{tar cfT empty-archive.tar /dev/null}
@end smallexample
-@opindex extract, complementary notes
+@xopindex{extract, complementary notes}
@item --extract
@itemx --get
@itemx -x
ready. In the meantime, programs not being localizable for dates
should prefer international dates, that's really the way to go.
-Look up @url{http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html} if you
+Look up @url{http://www.cl.cam.ac.uk/@/~mgk25/@/iso-time.html} if you
are curious, it contains a detailed explanation of the ISO 8601 standard.
@end table
@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{bfiles.tar}. The archive @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
@noindent
would extract only the second copy. @xref{Option
Summary,---occurrence}, for the description of @option{--occurrence}
-option.
+option.
@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...
@cindex Archives, Appending files to
The simplest way to add a file to an already existing archive is the
-@option{--append} (@option{-r}) operation, which writes specified files into the
-archive whether or not they are already among the archived files.
+@option{--append} (@option{-r}) operation, which writes specified
+files into the archive whether or not they are already among the
+archived files.
+
When you use @option{--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
-rw-r--r-- me user 20 1996-09-23 16:44 rock
@end smallexample
-@FIXME{in theory, dan will (soon) try to turn this node into what it's
-title claims it will become...}
-
@node multiple
-@subsubsection Multiple Files with the Same Name
-
-You can use @option{--append} (@option{-r}) 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 @command{tar} option called
-@option{--update}; @pxref{update} for more information. We describe this
-use of @option{--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 we 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
+@subsubsection Multiple Members with the Same Name
+
+You can use @option{--append} (@option{-r}) 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 @command{tar}
+option called @option{--update}; @xref{update}, for more information.
+We describe this use of @option{--append} here for the sake of
+completeness.) 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 replace 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.
+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
@opindex update
In the previous section, you learned how to use @option{--append} to
-add a file to an existing archive. A related operation is
+add a file to an existing archive. A related operation is
@option{--update} (@option{-u}). The @option{--update} operation
updates a @command{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
-@option{--append}).
+@option{--append}).
Unfortunately, you cannot use @option{--update} with magnetic tape drives.
The operation will fail.
Both @option{--update} and @option{--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 @option{--backup} option. @FIXME-ref{Multiple Members with the
-Same Name}
+the @option{--backup} option. @xref{multiple}, for a detailed discussion.
@menu
* how to update::
@node how to update
@subsubsection How to Update an Archive Using @option{--update}
-You must use file name arguments with the @option{--update} (@option{-u}) operation.
-If you don't specify any files, @command{tar} won't act on any files and
-won't tell you that it didn't do anything (which may end up confusing
-you).
+You must use file name arguments with the @option{--update}
+(@option{-u}) operation. If you don't specify any files,
+@command{tar} won't act on any files and won't tell you that it didn't
+do anything (which may end up confusing you).
-@FIXME{note: the above parenthetical added because in fact, this
-behavior just confused the author. :-) }
+@c note: the above parenthetical added because in fact, this
+@c behavior just confused the author. :-)
To see the @option{--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 @command{tar} with
-the @samp{update} operation and the @option{--verbose} (@option{-v}) option specified,
-using the names of all the files in the practice directory as file name
-arguments:
+the @samp{update} operation and the @option{--verbose} (@option{-v})
+option specified, using the names of all the files in the practice
+directory as file name arguments:
@smallexample
$ @kbd{tar --update -v -f collection.tar blues folk rock classical}
@option{--file} option and name the rest of archives to be
concatenated on the command line. The members, and their member
names, will be copied verbatim from those archives to the first one.
-@FIXME-ref{This can cause multiple members to have the same name, for
-information on how this affects reading the archive, Multiple
-Members with the Same Name.}
+@footnote{This can cause multiple members to have the same name, for
+information on how this affects reading the archive, @ref{multiple}.}
The new, concatenated archive will be called by the same name as the
one given with the @option{--file} option. As usual, if you omit
@option{--file}, @command{tar} will use the value of the environment
@smallexample
$ @kbd{tar -cvf bluesrock.tar blues rock}
blues
-classical
+rock
$ @kbd{tar -cvf folkjazz.tar folk jazz}
folk
jazz
$ @kbd{tar -tvf bluesrock.tar}
-rw-r--r-- melissa user 105 1997-01-21 19:42 blues
-rw-r--r-- melissa user 33 1997-01-20 15:34 rock
-$ @kbd{tar -tvf folkjazz.tar}
+$ @kbd{tar -tvf jazzfolk.tar}
-rw-r--r-- melissa user 20 1996-09-23 16:44 folk
-rw-r--r-- melissa user 65 1997-01-30 14:15 jazz
@end smallexample
-We can concatenate these two archives with @command{tar}:
+We can concatenate these two archives with @command{tar}:
@smallexample
$ @kbd{cd ..}
$ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
@end smallexample
-If you now list the contents of the @file{bluesclass.tar}, you will see
+If you now list the contents of the @file{bluesrock.tar}, you will see
that now it also contains the archive members of @file{jazzfolk.tar}:
@smallexample
$ @kbd{tar --list --file=bluesrock.tar}
blues
rock
-jazz
folk
+jazz
@end smallexample
When you use @option{--concatenate}, the source and target archives must
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
$
@end smallexample
-@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!}
+@FIXME{Check if the above listing is actually produced after running
+all the examples on collection.tar.}
The @option{--delete} option has been reported to work properly when
@command{tar} acts as a filter from @code{stdin} to @code{stdout}.
tar: funk not found in archive
@end smallexample
-The spirit behind the @option{--compare} (@option{--diff}, @option{-d}) 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}.
+The spirit behind the @option{--compare} (@option{--diff},
+@option{-d}) 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 create options
@section Options Used by @option{--create}
-@opindex create, additional options
+@xopindex{create, additional options}
The previous chapter described the basics of how to use
@option{--create} (@option{-c}) to create an archive from a set of files.
@xref{create}. This section described advanced options to be used with
@option{--create}.
@menu
+* override:: Overriding File Metadata.
* Ignore Failed Read::
@end menu
+@node override
+@subsection Overriding File Metadata
+
+As described above, a @command{tar} archive keeps, for each member it contains,
+its @dfn{metadata}, such as modification time, mode and ownership of
+the file. @GNUTAR{} allows to replace these data with other values
+when adding files to the archive. The options described in this
+section affect creation of archives of any type. For POSIX archives,
+see also @ref{PAX keywords}, for additional ways of controlling
+metadata, stored in the archive.
+
+@table @option
+@opindex mode
+@item --mode=@var{permissions}
+
+When adding files to an archive, @command{tar} will use
+@var{permissions} for the archive members, rather than the permissions
+from the files. @var{permissions} can be specified either as an octal
+number or as symbolic permissions, like with
+@command{chmod} (@xref{File permissions, Permissions, File
+permissions, fileutils, @acronym{GNU} file utilities}. This reference
+also has useful information for those not being overly familiar with
+the UNIX permission system). Using latter syntax allows for
+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:
+
+@smallexample
+$ @kbd{tar -c -f archive.tar --mode='a+rw' .}
+@end smallexample
+
+@item --mtime=@var{date}
+@opindex mtime
+
+When adding files to an archive, @command{tar} will use @var{date} as
+the modification time of members when creating archives, instead of
+their actual modification times. The argument @var{date} can be
+either a textual date representation in almost arbitrary format
+(@pxref{Date input formats}) or a name of the existing file, starting
+with @samp{/} or @samp{.}. In the latter case, the modification time
+of that file will be used.
+
+The following example will set the modification date to 00:00:00 UTC,
+January 1, 1970:
+
+@smallexample
+$ @kbd{tar -c -f archive.tar --mtime='1970-01-01' .}
+@end smallexample
+
+@noindent
+When used with @option{--verbose} (@pxref{verbose tutorial}) @GNUTAR{}
+will try to convert the specified date back to its textual
+representation and compare it with the one given with
+@option{--mtime} options. If the two dates differ, @command{tar} will
+print a warning saying what date it will use. This is to help user
+ensure he is using the right date.
+
+For example:
+
+@smallexample
+$ @kbd{tar -c -f archive.tar -v --mtime=yesterday .}
+tar: Option --mtime: Treating date `yesterday' as 2006-06-20
+13:06:29.152478
+@dots{}
+@end smallexample
+
+@item --owner=@var{user}
+@opindex owner
+
+Specifies that @command{tar} should use @var{user} as the owner of members
+when creating archives, instead of the user associated with the source
+file. The argument @var{user} can be either an existing user symbolic
+name, or a decimal numeric user @acronym{ID}.
+
+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. For example:
+
+@smallexample
+@group
+$ @kbd{tar -c -f archive.tar --owner=0 .}
+# @r{Or:}
+$ @kbd{tar -c -f archive.tar --owner=root .}
+@end group
+@end smallexample
+
+@item --group=@var{group}
+@opindex group
+
+Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
+rather than the group from the source file. The argument @var{group}
+can be either an existing group symbolic name, or a decimal numeric group @acronym{ID}.
+@end table
+
@node Ignore Failed Read
@subsection Ignore Fail Read
@table @option
@item --ignore-failed-read
+@opindex ignore-failed-read
Do not exit with nonzero on unreadable files or directories.
@end table
@section Options Used by @option{--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.}
-
-@opindex extract, additional options
+@xopindex{extract, additional options}
The previous chapter showed how to use @option{--extract} to extract
an archive into the file system. Various options cause @command{tar} to
extract more information than just file contents, such as the owner,
The @option{--read-full-records} (@option{-B}) option is turned on by default when
@command{tar} reads an archive from standard input, or from a remote
-machine. This is because on BSD Unix systems, attempting to read a
+machine. This is because on @acronym{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, @command{tar}
would fail as soon as it read an incomplete record from the pipe.
read the archive by specifying @option{--read-full-records} (@option{-B}) and
@option{--blocking-factor=@var{512-size}} (@option{-b
@var{512-size}}), using a blocking factor larger than what the archive
-uses. This lets you avoid having to determine the blocking factor
+uses. This lets you avoid having to determine the blocking factor
of an archive. @xref{Blocking Factor}.
@menu
versions of @command{tar} write garbage after the end-of-archive entry,
since that part of the media is never supposed to be read. @GNUTAR{}
does not write after the end of an archive, but seeks to
-maintain compatiblity among archiving utilities.
+maintain compatibility among archiving utilities.
@table @option
@item --ignore-zeros
* Recursive Unlink::
* Data Modification Times::
* Setting Access Permissions::
+* Directory Modification Times and Permissions::
* Writing to Standard Output::
* Writing to an External Program::
* remove files::
@node Dealing with Old Files
@unnumberedsubsubsec Options Controlling the Overwriting of Existing Files
-@opindex overwrite-dir, introduced
+@xopindex{overwrite-dir, introduced}
When extracting files, if @command{tar} discovers that the extracted
file already exists, it normally replaces the file by removing it before
extracting it, to prevent confusion in the presence of hard or symbolic
such a directory, use the @option{--no-overwrite-dir} option.
@cindex Overwriting old files, prevention
-@opindex keep-old-files, introduced
+@xopindex{keep-old-files, introduced}
To be even more cautious and prevent existing files from being replaced, use
the @option{--keep-old-files} (@option{-k}) option. It causes @command{tar} to refuse
to replace or update a file that already exists, i.e., a file with the
same name as an archive member prevents extraction of that archive
member. Instead, it reports an error.
-@opindex overwrite, introduced
+@xopindex{overwrite, introduced}
To be more aggressive about altering existing files, use the
@option{--overwrite} option. It causes @command{tar} to overwrite
existing files and to follow existing symbolic links when extracting.
to allow this behavior. In any case, single files are silently
removed.
-@opindex unlink-first, introduced
+@xopindex{unlink-first, introduced}
Finally, the @option{--unlink-first} (@option{-U}) option can improve performance in
some cases by causing @command{tar} to remove files unconditionally
before extracting them.
conjunction with @option{--extract} (@option{--get}, @option{-x}).
@table @option
-@opindex touch
+@opindex touch
@item --touch
@itemx -m
Sets the data modification time of extracted archive members to the time
To set the modes (access permissions) of extracted files to those
recorded for those files in the archive, use @option{--same-permissions}
in conjunction with the @option{--extract} (@option{--get},
-@option{-x}) operation. @FIXME{Should be aliased to ignore-umask.}
+@option{-x}) operation.
@table @option
-@opindex preserve-permission
-@opindex same-permission
-@item --preserve-permission
-@itemx --same-permission
+@opindex preserve-permissions
+@opindex same-permissions
+@item --preserve-permissions
+@itemx --same-permissions
@c @itemx --ignore-umask
@itemx -p
Set modes of extracted archive members to those recorded in the
@option{--extract} (@option{--get}, @option{-x}).
@end table
+@node Directory Modification Times and Permissions
+@unnumberedsubsubsec Directory Modification Times and Permissions
+
+After successfully extracting a file member, @GNUTAR{} normally
+restores its permissions and modification times, as described in the
+previous sections. This cannot be done for directories, because
+after extracting a directory @command{tar} will almost certainly
+extract files into that directory and this will cause the directory
+modification time to be updated. Moreover, restoring that directory
+permissions may not permit file creation within it. Thus, restoring
+directory permissions and modification times must be delayed at least
+until all files have been extracted into that directory. @GNUTAR{}
+restores directories using the following approach.
+
+The extracted directories are created with the mode specified in the
+archive, as modified by the umask of the user, which gives sufficient
+permissions to allow file creation. The meta-information about the
+directory is recorded in the temporary list of directories. When
+preparing to extract next archive member, @GNUTAR{} checks if the
+directory prefix of this file contains the remembered directory. If
+it does not, the program assumes that all files have been extracted
+into that directory, restores its modification time and permissions
+and removes its entry from the internal list. This approach allows
+to correctly restore directory meta-information in the majority of
+cases, while keeping memory requirements sufficiently small. It is
+based on the fact, that most @command{tar} archives use the predefined
+order of members: first the directory, then all the files and
+subdirectories in that directory.
+
+However, this is not always true. The most important exception are
+incremental archives (@pxref{Incremental Dumps}). The member order in
+an incremental archive is reversed: first all directory members are
+stored, followed by other (non-directory) members. So, when extracting
+from incremental archives, @GNUTAR{} alters the above procedure. It
+remembers all restored directories, and restores their meta-data
+only after the entire archive has been processed. Notice, that you do
+not need to specify any special options for that, as @GNUTAR{}
+automatically detects archives in incremental format.
+
+There may be cases, when such processing is required for normal archives
+too. Consider the following example:
+
+@smallexample
+@group
+$ @kbd{tar --no-recursion -cvf archive \
+ foo foo/file1 bar bar/file foo/file2}
+foo/
+foo/file1
+bar/
+bar/file
+foo/file2
+@end group
+@end smallexample
+
+During the normal operation, after encountering @file{bar}
+@GNUTAR{} will assume that all files from the directory @file{foo}
+were already extracted and will therefore restore its timestamp and
+permission bits. However, after extracting @file{foo/file2} the
+directory timestamp will be offset again.
+
+To correctly restore directory meta-information in such cases, use
+@option{delay-directory-restore} command line option:
+
+@table @option
+@opindex delay-directory-restore
+@item --delay-directory-restore
+Delays restoring of the modification times and permissions of extracted
+directories until the end of extraction. This way, correct
+meta-information is restored even if the archive has unusual member
+ordering.
+
+@opindex no-delay-directory-restore
+@item --no-delay-directory-restore
+Cancel the effect of the previous @option{--delay-directory-restore}.
+Use this option if you have used @option{--delay-directory-restore} in
+@env{TAR_OPTIONS} variable (@pxref{TAR_OPTIONS}) and wish to
+temporarily disable it.
+@end table
+
@node Writing to Standard Output
@unnumberedsubsubsec Writing to Standard Output
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 @option{--list}
-(@option{-t}).
+(@option{-t}).
@end table
This can be useful, for example, if you have a tar archive containing
tar -xOzf foo.tgz bigfile1 bigfile2 | process
@end smallexample
-Hovewer, @option{--to-command} may be more convenient for use with
+However, @option{--to-command} may be more convenient for use with
multiple files. See the next section.
@node Writing to an External Program
file to the standard input of an external program:
@table @option
-@opindex to-program
-@item --to-program=@var{command}
+@opindex to-command
+@item --to-command=@var{command}
Extract files and pipe their contents to the standard input of
@var{command}. When this option is used, instead of creating the
files specified, @command{tar} invokes @var{command} and pipes the
The command can obtain the information about the file it processes
from the following environment variables:
-@table @var
+@table @env
@vrindex TAR_FILETYPE, to-command environment
@item TAR_FILETYPE
Type of the file. It is a single letter with the following meaning:
@node remove files
@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...}
+@FIXME{The section is too terse. Something more to add? An example,
+maybe?}
@table @option
@opindex remove-files
To process large lists of file names on machines with small amounts of
memory. Use in conjunction with @option{--compare} (@option{--diff},
@option{-d}), @option{--list} (@option{-t}) or @option{--extract}
-(@option{--get}, @option{-x}).
+(@option{--get}, @option{-x}).
@end table
The @option{--same-order} (@option{--preserve-order}, @option{-s}) option tells @command{tar} that the list of file
@end table
-Some people express the desire to @emph{always} use the @option{--backup}
-option, by defining some kind of alias or script. This is not as easy
-as one may think, due to the fact that old style options should appear first
-and consume arguments a bit unpredictably 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):
-
-@smallexample
-tar () @{ /usr/local/bin/tar --backup $*; @}
-@end smallexample
-
@node Applications
@section Notable @command{tar} Usages
@UNREVISED
medium is a @dfn{pipe}, which is one a Unix redirection mechanism:
@smallexample
-$ @kbd{cd sourcedir; tar -cf - . | (cd targetdir; tar -xf -)}
+$ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)}
@end smallexample
@noindent
-The command also works using short option forms:
+You can avoid subshells by using @option{-C} option:
@smallexample
-$ @w{@kbd{cd sourcedir; tar --create --file=- . | (cd targetdir; tar --extract --file=-)}}
+$ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xf -}
@end smallexample
@noindent
-This is one of the easiest methods to transfer a @command{tar} archive.
+The command also works using short option forms:
+
+@smallexample
+$ @kbd{(cd sourcedir; tar --create --file=- . ) \
+ | (cd targetdir; tar --extract --file=-)}
+# Or:
+$ @kbd{tar --directory sourcedir --create --file=- . ) \
+ | tar --directory targetdir --extract --file=-}
+@end smallexample
+
+@noindent
+This is one of the easiest methods to transfer a @command{tar} archive.
@node looking ahead
@section Looking Ahead: The Rest of this Manual
not corrupt the entire archive.)
You will want to use the @option{--label=@var{archive-label}}
-(@option{-V @var{archive-label}}) option to give the archive a
+(@option{-V @var{archive-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.
Make sure you have enough tapes on hand to complete the backup.
If you want to dump each file system separately you will need to use
-the @option{--one-file-system} (@option{-l}) option to prevent
+the @option{--one-file-system} option to prevent
@command{tar} from crossing file system boundaries when storing
-(sub)directories.
+(sub)directories.
The @option{--incremental} (@option{-G}) (@pxref{Incremental Dumps})
option is not needed, since this is a complete copy of everything in
the file system, and a full restore from this backup would only be
-done onto a completely
+done onto a completely
empty disk.
Unless you are in a hurry, and trust the @command{tar} program (and your
@GNUTAR{} currently offers two options for handling incremental
backups: @option{--listed-incremental=@var{snapshot-file}} (@option{-g
-@var{snapshot-file}}) and @option{--incremental} (@option{-G}).
+@var{snapshot-file}}) and @option{--incremental} (@option{-G}).
@opindex listed-incremental
The option @option{--listed-incremental} instructs tar to operate on
with the @option{--atime-preserve=replace} option), or if you set the clock
backwards.
+@anchor{device numbers}
+@cindex Device numbers, using in incremental backups
Metadata stored in snapshot files include device numbers, which,
-obviously is supposed to be a non-volatile value. However, it turns
-out that NFS devices have undependable values when an automounter
+obviously are supposed to be a non-volatile values. However, it turns
+out that @acronym{NFS} devices have undependable values when an automounter
gets in the picture. This can lead to a great deal of spurious
redumping in incremental dumps, so it is somewhat useless to compare
-two NFS devices numbers over time. The solution implemented currently
-is to 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.
+two @acronym{NFS} devices numbers over time. The solution implemented
+currently is to considers all @acronym{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.
+
+Apart from using @acronym{NFS}, there are a number of cases where
+relying on device numbers can cause spurious redumping of unmodified
+files. For example, this occurs when archiving @acronym{LVM} snapshot
+volumes. To avoid this, use @option{--no-check-device} option:
+
+@table @option
+@xopindex{no-check-device, described}
+@item --no-check-device
+Do not rely on device numbers when preparing a list of changed files
+for an incremental dump.
+
+@xopindex{check-device, described}
+@item --check-device
+Use device numbers when preparing a list of changed files
+for an incremental dump. This is the default behavior. The purpose
+of this option is to undo the effect of the @option{--no-check-device}
+if it was given in @env{TAR_OPTIONS} environment variable
+(@pxref{TAR_OPTIONS}).
+@end table
+
+There is also another way to cope with changing device numbers. It is
+described in detail in @ref{Fixing Snapshot Files}.
Note that incremental archives use @command{tar} extensions and may
not be readable by non-@acronym{GNU} versions of the @command{tar} program.
-@opindex listed-incremental, using with @option{--extract}
-@opindex extract, using with @option{--listed-incremental}
+@xopindex{listed-incremental, using with @option{--extract}}
+@xopindex{extract, using with @option{--listed-incremental}}
To extract from the incremental dumps, use
@option{--listed-incremental} together with @option{--extract}
option (@pxref{extracting files}). In this case, @command{tar} does
the last level was created, you will need to restore from all backups
in turn. Continuing our example, to restore the state of @file{/usr}
file system, one would do@footnote{Notice, that since both archives
-were created withouth @option{-P} option (@pxref{absolute}), these
+were created without @option{-P} option (@pxref{absolute}), these
commands should be run from the root file system.}:
@smallexample
verbose listing output (@option{--list --verbose}) when using in
scripts.
-@opindex incremental, using with @option{--list}
-@opindex listed-incremental, using with @option{--list}
-@opindex list, using with @option{--incremental}
-@opindex list, using with @option{--listed-incremental}
+@xopindex{incremental, using with @option{--list}}
+@xopindex{listed-incremental, using with @option{--list}}
+@xopindex{list, using with @option{--incremental}}
+@xopindex{list, using with @option{--listed-incremental}}
Versions of @GNUTAR{} up to 1.15.1 used to dump verbatim binary
contents of the DUMPDIR header (with terminating nulls) when
@option{--incremental} or @option{--listed-incremental} option was
given, no matter what the verbosity level. This behavior, and,
-especially, the binary output it produced were considered incovenient
+especially, the binary output it produced were considered inconvenient
and were changed in version 1.16}:
@smallexample
where @var{x} is a letter describing the status of the file: @samp{Y}
if the file is present in the archive, @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).@FIXME-xref{dumpdir format}. Each such
+is included in the archive). @xref{Dumpdir}, for the detailed
+description of dumpdirs and status codes. Each such
line is terminated by a newline character. The last line is followed
by an additional newline to indicate the end of the data.
the host machine must have @GNUTAR{} 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 @command{pwd} will print
+machine where the scripts are run (i.e., what @command{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.
+host as long as it can access the file system through @acronym{NFS}.
If the list of file systems is very long you may wish to put it
in a separate file. This file is usually named
@defvr {Backup variable} DIRLIST
-A path to the file containing the list of the file systems to backup
+The name of the file that contains a list of file systems to backup
or restore. By default it is @file{/etc/backup/dirs}.
@end defvr
@defvr {Backup variable} FILELIST
-A path to the file containing the list of the individual files to backup
+The name of the file that contains a list of individual files to backup
or restore. By default it is @file{/etc/backup/files}.
@end defvr
@defvr {Backup variable} RSH_COMMAND
-Full file name of @command{rsh} binary on remote mashines. This will
+Full file name of @command{rsh} binary on remote machines. This will
be passed via @option{--rsh-command} option to the remote invocation
of @GNUTAR{}.
@end defvr
Script to be run when it's time to insert a new tape in for the next
volume. Administrators may want to tailor this script for their site.
-If this variable isn't set, @GNUTAR{} will display its built-in prompt
-@FIXME-xref{describe it somewhere!}, and will expect confirmation from
-the console.
+If this variable isn't set, @GNUTAR{} will display its built-in
+prompt, and will expect confirmation from the console. For the
+description of the default prompt, see @ref{change volume prompt}.
+
@end defvr
@defvr {Backup variable} SLEEP_MESSAGE
Name or IP address of the host machine being dumped or restored.
@item fs
-Full path name to the file system being dumped or restored.
+Full file name of the file system being dumped or restored.
@item fsname
File system name with directory separators replaced with colons. This
@item -v[@var{level}]
@itemx --verbose[=@var{level}]
Set verbosity level. The higher the level is, the more debugging
-information will be output during execution. Devault @var{level}
+information will be output during execution. Default @var{level}
is 100, which means the highest debugging level.
@item -t @var{start-time}
@itemx --help
Display short help message and exit.
-@item -L
-@itemx --license
-Display program license and exit.
-
@item -V
@itemx --version
-Display program version and exit.
+Display information about the program's name, version, origin and legal
+status, all on standard output, and then exit successfully.
@end table
@item -v[@var{level}]
@itemx --verbose[=@var{level}]
Set verbosity level. The higher the level is, the more debugging
-information will be output during execution. Devault @var{level}
+information will be output during execution. Default @var{level}
is 100, which means the highest debugging level.
@item -h
@itemx --help
Display short help message and exit.
-@item -L
-@itemx --license
-Display program license and exit.
-
@item -V
@itemx --version
-Display program version and exit.
+Display information about the program's name, version, origin and legal
+status, all on standard output, and then exit successfully.
@end table
You should start the restore script with the media containing the
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.}
+the tape as needed. @xref{Tape Positioning}, for a discussion of tape
+positioning.
@quotation
@strong{Warning:} The script will delete files from the active file
@chapter Choosing Files and Names for @command{tar}
@UNREVISED
-@FIXME{Melissa (still) Doesn't Really Like This ``Intro'' Paragraph!!!}
-
Certain options to @command{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.
+This chapter discusses these options in detail.
+
@menu
* file:: Choosing the Archive's Name
* Selecting Archive Members::
* files:: Reading Names from a File
* exclude:: Excluding Some Files
-* Wildcards::
+* wildcards:: Wildcards Patterns and Matching
+* quoting styles:: Ways of Quoting Special Characters in Names
+* transform:: Modifying File and Member Names
* after:: Operating Only on New Files
* recurse:: Descending into Directories
* one:: Crossing File System Boundaries
@section Choosing and Naming Archive Files
@UNREVISED
-@FIXME{should the title of this section actually be, "naming an
-archive"?}
-
@cindex Naming an archive
@cindex Archive Name
@cindex Choosing an archive file
By default, @command{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 @command{tar}
-on the system may not set the default to a meaningful value as far as
+on the system may not have set the default to a meaningful value as far as
most users are concerned. As a result, you will usually want to tell
-@command{tar} where to find (or create) the archive. The @option{--file=@var{archive-name}} (@option{-f @var{archive-name}})
+@command{tar} where to find (or create) the archive. The
+@option{--file=@var{archive-name}} (@option{-f @var{archive-name}})
option allows you to either specify or name a file to use as the archive
instead of the default archive file location.
@table @option
-@opindex file, short description
+@xopindex{file, short description}
@item --file=@var{archive-name}
@itemx -f @var{archive-name}
Name the archive to create or operate on. Use in conjunction with
If you do not name the archive, @command{tar} uses the value of the
environment variable @env{TAPE} as the file name for the archive. If
that is not available, @command{tar} uses a default, compiled-in archive
-name, usually that for tape unit zero (ie. @file{/dev/tu00}).
-@command{tar} always needs an archive name.
+name, usually that for tape unit zero (i.e., @file{/dev/tu00}).
+@cindex Standard input and output
+@cindex tar to standard input and output
If you use @file{-} as an @var{archive-name}, @command{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
@command{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".}
+The following example is a convenient way of copying directory
+hierarchy from @file{sourcedir} to @file{targetdir}.
@smallexample
-$ @kbd{cd sourcedir; tar -cf - . | (cd targetdir; tar -xf -)}
+$ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)}
@end smallexample
-@FIXME{help!}
+The @option{-C} option allows to avoid using subshells:
-@cindex Standard input and output
-@cindex tar to standard input and output
+@smallexample
+$ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xpf -}
+@end smallexample
+
+In both examples above, the leftmost @command{tar} invocation archives
+the contents of @file{sourcedir} to the standard output, while the
+rightmost one reads this archive from its standard input and
+extracts it. The @option{-p} option tells it to restore permissions
+of the extracted files.
+
+@cindex Remote devices
+@cindex tar to a remote device
@anchor{remote-dev}
To specify an archive file on a device attached to a remote machine,
use the following:
@smallexample
-@kbd{--file=@var{hostname}:/@var{dev}/@var{file name}}
+@kbd{--file=@var{hostname}:/@var{dev}/@var{file-name}}
@end smallexample
@noindent
@command{tar} will complete the remote connection, if possible, and
prompt you for a username and password. If you use
-@option{--file=@@@var{hostname}:/@var{dev}/@var{file name}}, @command{tar}
+@option{--file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @command{tar}
will complete the remote connection, if possible, using your username
as the username on the remote machine.
colon, then the remote tape drive behavior
can be inhibited by using the @option{--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}, @GNUTAR{}
-tries to minimize input and output operations. The
-Amanda backup system, when used with @GNUTAR{}, has
-an initial sizing pass which uses this feature.
+tries to minimize input and output operations. The Amanda backup
+system, when used with @GNUTAR{}, has an initial sizing pass which
+uses this feature.
@node Selecting Archive Members
@section Selecting Archive Members
@kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}]
@end smallexample
-If a file name begins with dash (@samp{-}), preceede it with
-@option{--add-file} option to preventit from being treated as an
+If a file name begins with dash (@samp{-}), precede it with
+@option{--add-file} option to prevent it from being treated as an
option.
+@anchor{input name quoting}
+By default @GNUTAR{} attempts to @dfn{unquote} each file or member
+name, replacing @dfn{escape sequences} according to the following
+table:
+
+@multitable @columnfractions 0.20 0.60
+@headitem Escape @tab Replaced with
+@item \a @tab Audible bell (@acronym{ASCII} 7)
+@item \b @tab Backspace (@acronym{ASCII} 8)
+@item \f @tab Form feed (@acronym{ASCII} 12)
+@item \n @tab New line (@acronym{ASCII} 10)
+@item \r @tab Carriage return (@acronym{ASCII} 13)
+@item \t @tab Horizontal tabulation (@acronym{ASCII} 9)
+@item \v @tab Vertical tabulation (@acronym{ASCII} 11)
+@item \? @tab @acronym{ASCII} 127
+@item \@var{n} @tab @acronym{ASCII} @var{n} (@var{n} should be an octal number
+ of up to 3 digits)
+@end multitable
+
+A backslash followed by any other symbol is retained.
+
+This default behavior is controlled by the following command line
+option:
+
+@table @option
+@opindex unquote
+@item --unquote
+Enable unquoting input file or member names (default).
+
+@opindex no-unquote
+@item --no-unquote
+Disable unquoting input file or member names.
+@end table
+
If you specify a directory name as a file name argument, all the files
in that directory are operated on by @command{tar}.
-If you do not specify files when @command{tar} is invoked with
-@option{--create} (@option{-c}), @command{tar} operates on all the non-directory files in
-the working directory. If you specify either @option{--list} (@option{-t}) or
-@option{--extract} (@option{--get}, @option{-x}), @command{tar} operates on all the archive members in the
-archive. If you specify any operation other than one of these three,
-@command{tar} does nothing.
+If you do not specify files, @command{tar} behavior differs depending
+on the operation mode as described below:
+
+When @command{tar} is invoked with @option{--create} (@option{-c}),
+@command{tar} will stop immediately, reporting the following:
+
+@smallexample
+@group
+$ @kbd{tar cf a.tar}
+tar: Cowardly refusing to create an empty archive
+Try `tar --help' or `tar --usage' for more information.
+@end group
+@end smallexample
+
+If you specify either @option{--list} (@option{-t}) or
+@option{--extract} (@option{--get}, @option{-x}), @command{tar}
+operates on all the archive members in the archive.
+
+If run with @option{--diff} option, tar will compare the archive with
+the contents of the current working directory.
+
+If you specify any other operation, @command{tar} does nothing.
By default, @command{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 @command{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.
+operate. In general, these methods work both for specifying the names
+of files and archive members.
@node files
@section Reading Names from a File
@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
-@option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) option to @command{tar}. Give the name of the file
-which contains the list of files to include as the argument to
+@option{--files-from=@var{file-of-names}} (@option{-T
+@var{file-of-names}}) option to @command{tar}. Give the name of the
+file which contains the list of files to include as the argument to
@option{--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 @command{find} utility.
@table @option
@opindex files-from
-@item --files-from=@var{file name}
-@itemx -T @var{file name}
-Get names to extract or create from file @var{file name}.
+@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 @option{--files-from}, (i.e.,
Any number of @option{-T} options can be given in the command line.
-@FIXME{add bob's example, from his message on 2-10-97}
-
The following example shows how to use @command{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 @option{-T} option to
@end smallexample
@noindent
-@opindex directory, using in @option{--files-from} argument
+@xopindex{directory, using in @option{--files-from} argument}
Notice that the option parsing algorithm used with @option{-T} is
stricter than the one used by shell. Namely, when specifying option
arguments, you should observe the following rules:
@opindex add-file
If you happen to have a file whose name starts with @samp{-},
precede it with @option{--add-file} option to prevent it from
-being recognized as an option. For example: @code{--add-file --my-file}.
+being recognized as an option. For example: @code{--add-file=--my-file}.
@menu
* nul::
@cindex File names, terminated by @code{NUL}
@cindex @code{NUL} terminated file names
-The @option{--null} option causes @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) to read file
-names terminated by a @code{NUL} instead of a newline, so files whose
-names contain newlines can be archived using @option{--files-from}.
+The @option{--null} option causes
+@option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}})
+to read file names terminated by a @code{NUL} instead of a newline, so
+files whose names contain newlines can be archived using
+@option{--files-from}.
@table @option
-@opindex null
+@xopindex{null, described}
@item --null
Only consider @code{NUL} terminated file names, instead of files that
terminate in a newline.
+
+@xopindex{no-null, described}
+@item --no-null
+Undo the effect of any previous @option{--null} option.
@end table
The @option{--null} option is just like the one in @acronym{GNU}
$ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
@end smallexample
-@FIXME{say anything else here to conclude the section?}
+The @option{--no-null} option can be used if you need to read both
+zero-terminated and newline-terminated files on the same command line.
+For example, if @file{flist} is a newline-terminated file, then the
+following command can be used to combine it with the above command:
+
+@smallexample
+@group
+$ @kbd{find . -size +800 -print0 |
+ tar -c -f big.tar --null -T - --no-null -T flist}
+@end group
+@end smallexample
+
+This example uses short options for typographic reasons, to avoid
+very long lines.
+
+@GNUTAR is able to automatically detect null-terminated file lists, so
+it is safe to use them even without the @option{--null} option. In
+this case @command{tar} will print a warning and continue reading such
+a file as if @option{--null} were actually given:
+
+@smallexample
+@group
+$ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -}
+tar: -: file name read contains nul character
+@end group
+@end smallexample
+
+The null terminator, however, remains in effect only for this
+particular file, any following @option{-T} options will assume
+newline termination. Of course, the null autodetection applies
+to these eventual surplus @option{-T} options as well.
@node exclude
@section Excluding Some Files
@cindex Excluding files by name and pattern
@cindex Excluding files by file system
To avoid operating on files whose names match a particular pattern,
-use the @option{--exclude} or @option{--exclude-from} options.
+use the @option{--exclude} or @option{--exclude-from} options.
@table @option
@opindex exclude
@end table
@findex exclude
-The @option{--exclude=@var{pattern}} option prevents any file or member whose name
-matches the shell wildcard (@var{pattern}) from being operated on.
+The @option{--exclude=@var{pattern}} option prevents any file or
+member whose name matches the shell wildcard (@var{pattern}) from
+being operated on.
For example, to create an archive with all the contents of the directory
@file{src} except for files whose names end in @file{.o}, use the
command @samp{tar -cf src.tar --exclude='*.o' src}.
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?}
-
+Notice, that lines from @var{file} are read verbatim. One of the
+frequent errors is leaving some extra whitespace after a file name,
+which is difficult to catch using text editors.
+
+However, empty lines are OK.
+
+@cindex version control system, excluding files
+@cindex VCS, excluding files
+@cindex SCCS, excluding files
+@cindex RCS, excluding files
+@cindex CVS, excluding files
+@cindex SVN, excluding files
+@cindex git, excluding files
+@cindex Bazaar, excluding files
+@cindex Arch, excluding files
+@cindex Mercurial, excluding files
+@cindex Darcs, excluding files
@table @option
-@opindex exclude-caches
-@item --exclude-caches
-Causes @command{tar} to ignore directories containing a cache directory tag.
+@opindex exclude-vcs
+@item --exclude-vcs
+Exclude files and directories used by following version control
+systems: @samp{CVS}, @samp{RCS}, @samp{SCCS}, @samp{SVN}, @samp{Arch},
+@samp{Bazaar}, @samp{Mercurial}, and @samp{Darcs}.
@end table
+As of version @value{VERSION}, the following files are excluded:
+
+@itemize @bullet
+@item @file{CVS/}, and everything under it
+@item @file{RCS/}, and everything under it
+@item @file{SCCS/}, and everything under it
+@item @file{.git/}, and everything under it
+@item @file{.gitignore}
+@item @file{.cvsignore}
+@item @file{.svn/}, and everything under it
+@item @file{.arch-ids/}, and everything under it
+@item @file{@{arch@}/}, and everything under it
+@item @file{=RELEASE-ID}
+@item @file{=meta-update}
+@item @file{=update}
+@item @file{.bzr}
+@item @file{.bzrignore}
+@item @file{.bzrtags}
+@item @file{.hg}
+@item @file{.hgignore}
+@item @file{.hgrags}
+@item @file{_darcs}
+@end itemize
+
@findex exclude-caches
-When creating an archive, the @option{--exclude-caches} option causes
-@command{tar} to exclude all directories that contain a @dfn{cache
+When creating an archive, the @option{--exclude-caches} option family
+causes @command{tar} to exclude all directories that contain a @dfn{cache
directory tag}. A cache directory tag is a short file with the
well-known name @file{CACHEDIR.TAG} and having a standard header
specified in @url{http://www.brynosaurus.com/cachedir/spec.html}.
Various applications write cache directory tags into directories they
use to hold regenerable, non-precious data, so that such data can be
-more easily excluded from backups.
+more easily excluded from backups.
-@menu
-* controlling pattern-matching with exclude::
-* problems with exclude::
-@end menu
+There are three @samp{exclude-caches} options, each providing a different
+exclusion semantics:
-@node controlling pattern-matching with exclude
-@unnumberedsubsec Controlling Pattern-Matching with the @code{exclude} Options
+@table @option
+@opindex exclude-caches
+@item --exclude-caches
+Do not archive the contents of the directory, but archive the
+directory itself and the @file{CACHEDIR.TAG} file.
-Normally, a pattern matches a name if an initial subsequence of the
-name's components matches the pattern, where @samp{*}, @samp{?}, and
-@samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards,
-and wildcards can match @samp{/}.
+@opindex exclude-caches-under
+@item --exclude-caches-under
+Do not archive the contents of the directory, nor the
+@file{CACHEDIR.TAG} file, archive only the directory itself.
-Other than optionally stripping leading @samp{/} from names
-(@pxref{absolute}), patterns and names are used as-is. For
-example, trailing @samp{/} is not trimmed from a user-specified name
-before deciding whether to exclude it.
+@opindex exclude-caches-all
+@item --exclude-caches-all
+Omit directories containing @file{CACHEDIR.TAG} file entirely.
+@end table
-However, this matching procedure can be altered by the options listed
-below. These options accumulate. For example:
+@findex exclude-tag
+Another option family, @option{--exclude-tag}, provides a generalization of
+this concept. It takes a single argument, a file name to look for.
+Any directory that contains this file will be excluded from the dump.
+Similarly to @samp{exclude-caches}, there are three options in this
+option family:
+
+@table @option
+@opindex exclude-tag
+@item --exclude-tag=@var{file}
+Do not dump the contents of the directory, but dump the
+directory itself and the @var{file}.
+
+@opindex exclude-tag-under
+@item --exclude-tag-under=@var{file}
+Do not dump the contents of the directory, nor the
+@var{file}, archive only the directory itself.
+
+@opindex exclude-tag-all
+@item --exclude-tag-all=@var{file}
+Omit directories containing @var{file} file entirely.
+@end table
+
+Multiple @option{--exclude-tag*} options can be given.
+
+For example, given this directory:
@smallexample
---ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
+@group
+$ @kbd{find dir}
+dir
+dir/blues
+dir/jazz
+dir/folk
+dir/folk/tagfile
+dir/folk/sanjuan
+dir/folk/trote
+@end group
@end smallexample
-ignores case when excluding @samp{makefile}, but not when excluding
-@samp{readme}.
+The @option{--exclude-tag} will produce the following:
-@table @option
-@opindex anchored
-@opindex no-anchored
-@item --anchored
-@itemx --no-anchored
-If anchored, a pattern must match an initial subsequence
-of the name's components. Otherwise, the pattern can match any
-subsequence. Default is @option{--no-anchored}.
+@smallexample
+$ @kbd{tar -cf archive.tar --exclude-tag=tagfile -v dir}
+dir/
+dir/blues
+dir/jazz
+dir/folk/
+tar: dir/folk/: contains a cache directory tag tagfile;
+ contents not dumped
+dir/folk/tagfile
+@end smallexample
-@opindex ignore-case
-@opindex no-ignore-case
-@item --ignore-case
-@itemx --no-ignore-case
-When ignoring case, upper-case patterns match lower-case names and vice versa.
-When not ignoring case (the default), matching is case-sensitive.
+Both the @file{dir/folk} directory and its tagfile are preserved in
+the archive, however the rest of files in this directory are not.
-@opindex wildcards
-@opindex no-wildcards
-@item --wildcards
-@itemx --no-wildcards
-When using wildcards (the default), @samp{*}, @samp{?}, and @samp{[...]}
-are the usual shell wildcards, and @samp{\} escapes wildcards.
-Otherwise, none of these characters are special, and patterns must match
-names literally.
+Now, using the @option{--exclude-tag-under} option will exclude
+@file{tagfile} from the dump, while still preserving the directory
+itself, as shown in this example:
-@opindex wildcards-match-slash
-@opindex no-wildcards-match-slash
-@item --wildcards-match-slash
-@itemx --no-wildcards-match-slash
-When wildcards match slash (the default), a wildcard like @samp{*} in
-the pattern can match a @samp{/} in the name. Otherwise, @samp{/} is
-matched only by @samp{/}.
+@smallexample
+$ @kbd{tar -cf archive.tar --exclude-tag-under=tagfile -v dir}
+dir/
+dir/blues
+dir/jazz
+dir/folk/
+./tar: dir/folk/: contains a cache directory tag tagfile;
+ contents not dumped
+@end smallexample
-@end table
+Finally, using @option{--exclude-tag-all} omits the @file{dir/folk}
+directory entirely:
-The @option{--recursion} and @option{--no-recursion} options
-(@pxref{recurse}) also affect how exclude patterns are interpreted. If
-recursion is in effect, a pattern excludes a name if it matches any of
-the name's parent directories.
+@smallexample
+$ @kbd{tar -cf archive.tar --exclude-tag-all=tagfile -v dir}
+dir/
+dir/blues
+dir/jazz
+./tar: dir/folk/: contains a cache directory tag tagfile;
+ directory not dumped
+@end smallexample
+
+@menu
+* problems with exclude::
+@end menu
@node problems with exclude
@unnumberedsubsec Problems with Using the @code{exclude} Options
-@opindex exclude, potential problems with
+@xopindex{exclude, potential problems with}
Some users find @samp{exclude} options confusing. Here are some common
pitfalls:
@itemize @bullet
@item
-The main operating mode of @command{tar} does not act on a path name
-explicitly listed on the command line if one of its file name
+The main operating mode of @command{tar} does not act on a file name
+explicitly listed on the command line, if one of its file name
components is excluded. In the example above, if
you create an archive and exclude files that end with @samp{*.o}, but
explicitly name the file @samp{dir.o/foo} after all the options have been
to be excluded are given as a pattern on the command line. Use
@option{--exclude-from} 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.
+zero, one, or many files.
@item
-When you use @option{--exclude=@var{pattern}}, be sure to quote the @var{pattern}
-parameter, so @GNUTAR{} sees wildcard characters
+When you use @option{--exclude=@var{pattern}}, be sure to quote the
+@var{pattern} parameter, so @GNUTAR{} sees wildcard characters
like @samp{*}. If you do not do this, the shell might expand the
@samp{*} itself using files at hand, so @command{tar} might receive a
list of files instead of one pattern, or none at all, making the
rather than:
@smallexample
+# @emph{Wrong!}
$ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}}
@end smallexample
might fail.
@item
+@FIXME{The change in semantics must have occurred before 1.11,
+so I doubt if it is worth mentioning at all. Anyway, should at
+least specify in which version the semantics changed.}
In earlier versions of @command{tar}, what is now the
@option{--exclude-from} option was called @option{--exclude} instead.
Now, @option{--exclude} applies to patterns listed on the command
line and @option{--exclude-from} applies to patterns listed in a
-file.
+file.
@end itemize
-@node Wildcards
+@node wildcards
@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, @command{tar} often
-uses wildcard patterns for matching (or globbing) archive members instead
-of actual files in the file system. Wildcard patterns are also used for
+existing files matching the given pattern. @GNUTAR{} can use wildcard
+patterns for matching (or globbing) archive members when extracting
+from or listing an archive. Wildcard patterns are also used for
verifying volume labels of @command{tar} archives. This section has the
purpose of explaining wildcard syntax for @command{tar}.
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.
+string: thus, excluding a directory also excludes all the files beneath it.
-@node after
-@section Operating Only on New Files
-@UNREVISED
+@menu
+* controlling pattern-matching::
+@end menu
-@cindex Excluding file by age
-@cindex Data Modification time, excluding files by
-@cindex Modification time, excluding files by
-@cindex Age, excluding files by
-The @option{--after-date=@var{date}} (@option{--newer=@var{date}},
-@option{-N @var{date}}) option causes @command{tar} to only work on
-files whose data modification or status change times are newer than
-the @var{date} given. If @var{date} starts with @samp{/} or @samp{.},
-it is taken to be a file name; the data modification time of that file
-is used as the date. If you use this option when creating or appending
-to an archive, the archive will only include new files. If you use
-@option{--after-date} when extracting an archive, @command{tar} will
-only extract files newer than the @var{date} you specify.
+@node controlling pattern-matching
+@unnumberedsubsec Controlling Pattern-Matching
-If you only want @command{tar} to make the date comparison based on
-modification of the file's data (rather than status
-changes), then use the @option{--newer-mtime=@var{date}} option.
+For the purposes of this section, we call @dfn{exclusion members} all
+member names obtained while processing @option{--exclude} and
+@option{--exclude-from} options, and @dfn{inclusion members} those
+member names that were given in the command line or read from the file
+specified with @option{--files-from} option.
-You may use these options with any operation. Note that these options
-differ from the @option{--update} (@option{-u}) operation in that they
-allow you to specify a particular date against which @command{tar} can
-compare when deciding whether or not to archive the files.
+These two pairs of member lists are used in the following operations:
+@option{--diff}, @option{--extract}, @option{--list},
+@option{--update}.
-@table @option
-@opindex after-date
-@opindex newer
-@item --after-date=@var{date}
-@itemx --newer=@var{date}
-@itemx -N @var{date}
-Only store files newer than @var{date}.
+There are no inclusion members in create mode (@option{--create} and
+@option{--append}), since in this mode the names obtained from the
+command line refer to @emph{files}, not archive members.
-Acts on files only if their data modification or status change times are
-later than @var{date}. Use in conjunction with any operation.
+By default, inclusion members are compared with archive members
+literally @footnote{Notice that earlier @GNUTAR{} versions used
+globbing for inclusion members, which contradicted to UNIX98
+specification and was not documented. @xref{Changes}, for more
+information on this and other changes.} and exclusion members are
+treated as globbing patterns. For example:
-If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
-name; the data modification time of that file is used as the date.
+@smallexample
+@group
+$ @kbd{tar tf foo.tar}
+a.c
+b.c
+a.txt
+[remarks]
+# @i{Member names are used verbatim:}
+$ @kbd{tar -xf foo.tar -v '[remarks]'}
+[remarks]
+# @i{Exclude member names are globbed:}
+$ @kbd{tar -xf foo.tar -v --exclude '*.c'}
+a.txt
+[remarks]
+@end group
+@end smallexample
-@opindex newer-mtime
-@item --newer-mtime=@var{date}
-Acts like @option{--after-date}, but only looks at data modification times.
-@end table
+This behavior can be altered by using the following options:
-These options limit @command{tar} to operate only on files which have
-been modified after the date specified. A file's status is considered to have
-changed if its contents have been modified, or if its 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.)
+@table @option
+@opindex wildcards
+@item --wildcards
+Treat all member names as wildcards.
-Gurus would say that @option{--after-date} tests both the data
-modification time (@code{mtime}, the time the contents of the file
-were last modified) and the status change time (@code{ctime}, the time
-the file's status was last changed: owner, permissions, etc.@:)
-fields, while @option{--newer-mtime} tests only the @code{mtime}
-field.
+@opindex no-wildcards
+@item --no-wildcards
+Treat all member names as literal strings.
+@end table
-To be precise, @option{--after-date} checks @emph{both} @code{mtime} and
-@code{ctime} and processes the file if either one is more recent than
-@var{date}, while @option{--newer-mtime} only checks @code{mtime} and
-disregards @code{ctime}. Neither does it use @code{atime} (the last time the
-contents of the file were looked at).
+Thus, to extract files whose names end in @samp{.c}, you can use:
-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.
+@smallexample
+$ @kbd{tar -xf foo.tar -v --wildcards '*.c'}
+a.c
+b.c
+@end smallexample
-@FIXME{Need example of --newer-mtime with quoted argument.}
+@noindent
+Notice quoting of the pattern to prevent the shell from interpreting
+it.
-@quotation
-@strong{Please Note:} @option{--after-date} and @option{--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 Dumps}.
-@end quotation
+The effect of @option{--wildcards} option is canceled by
+@option{--no-wildcards}. This can be used to pass part of
+the command line arguments verbatim and other part as globbing
+patterns. For example, the following invocation:
+
+@smallexample
+$ @kbd{tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'}
+@end smallexample
@noindent
-@FIXME{which tells -- need to fill this in!}
+instructs @command{tar} to extract from @file{foo.tar} all files whose
+names end in @samp{.txt} and the file named @file{[remarks]}.
-@node recurse
-@section Descending into Directories
-@UNREVISED
-@cindex Avoiding recursion in directories
-@cindex Descending directories, avoiding
-@cindex Directories, avoiding recursion
-@cindex Recursion in directories, avoiding
+Normally, a pattern matches a name if an initial subsequence of the
+name's components matches the pattern, where @samp{*}, @samp{?}, and
+@samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards,
+and wildcards can match @samp{/}.
-@FIXME{arrggh! this is still somewhat confusing to me. :-< }
+Other than optionally stripping leading @samp{/} from names
+(@pxref{absolute}), patterns and names are used as-is. For
+example, trailing @samp{/} is not trimmed from a user-specified name
+before deciding whether to exclude it.
-@FIXME{show dan bob's comments, from 2-10-97}
+However, this matching procedure can be altered by the options listed
+below. These options accumulate. For example:
-Usually, @command{tar} will recursively explore all directories (either
-those given on the command line or through the @option{--files-from}
-option) for the various files they contain. However, you may not always
-want @command{tar} to act this way.
+@smallexample
+--ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
+@end smallexample
-@opindex no-recursion
-The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
-into specified directories. If you specify @option{--no-recursion}, you can
-use the @command{find} utility for hunting through levels of directories to
-construct a list of file names which you could then pass to @command{tar}.
-@command{find} allows you to be more selective when choosing which files to
-archive; see @ref{files} for more information on using @command{find} with
-@command{tar}, or look.
+@noindent
+ignores case when excluding @samp{makefile}, but not when excluding
+@samp{readme}.
@table @option
-@item --no-recursion
-Prevents @command{tar} from recursively descending directories.
-
-@opindex recursion
-@item --recursion
-Requires @command{tar} to recursively descend directories.
-This is the default.
-@end table
+@opindex anchored
+@opindex no-anchored
+@item --anchored
+@itemx --no-anchored
+If anchored, a pattern must match an initial subsequence
+of the name's components. Otherwise, the pattern can match any
+subsequence. Default is @option{--no-anchored} for exclusion members
+and @option{--anchored} inclusion members.
-When you use @option{--no-recursion}, @GNUTAR{} grabs
-directory entries themselves, but does not descend on them
-recursively. Many people use @command{find} for locating files they
-want to back up, and since @command{tar} @emph{usually} recursively
-descends on directories, they have to use the @samp{@w{! -d}} option
-to @command{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 @option{--files-from} option to archive the files
-located via @command{find}.
-
-The problem when restoring files archived in this manner is that the
-directories themselves are not in the archive; so the
-@option{--same-permissions} (@option{--preserve-permissions},
-@option{-p}) option does not affect them---while users might really
-like it to. Specifying @option{--no-recursion} is a way to tell
-@command{tar} to grab only the directory entries given to it, adding
-no new files on its own.
-
-The @option{--no-recursion} option also applies when extracting: it
-causes @command{tar} to extract only the matched directory entries, not
-the files under those directories.
-
-The @option{--no-recursion} option also affects how exclude patterns
-are interpreted (@pxref{controlling pattern-matching with exclude}).
+@opindex ignore-case
+@opindex no-ignore-case
+@item --ignore-case
+@itemx --no-ignore-case
+When ignoring case, upper-case patterns match lower-case names and vice versa.
+When not ignoring case (the default), matching is case-sensitive.
-The @option{--no-recursion} and @option{--recursion} options apply to
-later options and operands, and can be overridden by later occurrences
-of @option{--no-recursion} and @option{--recursion}. For example:
+@opindex wildcards-match-slash
+@opindex no-wildcards-match-slash
+@item --wildcards-match-slash
+@itemx --no-wildcards-match-slash
+When wildcards match slash (the default for exclusion members), a
+wildcard like @samp{*} in the pattern can match a @samp{/} in the
+name. Otherwise, @samp{/} is matched only by @samp{/}.
-@smallexample
-$ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord}
-@end smallexample
+@end table
-@noindent
-creates an archive with one entry for @file{grape}, and the recursive
-contents of @file{grape/concord}, but no entries under @file{grape}
-other than @file{grape/concord}.
+The @option{--recursion} and @option{--no-recursion} options
+(@pxref{recurse}) also affect how member patterns are interpreted. If
+recursion is in effect, a pattern matches a name if it matches any of
+the name's parent directories.
-@node one
-@section Crossing File System Boundaries
-@cindex File system boundaries, not crossing
-@UNREVISED
+The following table summarizes pattern-matching default values:
-@command{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 @command{tar} and specifying
-@option{--one-file-system} (@option{-l}). This option only affects files that are
-archived because they are in a directory that is being archived;
-@command{tar} will still archive files explicitly named on the command line
-or through @option{--files-from}, regardless of where they reside.
+@multitable @columnfractions .3 .7
+@headitem Members @tab Default settings
+@item Inclusion @tab @option{--no-wildcards --anchored --no-wildcards-match-slash}
+@item Exclusion @tab @option{--wildcards --no-anchored --wildcards-match-slash}
+@end multitable
-@table @option
-@opindex one-file-system
-@item --one-file-system
-@itemx -l
-Prevents @command{tar} from crossing file system boundaries when
-archiving. Use in conjunction with any write operation.
-@end table
+@node quoting styles
+@section Quoting Member Names
-The @option{--one-file-system} option causes @command{tar} to modify its
-normal behavior in archiving the contents of directories. If a file in
-a directory is not on the same file system as the directory itself, then
-@command{tar} will not archive that file. If the file is a directory
-itself, @command{tar} will not archive anything beneath it; in other words,
-@command{tar} will not cross mount points.
+When displaying member names, @command{tar} takes care to avoid
+ambiguities caused by certain characters. This is called @dfn{name
+quoting}. The characters in question are:
-It is reported that using this option, the mount point is is archived,
-but nothing under it.
+@itemize @bullet
+@item Non-printable control characters:
+@anchor{escape sequences}
+@multitable @columnfractions 0.20 0.10 0.60
+@headitem Character @tab @acronym{ASCII} @tab Character name
+@item \a @tab 7 @tab Audible bell
+@item \b @tab 8 @tab Backspace
+@item \f @tab 12 @tab Form feed
+@item \n @tab 10 @tab New line
+@item \r @tab 13 @tab Carriage return
+@item \t @tab 9 @tab Horizontal tabulation
+@item \v @tab 11 @tab Vertical tabulation
+@end multitable
-This option is useful for making full or incremental archival backups of
-a file system. If this option is used in conjunction with
-@option{--verbose} (@option{-v}), files that are excluded are mentioned by name on the
-standard error.
+@item Space (@acronym{ASCII} 32)
-@menu
-* directory:: Changing Directory
-* absolute:: Absolute File Names
-@end menu
+@item Single and double quotes (@samp{'} and @samp{"})
-@node directory
-@subsection Changing the Working Directory
-@UNREVISED
+@item Backslash (@samp{\})
+@end itemize
-@FIXME{need to read over this node now for continuity; i've switched
-things around some.}
+The exact way @command{tar} uses to quote these characters depends on
+the @dfn{quoting style}. The default quoting style, called
+@dfn{escape} (see below), uses backslash notation to represent control
+characters, space and backslash. Using this quoting style, control
+characters are represented as listed in column @samp{Character} in the
+above table, a space is printed as @samp{\ } and a backslash as @samp{\\}.
-@cindex Changing directory mid-stream
-@cindex Directory, changing mid-stream
-@cindex Working directory, specifying
-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
-@option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}).
-This will change the working directory to the specified directory
-after that point in the list.
+@GNUTAR{} offers seven distinct quoting styles, which can be selected
+using @option{--quoting-style} option:
@table @option
-@opindex directory
-@item --directory=@var{directory}
-@itemx -C @var{directory}
-Changes the working directory in the middle of a command line.
+@item --quoting-style=@var{style}
+@opindex quoting-style
+
+Sets quoting style. Valid values for @var{style} argument are:
+literal, shell, shell-always, c, escape, locale, clocale.
@end table
-For example,
+These styles are described in detail below. To illustrate their
+effect, we will use an imaginary tar archive @file{arch.tar}
+containing the following members:
@smallexample
-$ @kbd{tar -c -f jams.tar grape prune -C food cherry}
+@group
+# 1. Contains horizontal tabulation character.
+a tab
+# 2. Contains newline character
+a
+newline
+# 3. Contains a space
+a space
+# 4. Contains double quotes
+a"double"quote
+# 5. Contains single quotes
+a'single'quote
+# 6. Contains a backslash character:
+a\backslash
+@end group
@end smallexample
-@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.
+Here is how usual @command{ls} command would have listed them, if they
+had existed in the current working directory:
-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.
+@smallexample
+@group
+$ @kbd{ls}
+a\ttab
+a\nnewline
+a\ space
+a"double"quote
+a'single'quote
+a\\backslash
+@end group
+@end smallexample
-Contrast this with the command,
+Quoting styles:
+
+@table @samp
+@item literal
+No quoting, display each character as is:
@smallexample
-$ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
+@group
+$ @kbd{tar tf arch.tar --quoting-style=literal}
+./
+./a space
+./a'single'quote
+./a"double"quote
+./a\backslash
+./a tab
+./a
+newline
+@end group
@end smallexample
-@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 @option{--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}:
+@item shell
+Display characters the same way Bourne shell does:
+control characters, except @samp{\t} and @samp{\n}, are printed using
+backslash escapes, @samp{\t} and @samp{\n} are printed as is, and a
+single quote is printed as @samp{\'}. If a name contains any quoted
+characters, it is enclosed in single quotes. In particular, if a name
+contains single quotes, it is printed as several single-quoted strings:
@smallexample
-$ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
+@group
+$ @kbd{tar tf arch.tar --quoting-style=shell}
+./
+'./a space'
+'./a'\''single'\''quote'
+'./a"double"quote'
+'./a\backslash'
+'./a tab'
+'./a
+newline'
+@end group
@end smallexample
-@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.
+@item shell-always
+Same as @samp{shell}, but the names are always enclosed in single
+quotes:
-Note that @option{--directory} options are interpreted consecutively. If
-@option{--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 @command{tar}, due to a previous
-@option{--directory} option.
+@smallexample
+@group
+$ @kbd{tar tf arch.tar --quoting-style=shell-always}
+'./'
+'./a space'
+'./a'\''single'\''quote'
+'./a"double"quote'
+'./a\backslash'
+'./a tab'
+'./a
+newline'
+@end group
+@end smallexample
-When using @option{--files-from} (@pxref{files}), you can put various
-@command{tar} options (including @option{-C}) in the file list. Notice,
-however, that in this case the option and its argument may not be
-separated by whitespace. If you use short option, its argument must
-either follow the option letter immediately, without any intervening
-whitespace, or occupy the next line. Otherwise, if you use long
-option, separate its argument by an equal sign.
+@item c
+Use the notation of the C programming language. All names are
+enclosed in double quotes. Control characters are quoted using
+backslash notations, double quotes are represented as @samp{\"},
+backslash characters are represented as @samp{\\}. Single quotes and
+spaces are not quoted:
-For instance, the file list for the above example will be:
+@smallexample
+@group
+$ @kbd{tar tf arch.tar --quoting-style=c}
+"./"
+"./a space"
+"./a'single'quote"
+"./a\"double\"quote"
+"./a\\backslash"
+"./a\ttab"
+"./a\nnewline"
+@end group
+@end smallexample
+
+@item escape
+Control characters are printed using backslash notation, a space is
+printed as @samp{\ } and a backslash as @samp{\\}. This is the
+default quoting style, unless it was changed when configured the
+package.
@smallexample
@group
--C
-/etc
-passwd
-hosts
--C
-/lib
-libc.a
+$ @kbd{tar tf arch.tar --quoting-style=escape}
+./
+./a space
+./a'single'quote
+./a"double"quote
+./a\\backslash
+./a\ttab
+./a\nnewline
@end group
@end smallexample
-@noindent
-To use it, you would invoke @command{tar} as follows:
+@item locale
+Control characters, single quote and backslash are printed using
+backslash notation. All names are quoted using left and right
+quotation marks, appropriate to the current locale. If it does not
+define quotation marks, use @samp{`} as left and @samp{'} as right
+quotation marks. Any occurrences of the right quotation mark in a
+name are escaped with @samp{\}, for example:
+
+For example:
@smallexample
-$ @kbd{tar -c -f foo.tar --files-from list}
+@group
+$ @kbd{tar tf arch.tar --quoting-style=locale}
+`./'
+`./a space'
+`./a\'single\'quote'
+`./a"double"quote'
+`./a\\backslash'
+`./a\ttab'
+`./a\nnewline'
+@end group
@end smallexample
-Notice also that you can only use the short option variant in the file
-list, i.e., always use @option{-C}, not @option{--directory}.
+@item clocale
+Same as @samp{locale}, but @samp{"} is used for both left and right
+quotation marks, if not provided by the currently selected locale:
-The interpretation of @option{--directory} is disabled by
-@option{--null} option.
+@smallexample
+@group
+$ @kbd{tar tf arch.tar --quoting-style=clocale}
+"./"
+"./a space"
+"./a'single'quote"
+"./a\"double\"quote"
+"./a\\backslash"
+"./a\ttab"
+"./a\nnewline"
+@end group
+@end smallexample
+@end table
-@node absolute
-@subsection Absolute File Names
-@UNREVISED
+You can specify which characters should be quoted in addition to those
+implied by the current quoting style:
@table @option
-@opindex absolute-names
-@item --absolute-names
-@itemx -P
-Do not strip leading slashes from file names, and permit file names
-containing a @file{..} file name component.
+@item --quote-chars=@var{string}
+Always quote characters from @var{string}, even if the selected
+quoting style would not quote them.
@end table
-By default, @GNUTAR{} drops a leading @samp{/} on
-input or output, and complains about file names containing a @file{..}
-component. This option turns off this behavior.
+For example, using @samp{escape} quoting (compare with the usual
+escape listing above):
-When @command{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}, @command{tar} will extract it as if the name were
-really @file{etc/passwd}.
+@smallexample
+@group
+$ @kbd{tar tf arch.tar --quoting-style=escape --quote-chars=' "'}
+./
+./a\ space
+./a'single'quote
+./a\"double\"quote
+./a\\backslash
+./a\ttab
+./a\nnewline
+@end group
+@end smallexample
-File names containing @file{..} can cause problems when extracting, so
-@command{tar} normally warns you about such files when creating an
-archive, and rejects attempts to extracts such files.
+To disable quoting of such additional characters, use the following
+option:
-Other @command{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-@GNUTAR{}
-program to use. Therefore, @GNUTAR{} also strips
-leading slashes from member names when putting members into the
-archive. For example, if you ask @command{tar} to add the file
-@file{/bin/ls} to an archive, it will do so, but the member name will
-be @file{bin/ls}.@footnote{A side effect of this is that when
-@option{--create} is used with @option{--verbose} the resulting output
-is not, generally speaking, the same as the one you'd get running
-@kbd{tar --list} command. This may be important if you use some
-scripts for comparing both outputs. @xref{listing member and file names},
-for the information on how to handle this case.}
+@table @option
+@item --no-quote-chars=@var{string}
+Remove characters listed in @var{string} from the list of quoted
+characters set by the previous @option{--quote-chars} option.
+@end table
-If you use the @option{--absolute-names} (@option{-P}) option,
-@command{tar} will do none of these transformations.
+This option is particularly useful if you have added
+@option{--quote-chars} to your @env{TAR_OPTIONS} (@pxref{TAR_OPTIONS})
+and wish to disable it for the current invocation.
+
+Note, that @option{--no-quote-chars} does @emph{not} disable those
+characters that are quoted by default in the selected quoting style.
+
+@node transform
+@section Modifying File and Member Names
+
+@command{Tar} archives contain detailed information about files stored
+in them and full file names are part of that information. When
+storing file to an archive, its file name is recorded in it,
+along with the actual file contents. When restoring from an archive,
+a file is created on disk with exactly the same name as that stored
+in the archive. In the majority of cases this is the desired behavior
+of a file archiver. However, there are some cases when it is not.
+
+First of all, it is often unsafe to extract archive members with
+absolute file names or those that begin with a @file{../}. @GNUTAR{}
+takes special precautions when extracting such names and provides a
+special option for handling them, which is described in
+@ref{absolute}.
+
+Secondly, you may wish to extract file names without some leading
+directory components, or with otherwise modified names. In other
+cases it is desirable to store files under differing names in the
+archive.
-To archive or extract files relative to the root directory, specify
-the @option{--absolute-names} (@option{-P}) option.
+@GNUTAR{} provides several options for these needs.
-Normally, @command{tar} acts on files relative to the working
-directory---ignoring superior directory names when archiving, and
-ignoring leading slashes when extracting.
+@table @option
+@opindex strip-components
+@item --strip-components=@var{number}
+Strip given @var{number} of leading components from file names before
+extraction.
+@end table
-When you specify @option{--absolute-names} (@option{-P}),
-@command{tar} stores file names including all superior directory
-names, and preserves leading slashes. If you only invoked
-@command{tar} from the root directory you would never need the
-@option{--absolute-names} option, but using this option
-may be more convenient than switching to root.
+For example, suppose you have archived whole @file{/usr} hierarchy to
+a tar archive named @file{usr.tar}. Among other files, this archive
+contains @file{usr/include/stdlib.h}, which you wish to extract to
+the current working directory. To do so, you type:
-@FIXME{Should be an example in the tutorial/wizardry section using this
-to transfer files between systems.}
+@smallexample
+$ @kbd{tar -xf usr.tar --strip=2 usr/include/stdlib.h}
+@end smallexample
-@FIXME{Is write access an issue?}
+The option @option{--strip=2} instructs @command{tar} to strip the
+two leading components (@file{usr/} and @file{include/}) off the file
+name.
-@table @option
-@item --absolute-names
-Preserves full file names (including superior directory names) when
-archiving files. Preserves leading slash when extracting files.
+If you add the @option{--verbose} (@option{-v}) option to the invocation
+above, you will note that the verbose listing still contains the
+full file name, with the two removed components still in place. This
+can be inconvenient, so @command{tar} provides a special option for
+altering this behavior:
+@anchor{show-transformed-names}
+@table @option
+@opindex show-transformed-names
+@item --show-transformed-names
+Display file or member names with all requested transformations
+applied.
@end table
-@FIXME{this is still horrible; need to talk with dan on monday.}
-
-@command{tar} prints out a message about removing the @samp{/} from
-file names. This message appears once per @GNUTAR{}
-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 @command{tar} standard
-error to the sink. For example, under @command{sh}:
+@noindent
+For example:
@smallexample
-$ @kbd{tar -c -f archive.tar /home 2> /dev/null}
+@group
+$ @kbd{tar -xf usr.tar -v --strip=2 usr/include/stdlib.h}
+usr/include/stdlib.h
+$ @kbd{tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h}
+stdlib.h
+@end group
+@end smallexample
+
+Notice that in both cases the file @file{stdlib.h} is extracted to the
+current working directory, @option{--show-transformed-names} affects
+only the way its name is displayed.
+
+This option is especially useful for verifying whether the invocation
+will have the desired effect. Thus, before running
+
+@smallexample
+$ @kbd{tar -x --strip=@var{n}}
@end smallexample
@noindent
-Another solution, both nicer and simpler, would be to change to
-the @file{/} directory first, and then avoid absolute notation.
-For example:
+it is often advisable to run
@smallexample
-$ @kbd{(cd / && tar -c -f archive.tar home)}
-$ @kbd{tar -c -f archive.tar -C / home}
+$ @kbd{tar -t -v --show-transformed --strip=@var{n}}
@end smallexample
-@include getdate.texi
+@noindent
+to make sure the command will produce the intended results.
-@node Formats
-@chapter Controlling the Archive Format
+In case you need to apply more complex modifications to the file name,
+@GNUTAR{} provides a general-purpose transformation option:
-@cindex Tar archive formats
-Due to historical reasons, there are several formats of tar archives.
-All of them are based on the same principles, but have some subtle
-differences that often make them incompatible with each other.
+@table @option
+@opindex transform
+@opindex xform
+@item --transform=@var{expression}
+@itemx --xform=@var{expression}
+Modify file names using supplied @var{expression}.
+@end table
-GNU tar is able to create and handle archives in a variety of formats.
-The most frequently used formats are (in alphabetical order):
+@noindent
+The @var{expression} is a @command{sed}-like replace expression of the
+form:
-@table @asis
-@item gnu
-Format used by @GNUTAR{} versions up to 1.13.25. This format derived
-from an early @acronym{POSIX} standard, adding some improvements such as
-sparse file handling and incremental archives. Unfortunately these
-features were implemented in a way incompatible with other archive
-formats.
+@smallexample
+s/@var{regexp}/@var{replace}/[@var{flags}]
+@end smallexample
-Archives in @samp{gnu} format are able to hold pathnames of unlimited
-length.
+@noindent
+where @var{regexp} is a @dfn{regular expression}, @var{replace} is a
+replacement for each file name part that matches @var{regexp}. Both
+@var{regexp} and @var{replace} are described in detail in
+@ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}.
-@item oldgnu
-Format used by @GNUTAR{} of versions prior to 1.12.
+Any delimiter can be used in lieue of @samp{/}, the only requirement being
+that it be used consistently throughout the expression. For example,
+the following two expressions are equivalent:
-@item v7
-Archive format, compatible with the V7 implementation of tar. This
-format imposes a number of limitations. The most important of them
-are:
+@smallexample
+@group
+s/one/two/
+s,one,two,
+@end group
+@end smallexample
-@enumerate
-@item The maximum length of a file name is limited to 99 characters.
-@item The maximum length of a symbolic link is limited to 99 characters.
-@item It is impossible to store special files (block and character
-devices, fifos etc.)
-@item Maximum value of user or group ID is limited to 2097151 (7777777
-octal)
-@item V7 archives do not contain symbolic ownership information (user
-and group name of the file owner).
-@end enumerate
+Changing delimiters is often useful when the @var{regex} contains
+slashes. For example, it is more convenient to write @code{s,/,-,} than
+@code{s/\//-/}.
-This format has traditionally been used by Automake when producing
-Makefiles. This practice will change in the future, in the meantime,
-however this means that projects containing filenames more than 99
-characters long will not be able to use @GNUTAR{} @value{VERSION} and
-Automake prior to 1.9.
+As in @command{sed}, you can give several replace expressions,
+separated by a semicolon.
-@item ustar
-Archive format defined by @acronym{POSIX.1-1988} specification. It stores
-symbolic ownership information. It is also able to store
-special files. However, it imposes several restrictions as well:
+Supported @var{flags} are:
-@enumerate
-@item The maximum length of a file name is limited to 256 characters,
-provided that the filename can be split at directory separator in
-two parts, first of them being at most 155 bytes long. So, in most
-cases the maximum file name length will be shorter than 256
-characters.
-@item The maximum length of a symbolic link name is limited to
-100 characters.
-@item Maximum size of a file the archive is able to accomodate
-is 8GB
-@item Maximum value of UID/GID is 2097151.
-@item Maximum number of bits in device major and minor numbers is 21.
-@end enumerate
+@table @samp
+@item g
+Apply the replacement to @emph{all} matches to the @var{regexp}, not
+just the first.
-@item star
-Format used by J@"org Schilling @command{star}
-implementation. @GNUTAR{} is able to read @samp{star} archives but
-currently does not produce them.
+@item i
+Use case-insensitive matching
-@item posix
-Archive format defined by @acronym{POSIX.1-2001} specification. This is the
-most flexible and feature-rich format. It does not impose any
-restrictions on file sizes or filename lengths. This format is quite
-recent, so not all tar implementations are able to handle it properly.
-However, this format is designed in such a way that any tar
-implementation able to read @samp{ustar} archives will be able to read
-most @samp{posix} archives as well, with the only exception that any
-additional information (such as long file names etc.) will in such
-case be extracted as plain text files along with the files it refers to.
+@item x
+@var{regexp} is an @dfn{extended regular expression} (@pxref{Extended
+regexps, Extended regular expressions, Extended regular expressions,
+sed, GNU sed}).
-This archive format will be the default format for future versions
-of @GNUTAR{}.
+@item @var{number}
+Only replace the @var{number}th match of the @var{regexp}.
+
+Note: the @acronym{POSIX} standard does not specify what should happen
+when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{}
+follows the GNU @command{sed} implementation in this regard, so
+the interaction is defined to be: ignore matches before the
+@var{number}th, and then match and replace all matches from the
+@var{number}th on.
@end table
-The following table summarizes the limitations of each of these
-formats:
+In addition, several @dfn{transformation scope} flags are supported,
+that control to what files transformations apply. These are:
-@multitable @columnfractions .10 .20 .20 .20 .20
-@headitem Format @tab UID @tab File Size @tab Path Name @tab Devn
-@item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
-@item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
-@item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
-@item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
-@item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
-@end multitable
+@table @samp
+@item r
+Apply transformation to regular archive members.
-The default format for @GNUTAR{} is defined at compilation
-time. You may check it by running @command{tar --help}, and examining
-the last lines of its output. Usually, @GNUTAR{} is configured
-to create archives in @samp{gnu} format, however, future version will
-switch to @samp{posix}.
+@item R
+Do not apply transformation to regular archive members.
-@menu
-* Portability:: Making @command{tar} Archives More Portable
-* Compression:: Using Less Space through Compression
-* Attributes:: Handling File Attributes
-* Standard:: The Standard Format
-* Extensions:: @acronym{GNU} Extensions to the Archive Format
-* cpio:: Comparison of @command{tar} and @command{cpio}
-@end menu
+@item s
+Apply transformation to symbolic link targets.
-@node Portability
-@section Making @command{tar} Archives More Portable
+@item S
+Do not apply transformation to symbolic link targets.
-Creating a @command{tar} archive on a particular system that is meant to be
-useful later on many other machines and with other versions of @command{tar}
-is more challenging than you might think. @command{tar} archive formats
-have been evolving since the first versions of Unix. Many such formats
-are around, and are not always compatible with each other. This section
-discusses a few problems, and gives some advice about making @command{tar}
-archives more portable.
+@item h
+Apply transformation to hard link targets.
-One golden rule is simplicity. For example, limit your @command{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.
+@item H
+Do not apply transformation to hard link targets.
+@end table
-@FIXME{Discuss GNU extensions (incremental backups, multi-volume
-archives and archive labels) in GNU and PAX formats.}
+Default is @samp{rsh}, which means to apply tranformations to both archive
+members and targets of symbolic and hard links.
-@menu
-* Portable Names:: Portable Names
-* dereference:: Symbolic Links
-* old:: Old V7 Archives
-* ustar:: Ustar Archives
-* gnu:: GNU and old GNU format archives.
-* posix:: @acronym{POSIX} archives
-* Checksumming:: Checksumming Problems
-* Large or Negative Values:: Large files, negative time stamps, etc.
-@end menu
+Default scope flags can also be changed using @samp{flags=} statement
+in the transform expression. The flags set this way remain in force
+until next @samp{flags=} statement or end of expression, whichever
+occurs first. For example:
-@node Portable Names
-@subsection Portable Names
+@smallexample
+ --transform 'flags=S;s|^|/usr/local/|'
+@end smallexample
-Use portable file and member names. A name is portable if it contains
-only ASCII letters and digits, @samp{/}, @samp{.}, @samp{_}, and
-@samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or
-contain @samp{/-}. Avoid deep directory nesting. For portability to
-old Unix hosts, limit your file name components to 14 characters or
-less.
+Here are several examples of @option{--transform} usage:
-If you intend to have your @command{tar} archives to be read under
-MSDOS, you should not rely on case distinction for file names, and you
-might use the @acronym{GNU} @command{doschk} program for helping you
-further diagnosing illegal MSDOS names, which are even more limited
-than System V's.
+@enumerate
+@item Extract @file{usr/} hierarchy into @file{usr/local/}:
-@node dereference
-@subsection Symbolic Links
-@cindex File names, using symbolic links
-@cindex Symbolic link as file name
+@smallexample
+$ @kbd{tar --transform='s,usr/,usr/local/,' -x -f arch.tar}
+@end smallexample
-@opindex dereference
-Normally, when @command{tar} archives a symbolic link, it writes a
-block to the archive naming the target of the link. In that way, the
-@command{tar} archive is a faithful record of the file system contents.
-@option{--dereference} (@option{-h}) is used with @option{--create} (@option{-c}), and causes
-@command{tar} to archive the files symbolic links point to, instead of
-the links themselves. When this option is used, when @command{tar}
-encounters a symbolic link, it will archive the linked-to file,
-instead of simply recording the presence of a symbolic link.
+@item Strip two leading directory components (equivalent to
+@option{--strip-components=2}):
-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 @command{tar}, an extracted file
-might be linked to a file name that no longer exists in the file
-system.
+@smallexample
+$ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar}
+@end smallexample
-If a linked-to file is encountered again by @command{tar} while creating
-the same archive, an entire second copy of it will be stored. (This
-@emph{might} be considered a bug.)
+@item Convert each file name to lower case:
-So, for portable archives, do not archive symbolic links as such,
-and use @option{--dereference} (@option{-h}): many systems do not support
-symbolic links, and moreover, your distribution might be unusable if
-it contains unresolved symbolic links.
+@smallexample
+$ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
+@end smallexample
-@node old
-@subsection Old V7 Archives
-@cindex Format, old style
-@cindex Old style format
-@cindex Old style archives
-@cindex v7 archive format
+@item Prepend @file{/prefix/} to each file name:
-Certain old versions of @command{tar} cannot handle additional
-information recorded by newer @command{tar} programs. To create an
-archive in V7 format (not ANSI), which can be read by these old
-versions, specify the @option{--format=v7} option in
-conjunction with the @option{--create} (@option{-c}) (@command{tar} also
-accepts @option{--portability} or @samp{op-old-archive} for this
-option). When you specify it,
-@command{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.
+@smallexample
+$ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar}
+@end smallexample
-When updating an archive, do not use @option{--format=v7}
-unless the archive was created using this option.
+@item Archive the @file{/lib} directory, prepending @samp{/usr/local}
+to each archive member:
-In most cases, a @emph{new} format archive can be read by an @emph{old}
-@command{tar} program without serious trouble, so this option should
-seldom be needed. On the other hand, most modern @command{tar}s are
-able to read old format archives, so it might be safer for you to
-always use @option{--format=v7} for your distributions.
+@smallexample
+$ @kbd{tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib}
+@end smallexample
+@end enumerate
-@node ustar
-@subsection Ustar Archive Format
+Notice the use of flags in the last example. The @file{/lib}
+directory often contains many symbolic links to files within it.
+It may look, for example, like this:
-@cindex ustar archive format
-Archive format defined by @acronym{POSIX}.1-1988 specification is called
-@code{ustar}. Although it is more flexible than the V7 format, it
-still has many restrictions (@xref{Formats,ustar}, for the detailed
-description of @code{ustar} format). Along with V7 format,
-@code{ustar} format is a good choice for archives intended to be read
-with other implementations of @command{tar}.
+@smallexample
+$ @kbd{ls -l}
+drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/
+-rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so
+lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so
+...
+@end smallexample
-To create archive in @code{ustar} format, use @option{--format=ustar}
-option in conjunction with the @option{--create} (@option{-c}).
+Using the expression @samp{s,^,/usr/local/,} would mean adding
+@samp{/usr/local} to both regular archive members and to link
+targets. In this case, @file{/lib/libc.so.6} would become:
-@node gnu
-@subsection @acronym{GNU} and old @GNUTAR{} format
+@smallexample
+ /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so
+@end smallexample
-@cindex GNU archive format
-@cindex Old GNU archive format
-@GNUTAR{} was based on an early draft of the
-@acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
-@command{tar}, such as the support for file names longer than 100
-characters, use portions of the @command{tar} header record which were
-specified in that @acronym{POSIX} draft as unused. Subsequent changes in
-@acronym{POSIX} have allocated the same parts of the header record for
-other purposes. As a result, @GNUTAR{} format is
-incompatible with the current @acronym{POSIX} specification, and with
-@command{tar} programs that follow it.
+This is definitely not desired. To avoid this, the @samp{S} flag
+are used, which excludes symbolic link targets from filename
+transformations. The result is:
-In the majority of cases, @command{tar} will be configured to create
-this format by default. This will change in the future releases, since
-we plan to make @samp{posix} format the default.
+@smallexample
+$ @kbd{tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \
+ --show-transformed /lib}
+drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/
+-rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so
+lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 ->
+libc-2.3.2.so
+@end smallexample
-To force creation a @GNUTAR{} archive, use option
-@option{--format=gnu}.
+Unlike @option{--strip-components}, @option{--transform} can be used
+in any @GNUTAR{} operation mode. For example, the following command
+adds files to the archive while replacing the leading @file{usr/}
+component with @file{var/}:
-@node posix
-@subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
+@smallexample
+$ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' /}
+@end smallexample
-@cindex POSIX archive format
-@cindex PAX archive format
-The version @value{VERSION} of @GNUTAR{} is able
-to read and create archives conforming to @acronym{POSIX.1-2001} standard.
+To test @option{--transform} effect we suggest using
+@option{--show-transformed-names} option:
-A @acronym{POSIX} conformant archive will be created if @command{tar}
-was given @option{--format=posix} option.
+@smallexample
+$ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' \
+ --verbose --show-transformed-names /}
+@end smallexample
-@node Checksumming
-@subsection Checksumming Problems
+If both @option{--strip-components} and @option{--transform} are used
+together, then @option{--transform} is applied first, and the required
+number of components is then stripped from its result.
-SunOS and HP-UX @command{tar} fail to accept archives created using
-@GNUTAR{} and containing non-ASCII file names, that
-is, file names having characters with the eight bit set, because they
-use signed checksums, while @GNUTAR{} uses unsigned
-checksums while creating archives, as per @acronym{POSIX} standards. On
-reading, @GNUTAR{} 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.
+You can use as many @option{--transform} options in a single command
+line as you want. The specified expressions will then be applied in
+order of their appearance. For example, the following two invocations
+are equivalent:
+
+@smallexample
+$ @kbd{tar -cf arch.tar --transform='s,/usr/var,/var/' \
+ --transform='s,/usr/local,/usr/,'}
+$ @kbd{tar -cf arch.tar \
+ --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'}
+@end smallexample
+
+@node after
+@section Operating Only on New Files
+@UNREVISED
+
+@cindex Excluding file by age
+@cindex Data Modification time, excluding files by
+@cindex Modification time, excluding files by
+@cindex Age, excluding files by
+The @option{--after-date=@var{date}} (@option{--newer=@var{date}},
+@option{-N @var{date}}) option causes @command{tar} to only work on
+files whose data modification or status change times are newer than
+the @var{date} given. If @var{date} starts with @samp{/} or @samp{.},
+it is taken to be a file name; the data modification time of that file
+is used as the date. If you use this option when creating or appending
+to an archive, the archive will only include new files. If you use
+@option{--after-date} when extracting an archive, @command{tar} will
+only extract files newer than the @var{date} you specify.
+
+If you only want @command{tar} to make the date comparison based on
+modification of the file's data (rather than status
+changes), then use the @option{--newer-mtime=@var{date}} option.
+
+You may use these options with any operation. Note that these options
+differ from the @option{--update} (@option{-u}) operation in that they
+allow you to specify a particular date against which @command{tar} can
+compare when deciding whether or not to archive the files.
+
+@table @option
+@opindex after-date
+@opindex newer
+@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 data modification or status change times are
+later than @var{date}. Use in conjunction with any operation.
+
+If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
+name; the data modification time of that file is used as the date.
+
+@opindex newer-mtime
+@item --newer-mtime=@var{date}
+Acts like @option{--after-date}, but only looks at data modification times.
+@end table
+
+These options limit @command{tar} to operate only on files which have
+been modified after the date specified. A file's status is considered to have
+changed if its contents have been modified, or if its 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 @option{--after-date} tests both the data
+modification time (@code{mtime}, the time the contents of the file
+were last modified) and the status change time (@code{ctime}, the time
+the file's status was last changed: owner, permissions, etc.@:)
+fields, while @option{--newer-mtime} tests only the @code{mtime}
+field.
+
+To be precise, @option{--after-date} checks @emph{both} @code{mtime} and
+@code{ctime} and processes the file if either one is more recent than
+@var{date}, while @option{--newer-mtime} only checks @code{mtime} and
+disregards @code{ctime}. Neither does it use @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. For example, the following command will add to the archive
+all the files modified less than two days ago:
+
+@smallexample
+$ @kbd{tar -cf foo.tar --newer-mtime '2 days ago'}
+@end smallexample
+
+When any of these options is used with the option @option{--verbose}
+(@pxref{verbose tutorial}) @GNUTAR{} will try to convert the specified
+date back to its textual representation and compare that with the
+one given with the option. If the two dates differ, @command{tar} will
+print a warning saying what date it will use. This is to help user
+ensure he is using the right date. For example:
+
+@smallexample
+@group
+$ @kbd{tar -c -f archive.tar --after-date='10 days ago' .}
+tar: Option --after-date: Treating date `10 days ago' as 2006-06-11
+13:19:37.232434
+@end group
+@end smallexample
+
+@quotation
+@strong{Please Note:} @option{--after-date} and @option{--newer-mtime}
+should not be used for incremental backups. @xref{Incremental Dumps},
+for proper way of creating incremental backups.
+@end quotation
+
+@node recurse
+@section Descending into Directories
+@UNREVISED
+@cindex Avoiding recursion in directories
+@cindex Descending directories, avoiding
+@cindex Directories, avoiding recursion
+@cindex Recursion in directories, avoiding
+
+@FIXME{arrggh! this is still somewhat confusing to me. :-< }
+
+Usually, @command{tar} will recursively explore all directories (either
+those given on the command line or through the @option{--files-from}
+option) for the various files they contain. However, you may not always
+want @command{tar} to act this way.
+
+@opindex no-recursion
+The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
+into specified directories. If you specify @option{--no-recursion}, you can
+use the @command{find} utility for hunting through levels of directories to
+construct a list of file names which you could then pass to @command{tar}.
+@command{find} allows you to be more selective when choosing which files to
+archive; see @ref{files}, for more information on using @command{find} with
+@command{tar}, or look.
+
+@table @option
+@item --no-recursion
+Prevents @command{tar} from recursively descending directories.
+
+@opindex recursion
+@item --recursion
+Requires @command{tar} to recursively descend directories.
+This is the default.
+@end table
+
+When you use @option{--no-recursion}, @GNUTAR{} grabs
+directory entries themselves, but does not descend on them
+recursively. Many people use @command{find} for locating files they
+want to back up, and since @command{tar} @emph{usually} recursively
+descends on directories, they have to use the @samp{@w{-not -type d}}
+test in their @command{find} invocation (@pxref{Type, Type, Type test,
+find, Finding Files}), as they usually do not want all the files in a
+directory. They then use the @option{--files-from} option to archive
+the files located via @command{find}.
+
+The problem when restoring files archived in this manner is that the
+directories themselves are not in the archive; so the
+@option{--same-permissions} (@option{--preserve-permissions},
+@option{-p}) option does not affect them---while users might really
+like it to. Specifying @option{--no-recursion} is a way to tell
+@command{tar} to grab only the directory entries given to it, adding
+no new files on its own. To summarize, if you use @command{find} to
+create a list of files to be stored in an archive, use it as follows:
+
+@smallexample
+@group
+$ @kbd{find @var{dir} @var{tests} | \
+ tar -cf @var{archive} -T - --no-recursion}
+@end group
+@end smallexample
+
+The @option{--no-recursion} option also applies when extracting: it
+causes @command{tar} to extract only the matched directory entries, not
+the files under those directories.
+
+The @option{--no-recursion} option also affects how globbing patterns
+are interpreted (@pxref{controlling pattern-matching}).
+
+The @option{--no-recursion} and @option{--recursion} options apply to
+later options and operands, and can be overridden by later occurrences
+of @option{--no-recursion} and @option{--recursion}. For example:
+
+@smallexample
+$ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord}
+@end smallexample
+
+@noindent
+creates an archive with one entry for @file{grape}, and the recursive
+contents of @file{grape/concord}, but no entries under @file{grape}
+other than @file{grape/concord}.
+
+@node one
+@section Crossing File System Boundaries
+@cindex File system boundaries, not crossing
+@UNREVISED
+
+@command{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 @command{tar} and specifying
+@option{--one-file-system}. This option only affects files that are
+archived because they are in a directory that is being archived;
+@command{tar} will still archive files explicitly named on the command line
+or through @option{--files-from}, regardless of where they reside.
+
+@table @option
+@opindex one-file-system
+@item --one-file-system
+Prevents @command{tar} from crossing file system boundaries when
+archiving. Use in conjunction with any write operation.
+@end table
+
+The @option{--one-file-system} option causes @command{tar} to modify its
+normal behavior in archiving the contents of directories. If a file in
+a directory is not on the same file system as the directory itself, then
+@command{tar} will not archive that file. If the file is a directory
+itself, @command{tar} will not archive anything beneath it; in other words,
+@command{tar} will not cross mount points.
+
+This option is useful for making full or incremental archival backups of
+a file system. If this option is used in conjunction with
+@option{--verbose} (@option{-v}), files that are excluded are
+mentioned by name on the standard error.
+
+@menu
+* directory:: Changing Directory
+* absolute:: Absolute File Names
+@end menu
+
+@node directory
+@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
+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
+@option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}).
+This will change the working directory to the specified directory
+after that point in the list.
+
+@table @option
+@opindex directory
+@item --directory=@var{directory}
+@itemx -C @var{directory}
+Changes the working directory in the middle of a command line.
+@end table
+
+For example,
+
+@smallexample
+$ @kbd{tar -c -f jams.tar grape prune -C food cherry}
+@end smallexample
+
+@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,
+
+@smallexample
+$ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
+@end smallexample
+
+@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 @option{--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}:
+
+@smallexample
+$ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
+@end smallexample
+
+@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 @option{--directory} options are interpreted consecutively. If
+@option{--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 @command{tar}, due to a previous
+@option{--directory} option.
+
+When using @option{--files-from} (@pxref{files}), you can put various
+@command{tar} options (including @option{-C}) in the file list. Notice,
+however, that in this case the option and its argument may not be
+separated by whitespace. If you use short option, its argument must
+either follow the option letter immediately, without any intervening
+whitespace, or occupy the next line. Otherwise, if you use long
+option, separate its argument by an equal sign.
+
+For instance, the file list for the above example will be:
+
+@smallexample
+@group
+-C/etc
+passwd
+hosts
+--directory=/lib
+libc.a
+@end group
+@end smallexample
+
+@noindent
+To use it, you would invoke @command{tar} as follows:
+
+@smallexample
+$ @kbd{tar -c -f foo.tar --files-from list}
+@end smallexample
+
+The interpretation of @option{--directory} is disabled by
+@option{--null} option.
+
+@node absolute
+@subsection Absolute File Names
+@UNREVISED
+
+@table @option
+@opindex absolute-names
+@item --absolute-names
+@itemx -P
+Do not strip leading slashes from file names, and permit file names
+containing a @file{..} file name component.
+@end table
+
+By default, @GNUTAR{} drops a leading @samp{/} on
+input or output, and complains about file names containing a @file{..}
+component. This option turns off this behavior.
+
+When @command{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}, @command{tar} will extract it as if the name were
+really @file{etc/passwd}.
+
+File names containing @file{..} can cause problems when extracting, so
+@command{tar} normally warns you about such files when creating an
+archive, and rejects attempts to extracts such files.
+
+Other @command{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-@GNUTAR{}
+program to use. Therefore, @GNUTAR{} also strips
+leading slashes from member names when putting members into the
+archive. For example, if you ask @command{tar} to add the file
+@file{/bin/ls} to an archive, it will do so, but the member name will
+be @file{bin/ls}.@footnote{A side effect of this is that when
+@option{--create} is used with @option{--verbose} the resulting output
+is not, generally speaking, the same as the one you'd get running
+@kbd{tar --list} command. This may be important if you use some
+scripts for comparing both outputs. @xref{listing member and file names},
+for the information on how to handle this case.}
+
+If you use the @option{--absolute-names} (@option{-P}) option,
+@command{tar} will do none of these transformations.
+
+To archive or extract files relative to the root directory, specify
+the @option{--absolute-names} (@option{-P}) option.
+
+Normally, @command{tar} acts on files relative to the working
+directory---ignoring superior directory names when archiving, and
+ignoring leading slashes when extracting.
+
+When you specify @option{--absolute-names} (@option{-P}),
+@command{tar} stores file names including all superior directory
+names, and preserves leading slashes. If you only invoked
+@command{tar} from the root directory you would never need the
+@option{--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 @option
+@item --absolute-names
+Preserves full file names (including superior directory names) when
+archiving files. Preserves leading slash when extracting files.
+
+@end table
+
+@FIXME{this is still horrible; need to talk with dan on monday.}
+
+@command{tar} prints out a message about removing the @samp{/} from
+file names. This message appears once per @GNUTAR{}
+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 @command{tar} standard
+error to the sink. For example, under @command{sh}:
+
+@smallexample
+$ @kbd{tar -c -f archive.tar /home 2> /dev/null}
+@end smallexample
+
+@noindent
+Another solution, both nicer and simpler, would be to change to
+the @file{/} directory first, and then avoid absolute notation.
+For example:
+
+@smallexample
+$ @kbd{tar -c -f archive.tar -C / home}
+@end smallexample
+
+@include getdate.texi
+
+@node Formats
+@chapter Controlling the Archive Format
+
+@cindex Tar archive formats
+Due to historical reasons, there are several formats of tar archives.
+All of them are based on the same principles, but have some subtle
+differences that often make them incompatible with each other.
+
+GNU tar is able to create and handle archives in a variety of formats.
+The most frequently used formats are (in alphabetical order):
+
+@table @asis
+@item gnu
+Format used by @GNUTAR{} versions up to 1.13.25. This format derived
+from an early @acronym{POSIX} standard, adding some improvements such as
+sparse file handling and incremental archives. Unfortunately these
+features were implemented in a way incompatible with other archive
+formats.
+
+Archives in @samp{gnu} format are able to hold file names of unlimited
+length.
+
+@item oldgnu
+Format used by @GNUTAR{} of versions prior to 1.12.
+
+@item v7
+Archive format, compatible with the V7 implementation of tar. This
+format imposes a number of limitations. The most important of them
+are:
+
+@enumerate
+@item The maximum length of a file name is limited to 99 characters.
+@item The maximum length of a symbolic link is limited to 99 characters.
+@item It is impossible to store special files (block and character
+devices, fifos etc.)
+@item Maximum value of user or group @acronym{ID} is limited to 2097151 (7777777
+octal)
+@item V7 archives do not contain symbolic ownership information (user
+and group name of the file owner).
+@end enumerate
+
+This format has traditionally been used by Automake when producing
+Makefiles. This practice will change in the future, in the meantime,
+however this means that projects containing file names more than 99
+characters long will not be able to use @GNUTAR{} @value{VERSION} and
+Automake prior to 1.9.
+
+@item ustar
+Archive format defined by @acronym{POSIX.1-1988} specification. It stores
+symbolic ownership information. It is also able to store
+special files. However, it imposes several restrictions as well:
+
+@enumerate
+@item The maximum length of a file name is limited to 256 characters,
+provided that the file name can be split at a directory separator in
+two parts, first of them being at most 155 bytes long. So, in most
+cases the maximum file name length will be shorter than 256
+characters.
+@item The maximum length of a symbolic link name is limited to
+100 characters.
+@item Maximum size of a file the archive is able to accommodate
+is 8GB
+@item Maximum value of UID/GID is 2097151.
+@item Maximum number of bits in device major and minor numbers is 21.
+@end enumerate
+
+@item star
+Format used by J@"org Schilling @command{star}
+implementation. @GNUTAR{} is able to read @samp{star} archives but
+currently does not produce them.
+
+@item posix
+Archive format defined by @acronym{POSIX.1-2001} specification. This is the
+most flexible and feature-rich format. It does not impose any
+restrictions on file sizes or file name lengths. This format is quite
+recent, so not all tar implementations are able to handle it properly.
+However, this format is designed in such a way that any tar
+implementation able to read @samp{ustar} archives will be able to read
+most @samp{posix} archives as well, with the only exception that any
+additional information (such as long file names etc.) will in such
+case be extracted as plain text files along with the files it refers to.
+
+This archive format will be the default format for future versions
+of @GNUTAR{}.
+
+@end table
+
+The following table summarizes the limitations of each of these
+formats:
+
+@multitable @columnfractions .10 .20 .20 .20 .20
+@headitem Format @tab UID @tab File Size @tab File Name @tab Devn
+@item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
+@item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
+@item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
+@item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
+@item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
+@end multitable
+
+The default format for @GNUTAR{} is defined at compilation
+time. You may check it by running @command{tar --help}, and examining
+the last lines of its output. Usually, @GNUTAR{} is configured
+to create archives in @samp{gnu} format, however, future version will
+switch to @samp{posix}.
+
+@menu
+* Compression:: Using Less Space through Compression
+* Attributes:: Handling File Attributes
+* Portability:: Making @command{tar} Archives More Portable
+* cpio:: Comparison of @command{tar} and @command{cpio}
+@end menu
+
+@node Compression
+@section Using Less Space through Compression
+
+@menu
+* gzip:: Creating and Reading Compressed Archives
+* sparse:: Archiving Sparse Files
+@end menu
+
+@node gzip
+@subsection Creating and Reading Compressed Archives
+@cindex Compressed archives
+@cindex Storing archives in compressed format
+
+@cindex gzip
+@cindex bzip2
+@cindex lzma
+@cindex lzop
+@cindex compress
+@GNUTAR{} is able to create and read compressed archives. It supports
+@command{gzip}, @command{bzip2}, @command{lzma} and @command{lzop} compression
+programs. For backward compatibility, it also supports
+@command{compress} command, although we strongly recommend against
+using it, because it is by far less effective than other compression
+programs@footnote{It also had patent problems in the past.}.
+
+Creating a compressed archive is simple: you just specify a
+@dfn{compression option} along with the usual archive creation
+commands. The compression option is @option{-z} (@option{--gzip}) to
+create a @command{gzip} compressed archive, @option{-j}
+(@option{--bzip2}) to create a @command{bzip2} compressed archive,
+@option{-J} (@option{--lzma}) to create an @asis{LZMA} compressed
+archive, @option{--lzop} to create an @asis{LSOP} archive, and
+@option{-Z} (@option{--compress}) to use @command{compress} program.
+For example:
+
+@smallexample
+$ @kbd{tar cfz archive.tar.gz .}
+@end smallexample
+
+You can also let @GNUTAR{} select the compression program basing on
+the suffix of the archive file name. This is done using
+@option{--auto-compress} (@option{-a}) command line option. For
+example, the following invocation will use @command{bzip2} for
+compression:
+
+@smallexample
+$ @kbd{tar cfa archive.tar.bz2 .}
+@end smallexample
+
+@noindent
+whereas the following one will use @command{lzma}:
+
+@smallexample
+$ @kbd{tar cfa archive.tar.lzma .}
+@end smallexample
+
+For a complete list of file name suffixes recognized by @GNUTAR{},
+@ref{auto-compress}.
+
+Reading compressed archive is even simpler: you don't need to specify
+any additional options as @GNUTAR{} recognizes its format
+automatically. Thus, the following commands will list and extract the
+archive created in previous example:
+
+@smallexample
+# List the compressed archive
+$ @kbd{tar tf archive.tar.gz}
+# Extract the compressed archive
+$ @kbd{tar xf archive.tar.gz}
+@end smallexample
+
+The format recognition algorithm is based on @dfn{signatures}, a
+special byte sequences in the beginning of file, that are specific for
+certain compression formats. If this approach fails, @command{tar}
+falls back to using archive name suffix to determine its format
+(@xref{auto-compress}, for a list of recognized suffixes).
+
+The only case when you have to specify a decompression option while
+reading the archive is when reading from a pipe or from a tape drive
+that does not support random access. However, in this case @GNUTAR{}
+will indicate which option you should use. For example:
+
+@smallexample
+$ @kbd{cat archive.tar.gz | tar tf -}
+tar: Archive is compressed. Use -z option
+tar: Error is not recoverable: exiting now
+@end smallexample
+
+If you see such diagnostics, just add the suggested option to the
+invocation of @GNUTAR{}:
+
+@smallexample
+$ @kbd{cat archive.tar.gz | tar tfz -}
+@end smallexample
+
+Notice also, that there are several restrictions on operations on
+compressed archives. First of all, compressed archives cannot be
+modified, i.e., you cannot update (@option{--update} (@option{-u}))
+them or delete (@option{--delete}) members from them or
+add (@option{--append} (@option{-r})) members to them. Likewise, you
+cannot append another @command{tar} archive to a compressed archive using
+@option{--concatenate} (@option{-A})). Secondly, multi-volume
+archives cannot be compressed.
+
+The following table summarizes compression options used by @GNUTAR{}.
+
+@table @option
+@anchor{auto-compress}
+@opindex auto-compress
+@item --auto-compress
+@itemx -a
+Select a compression program to use by the archive file name
+suffix. The following suffixes are recognized:
+
+@multitable @columnfractions 0.3 0.6
+@headitem Suffix @tab Compression program
+@item @samp{.gz} @tab @command{gzip}
+@item @samp{.tgz} @tab @command{gzip}
+@item @samp{.taz} @tab @command{gzip}
+@item @samp{.Z} @tab @command{compress}
+@item @samp{.taZ} @tab @command{compress}
+@item @samp{.bz2} @tab @command{bzip2}
+@item @samp{.tz2} @tab @command{bzip2}
+@item @samp{.tbz2} @tab @command{bzip2}
+@item @samp{.tbz} @tab @command{bzip2}
+@item @samp{.lzma} @tab @command{lzma}
+@item @samp{.tlz} @tab @command{lzma}
+@item @samp{.lzo} @tab @command{lzop}
+@end multitable
+
+@opindex gzip
+@opindex ungzip
+@item -z
+@itemx --gzip
+@itemx --ungzip
+Filter the archive through @command{gzip}.
+
+You can use @option{--gzip} and @option{--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 @command{tar} program to enforce the specified (or default) record
+size. The default compression parameters are used; if you need to
+override them, set @env{GZIP} environment variable, e.g.:
+
+@smallexample
+$ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
+@end smallexample
+
+@noindent
+Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
+@command{gzip} explicitly:
+
+@smallexample
+$ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
+@end smallexample
+
+@cindex corrupted archives
+About corrupted compressed archives: @command{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 unsynchronized, 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 @GNUTAR{}. 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
+lose some compressibility. But this would have make recovering easier.
+So, there are pros and cons. We'll see!
+
+@opindex bzip2
+@item -j
+@itemx --bzip2
+Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
+
+@opindex lzma
+@item --lzma
+@itemx -J
+Filter the archive through @command{lzma}. Otherwise like @option{--gzip}.
+
+@opindex lzop
+@item --lzop
+Filter the archive through @command{lzop}. Otherwise like
+@option{--gzip}.
+
+@opindex compress
+@opindex uncompress
+@item -Z
+@itemx --compress
+@itemx --uncompress
+Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
+
+@opindex use-compress-program
+@item --use-compress-program=@var{prog}
+@itemx -I=@var{prog}
+Use external compression program @var{prog}. Use this option if you
+have a compression program that @GNUTAR{} does not support. There
+are two requirements to which @var{prog} should comply:
+
+First, when called without options, it should read data from standard
+input, compress it and output it on standard output.
+
+Secondly, if called with @option{-d} argument, it should do exactly
+the opposite, i.e., read the compressed data from the standard input
+and produce uncompressed data on the standard output.
+@end table
+
+@cindex gpg, using with tar
+@cindex gnupg, using with tar
+@cindex Using encrypted archives
+The @option{--use-compress-program} option, in particular, lets you
+implement your own filters, not necessarily dealing with
+compression/decompression. For example, suppose you wish to implement
+PGP encryption on top of compression, using @command{gpg} (@pxref{Top,
+gpg, gpg ---- encryption and signing tool, gpg, GNU Privacy Guard
+Manual}). The following script does that:
+
+@smallexample
+@group
+#! /bin/sh
+case $1 in
+-d) gpg --decrypt - | gzip -d -c;;
+'') gzip -c | gpg -s ;;
+*) echo "Unknown option $1">&2; exit 1;;
+esac
+@end group
+@end smallexample
+
+Suppose you name it @file{gpgz} and save it somewhere in your
+@env{PATH}. Then the following command will create a compressed
+archive signed with your private key:
+
+@smallexample
+$ @kbd{tar -cf foo.tar.gpgz -Igpgz .}
+@end smallexample
+
+@noindent
+Likewise, the command below will list its contents:
+
+@smallexample
+$ @kbd{tar -tf foo.tar.gpgz -Igpgz .}
+@end smallexample
+
+@ignore
+The above is based on the following discussion:
+
+ 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 @option{--gzip}, but I'd also like
+ the output to be fed through a program like @acronym{GNU}
+ @command{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 @command{tar} through @command{ecc}, but then I lose (though I
+ haven't started using it yet, I confess) the ability to have
+ @command{tar} use @command{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 @command{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 (apparently) 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
+ @option{--use-compress-prog=@var{program}} 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 @option{-d} option, for when
+ extraction is needed rather than creation.
+
+ It has been reported that if one writes compressed data (through the
+ @option{--gzip} or @option{--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.
+@end ignore
+
+@node sparse
+@subsection Archiving Sparse Files
+@cindex Sparse Files
+
+Files in the file system occasionally have @dfn{holes}. A @dfn{hole}
+in a file is a section of the file's contents which was never written.
+The contents of a hole reads 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, @command{tar}
+could create an archive longer than the original. To have @command{tar}
+attempt to recognize the holes in a file, use @option{--sparse}
+(@option{-S}). When you use this option, then, for any file using
+less disk space than would be expected from its length, @command{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 @option{--sparse} is not needed on extraction) any
+such files have holes created wherever the continuous stretches of zeros
+were found. Thus, if you use @option{--sparse}, @command{tar} archives
+won't take more space than the original.
+
+@table @option
+@opindex sparse
+@item -S
+@itemx --sparse
+This option instructs @command{tar} to test each file for sparseness
+before attempting to archive it. If the file is found to be sparse it
+is treated specially, thus allowing to decrease the amount of space
+used by its image in the archive.
+
+This option is meaningful only when creating or updating archives. It
+has no effect on extraction.
+@end table
+
+Consider using @option{--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 @option{--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). @xref{Incremental Dumps}.
+
+However, be aware that @option{--sparse} option presents a serious
+drawback. Namely, in order to determine if the file is sparse
+@command{tar} has to read it before trying to archive it, so in total
+the file is read @strong{twice}. So, always bear in mind that the
+time needed to process all files with this option is roughly twice
+the time needed to archive them without it.
+@FIXME{A technical note:
+
+Programs like @command{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.
+@GNUTAR{} 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
+}
+
+@cindex sparse formats, defined
+When using @samp{POSIX} archive format, @GNUTAR{} is able to store
+sparse files using in three distinct ways, called @dfn{sparse
+formats}. A sparse format is identified by its @dfn{number},
+consisting, as usual of two decimal numbers, delimited by a dot. By
+default, format @samp{1.0} is used. If, for some reason, you wish to
+use an earlier format, you can select it using
+@option{--sparse-version} option.
+
+@table @option
+@opindex sparse-version
+@item --sparse-version=@var{version}
+
+Select the format to store sparse files in. Valid @var{version} values
+are: @samp{0.0}, @samp{0.1} and @samp{1.0}. @xref{Sparse Formats},
+for a detailed description of each format.
+@end table
+
+Using @option{--sparse-format} option implies @option{--sparse}.
+
+@node Attributes
+@section Handling File Attributes
+@UNREVISED
+
+When @command{tar} reads files, it updates their access times. To
+avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
+reset the access time retroactively or avoid changing it in the first
+place.
+
+Handling of file attributes
+
+@table @option
+@opindex atime-preserve
+@item --atime-preserve
+@itemx --atime-preserve=replace
+@itemx --atime-preserve=system
+Preserve the access times of files that are read. This works only for
+files that you own, unless you have superuser privileges.
+
+@option{--atime-preserve=replace} works on most systems, but it also
+restores the data modification time and updates the status change
+time. Hence it doesn't interact with incremental dumps nicely
+(@pxref{Incremental Dumps}), and it can set access or data modification times
+incorrectly if other programs access the file while @command{tar} is
+running.
+
+@option{--atime-preserve=system} avoids changing the access time in
+the first place, if the operating system supports this.
+Unfortunately, this may or may not work on any given operating system
+or file system. If @command{tar} knows for sure it won't work, it
+complains right away.
+
+Currently @option{--atime-preserve} with no operand defaults to
+@option{--atime-preserve=replace}, but this is intended to change to
+@option{--atime-preserve=system} when the latter is better-supported.
+
+@opindex touch
+@item -m
+@itemx --touch
+Do not extract data modification time.
+
+When this option is used, @command{tar} leaves the data modification times
+of the files it extracts as the times when the files were extracted,
+instead of setting it to the times recorded in the archive.
+
+This option is meaningless with @option{--list} (@option{-t}).
+
+@opindex same-owner
+@item --same-owner
+Create extracted files with the same ownership they have in the
+archive.
+
+This is the default behavior for the superuser,
+so this option is meaningful only for non-root users, when @command{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, @command{tar} writes the user @acronym{ID} and user name
+separately. If it can't find a user name (because the user @acronym{ID} is not
+in @file{/etc/passwd}), then it does not write one. When restoring,
+it tries to look the name (if one was written) up in
+@file{/etc/passwd}. If it fails, then it uses the user @acronym{ID} stored in
+the archive instead.
+
+@opindex no-same-owner
+@item --no-same-owner
+@itemx -o
+Do not attempt to restore ownership when extracting. This is the
+default behavior for ordinary users, so this option has an effect
+only for the superuser.
+
+@opindex numeric-owner
+@item --numeric-owner
+The @option{--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 file system(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 @command{tar} archives.
+The identifying names are added at create time when provided by the
+system, unless @option{--old-archive} (@option{-o}) 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 @command{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
+@command{tar} archive out of this directory, before cleaning
+everything out. Of course, we could add a lot of options to
+@GNUTAR{} for fine tuning permissions and ownership.
+This is not the good way, I think. @GNUTAR{} is
+already crowded with options and moreover, the approach just explained
+gives you a great deal of control already.
+
+@xopindex{same-permissions, short description}
+@xopindex{preserve-permissions, short description}
+@item -p
+@itemx --same-permissions
+@itemx --preserve-permissions
+Extract all protection information.
+
+This option causes @command{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 by default enabled when
+@command{tar} is executed by a superuser.
+
+
+This option is meaningless with @option{--list} (@option{-t}).
+
+@opindex preserve
+@item --preserve
+Same as both @option{--same-permissions} and @option{--same-order}.
+
+The @option{--preserve} option has no equivalent short option name.
+It is equivalent to @option{--same-permissions} plus @option{--same-order}.
+
+@FIXME{I do not see the purpose of such an option. (Neither I. FP.)
+Neither do I. --Sergey}
+
+@end table
+
+@node Portability
+@section Making @command{tar} Archives More Portable
+
+Creating a @command{tar} archive on a particular system that is meant to be
+useful later on many other machines and with other versions of @command{tar}
+is more challenging than you might think. @command{tar} archive formats
+have been evolving since the first versions of Unix. Many such formats
+are around, and are not always compatible with each other. This section
+discusses a few problems, and gives some advice about making @command{tar}
+archives more portable.
+
+One golden rule is simplicity. For example, limit your @command{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.
+
+@FIXME{Discuss GNU extensions (incremental backups, multi-volume
+archives and archive labels) in GNU and PAX formats.}
+
+@menu
+* Portable Names:: Portable Names
+* dereference:: Symbolic Links
+* hard links:: Hard Links
+* old:: Old V7 Archives
+* ustar:: Ustar Archives
+* gnu:: GNU and old GNU format archives.
+* posix:: @acronym{POSIX} archives
+* Checksumming:: Checksumming Problems
+* Large or Negative Values:: Large files, negative time stamps, etc.
+* Other Tars:: How to Extract GNU-Specific Data Using
+ Other @command{tar} Implementations
+@end menu
+
+@node Portable Names
+@subsection Portable Names
+
+Use portable file and member names. A name is portable if it contains
+only @acronym{ASCII} letters and digits, @samp{/}, @samp{.}, @samp{_}, and
+@samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or
+contain @samp{/-}. Avoid deep directory nesting. For portability to
+old Unix hosts, limit your file name components to 14 characters or
+less.
+
+If you intend to have your @command{tar} archives to be read under
+MSDOS, you should not rely on case distinction for file names, and you
+might use the @acronym{GNU} @command{doschk} program for helping you
+further diagnosing illegal MSDOS names, which are even more limited
+than System V's.
+
+@node dereference
+@subsection Symbolic Links
+@cindex File names, using symbolic links
+@cindex Symbolic link as file name
+
+@opindex dereference
+Normally, when @command{tar} archives a symbolic link, it writes a
+block to the archive naming the target of the link. In that way, the
+@command{tar} archive is a faithful record of the file system contents.
+@option{--dereference} (@option{-h}) is used with @option{--create} (@option{-c}), and causes
+@command{tar} to archive the files symbolic links point to, instead of
+the links themselves. When this option is used, when @command{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 @command{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 @command{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 @option{--dereference} (@option{-h}): many systems do not support
+symbolic links, and moreover, your distribution might be unusable if
+it contains unresolved symbolic links.
+
+@node hard links
+@subsection Hard Links
+@UNREVISED{}
+@cindex File names, using hard links
+@cindex hard links, dereferencing
+@cindex dereferencing hard links
+
+Normally, when @command{tar} archives a hard link, it writes a
+block to the archive naming the target of the link (a @samp{1} type
+block). In that way, the actual file contents is stored in file only
+once. For example, consider the following two files:
+
+@smallexample
+@group
+$ ls
+-rw-r--r-- 2 gray staff 4 2007-10-30 15:11 one
+-rw-r--r-- 2 gray staff 4 2007-10-30 15:11 jeden
+@end group
+@end smallexample
+
+Here, @file{jeden} is a link to @file{one}. When archiving this
+directory with a verbose level 2, you will get an output similar to
+the following:
+
+@smallexample
+$ tar cfvv ../archive.tar .
+drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
+-rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
+hrw-r--r-- gray/staff 0 2007-10-30 15:11 ./one link to ./jeden
+@end smallexample
+
+The last line shows that, instead of storing two copies of the file,
+@command{tar} stored it only once, under the name @file{jeden}, and
+stored file @file{one} as a hard link to this file.
+
+It may be important to know that all hard links to the given file are
+stored in the archive. For example, this may be necessary for exact
+reproduction of the file system. The following option does that:
+
+@table @option
+@xopindex{check-links, described}
+@item --check-links
+@itemx -l
+Check the number of links dumped for each processed file. If this
+number does not match the total number of hard links for the file, print
+a warning message.
+@end table
+
+For example, trying to archive only file @file{jeden} with this option
+produces the following diagnostics:
+
+@smallexample
+$ tar -c -f ../archive.tar jeden
+tar: Missing links to `jeden'.
+@end smallexample
+
+Although creating special records for hard links helps keep a faithful
+record of the file system contents and makes archives more compact, it
+may present some difficulties when extracting individual members from
+the archive. For example, trying to extract file @file{one} from the
+archive created in previous examples produces, in the absense of file
+@file{jeden}:
+
+@smallexample
+$ tar xf archive.tar ./one
+tar: ./one: Cannot hard link to `./jeden': No such file or directory
+tar: Error exit delayed from previous errors
+@end smallexample
+
+The reason for this behavior is that @command{tar} cannot seek back in
+the archive to the previous member (in this case, @file{one}), to
+extract it@footnote{There are plans to fix this in future releases.}.
+If you wish to avoid such problems at the cost of a bigger archive,
+use the following option:
+
+@table @option
+@xopindex{hard-dereference, described}
+@item --hard-dereference
+Dereference hard links and store the files they refer to.
+@end table
+
+For example, trying this option on our two sample files, we get two
+copies in the archive, each of which can then be extracted
+independently of the other:
+
+@smallexample
+@group
+$ tar -c -vv -f ../archive.tar --hard-dereference .
+drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
+-rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
+-rw-r--r-- gray/staff 4 2007-10-30 15:11 ./one
+@end group
+@end smallexample
+
+@node old
+@subsection Old V7 Archives
+@cindex Format, old style
+@cindex Old style format
+@cindex Old style archives
+@cindex v7 archive format
+
+Certain old versions of @command{tar} cannot handle additional
+information recorded by newer @command{tar} programs. To create an
+archive in V7 format (not ANSI), which can be read by these old
+versions, specify the @option{--format=v7} option in
+conjunction with the @option{--create} (@option{-c}) (@command{tar} also
+accepts @option{--portability} or @option{--old-archive} for this
+option). When you specify it,
+@command{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 @option{--format=v7}
+unless the archive was created using this option.
+
+In most cases, a @emph{new} format archive can be read by an @emph{old}
+@command{tar} program without serious trouble, so this option should
+seldom be needed. On the other hand, most modern @command{tar}s are
+able to read old format archives, so it might be safer for you to
+always use @option{--format=v7} for your distributions. Notice,
+however, that @samp{ustar} format is a better alternative, as it is
+free from many of @samp{v7}'s drawbacks.
-@GNUTAR{} compute checksums both ways, and accept
-any on read, so @acronym{GNU} tar can read Sun tapes even with their
-wrong checksums. @GNUTAR{} produces the standard
-checksum, however, raising incompatibilities with Sun. That is to
-say, @GNUTAR{} has not been modified to
-@emph{produce} incorrect archives to be read by buggy @command{tar}'s.
-I've been told that more recent Sun @command{tar} now read standard
-archives, so maybe Sun did a similar patch, after all?
+@node ustar
+@subsection Ustar Archive Format
-The story seems to be that when Sun first imported @command{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 @command{tar} archives to be compatible with Sun's.
-The current standards do not favor Sun @command{tar} format. In any
-case, it now falls on the shoulders of SunOS and HP-UX users to get
-a @command{tar} able to read the good archives they receive.
+@cindex ustar archive format
+Archive format defined by @acronym{POSIX}.1-1988 specification is called
+@code{ustar}. Although it is more flexible than the V7 format, it
+still has many restrictions (@xref{Formats,ustar}, for the detailed
+description of @code{ustar} format). Along with V7 format,
+@code{ustar} format is a good choice for archives intended to be read
+with other implementations of @command{tar}.
-@node Large or Negative Values
-@subsection Large or Negative Values
-@cindex large values
-@cindex future time stamps
-@cindex negative time stamps
-@UNREVISED{}
+To create archive in @code{ustar} format, use @option{--format=ustar}
+option in conjunction with the @option{--create} (@option{-c}).
-The above sections suggest to use @samp{oldest possible} archive
-format if in doubt. However, sometimes it is not possible. If you
-attempt to archive a file whose metadata cannot be represented using
-required format, @GNUTAR{} will print error message and ignore such a
-file. You will than have to switch to a format that is able to
-handle such values. The format summary table (@pxref{Formats}) will
-help you to do so.
+@node gnu
+@subsection @acronym{GNU} and old @GNUTAR{} format
-In particular, when trying to archive files larger than 8GB or with
-timestamps not in the range 1970-01-01 00:00:00 through 2242-03-16
-12:56:31 @sc{utc}, you will have to chose between @acronym{GNU} and
-@acronym{POSIX} archive formats. When considering which format to
-choose, bear in mind that the @acronym{GNU} format uses
-two's-complement base-256 notation to store values that do not fit
-into standard @acronym{ustar} range. Such archives can generally be
-read only by a @GNUTAR{} implementation. Moreover, they sometimes
-cannot be correctly restored on another hosts even by @GNUTAR{}. For
-example, using two's complement representation for negative time
-stamps that assumes a signed 32-bit @code{time_t} generates archives
-that are not portable to hosts with differing @code{time_t}
-representations.
+@cindex GNU archive format
+@cindex Old GNU archive format
+@GNUTAR{} was based on an early draft of the
+@acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
+@command{tar}, such as the support for file names longer than 100
+characters, use portions of the @command{tar} header record which were
+specified in that @acronym{POSIX} draft as unused. Subsequent changes in
+@acronym{POSIX} have allocated the same parts of the header record for
+other purposes. As a result, @GNUTAR{} format is
+incompatible with the current @acronym{POSIX} specification, and with
+@command{tar} programs that follow it.
-On the other hand, @acronym{POSIX} archives, generally speaking, can
-be extracted by any tar implementation that understands older
-@acronym{ustar} format. The only exception are files larger than 8GB.
+In the majority of cases, @command{tar} will be configured to create
+this format by default. This will change in future releases, since
+we plan to make @samp{POSIX} format the default.
-@FIXME{Describe how @acronym{POSIX} archives are extracted by non
-POSIX-aware tars.}
+To force creation a @GNUTAR{} archive, use option
+@option{--format=gnu}.
-@node Compression
-@section Using Less Space through Compression
+@node posix
+@subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
+
+@cindex POSIX archive format
+@cindex PAX archive format
+Starting from version 1.14 @GNUTAR{} features full support for
+@acronym{POSIX.1-2001} archives.
+
+A @acronym{POSIX} conformant archive will be created if @command{tar}
+was given @option{--format=posix} (@option{--format=pax}) option. No
+special option is required to read and extract from a @acronym{POSIX}
+archive.
@menu
-* gzip:: Creating and Reading Compressed Archives
-* sparse:: Archiving Sparse Files
+* PAX keywords:: Controlling Extended Header Keywords.
@end menu
-@node gzip
-@subsection Creating and Reading Compressed Archives
-@cindex Compressed archives
-@cindex Storing archives in compressed format
+@node PAX keywords
+@subsubsection Controlling Extended Header Keywords
-@GNUTAR{} is able to create and read compressed archives. It supports
-@command{gzip} and @command{bzip2} compression programs. For backward
-compatibilty, it also supports @command{compress} command, although
-we strongly recommend against using it, since there is a patent
-covering the algorithm it uses and you could be sued for patent
-infringement merely by running @command{compress}! Besides, it is less
-effective than @command{gzip} and @command{bzip2}.
+@table @option
+@opindex pax-option
+@item --pax-option=@var{keyword-list}
+Handle keywords in @acronym{PAX} extended headers. This option is
+equivalent to @option{-o} option of the @command{pax} utility.
+@end table
-Creating a compressed archive is simple: you just specify a
-@dfn{compression option} along with the usual archive creation
-commands. The compression option is @option{-z} (@option{--gzip}) to
-create a @command{gzip} compressed archive, @option{-j}
-(@option{--bzip2}) to create a @command{bzip2} compressed archive, and
-@option{-Z} (@option{--compress}) to use @command{compress} program.
-For example:
+@var{Keyword-list} is a comma-separated
+list of keyword options, each keyword option taking one of
+the following forms:
-@smallexample
-$ @kbd{tar cfz archive.tar.gz .}
-@end smallexample
+@table @code
+@item delete=@var{pattern}
+When used with one of archive-creation commands,
+this option instructs @command{tar} to omit from extended header records
+that it produces any keywords matching the string @var{pattern}.
-Reading compressed archive is even simpler: you don't need to specify
-any additional options as @GNUTAR{} recognizes its format
-automatically. Thus, the following commands will list and extract the
-archive created in previous example:
+When used in extract or list mode, this option instructs tar
+to ignore any keywords matching the given @var{pattern} in the extended
+header records. In both cases, matching is performed using the pattern
+matching notation described in @acronym{POSIX 1003.2}, 3.13
+(@pxref{wildcards}). For example:
@smallexample
-# List the compressed archive
-$ @kbd{tar tf archive.tar.gz}
-# Extract the compressed archive
-$ @kbd{tar xf archive.tar.gz}
+--pax-option delete=security.*
@end smallexample
-The only case when you have to specify a decompression option while
-reading the archive is when reading from a pipe or from a tape drive
-that does not support random access. However, in this case @GNUTAR{}
-will indicate which option you should use. For example:
+would suppress security-related information.
-@smallexample
-$ @kbd{cat archive.tar.gz | tar tf -}
-tar: Archive is compressed. Use -z option
-tar: Error is not recoverable: exiting now
-@end smallexample
+@item exthdr.name=@var{string}
-If you see such diagnostics, just add the suggested option to the
-invocation of @GNUTAR{}:
+This keyword allows user control over the name that is written into the
+ustar header blocks for the extended headers. The name is obtained
+from @var{string} after making the following substitutions:
+
+@multitable @columnfractions .25 .55
+@headitem Meta-character @tab Replaced By
+@item %d @tab The directory name of the file, equivalent to the
+result of the @command{dirname} utility on the translated file name.
+@item %f @tab The name of the file with the directory information
+stripped, equivalent to the result of the @command{basename} utility
+on the translated file name.
+@item %p @tab The process @acronym{ID} of the @command{tar} process.
+@item %% @tab A @samp{%} character.
+@end multitable
+
+Any other @samp{%} characters in @var{string} produce undefined
+results.
+
+If no option @samp{exthdr.name=string} is specified, @command{tar}
+will use the following default value:
@smallexample
-$ @kbd{cat archive.tar.gz | tar tfz -}
+%d/PaxHeaders.%p/%f
@end smallexample
-Notice also, that there are several restrictions on operations on
-compressed archives. First of all, compressed archives cannot be
-modified, i.e., you cannot update (@option{--update} (@option{-u})) them or delete
-(@option{--delete}) members from them. Likewise, you cannot append
-another @command{tar} archive to a compressed archive using
-@option{--append} (@option{-r})). Secondly, multi-volume archives cannot be
-compressed.
+@item globexthdr.name=@var{string}
+This keyword allows user control over the name that is written into
+the ustar header blocks for global extended header records. The name
+is obtained from the contents of @var{string}, after making
+the following substitutions:
-The following table summarizes compression options used by @GNUTAR{}.
+@multitable @columnfractions .25 .55
+@headitem Meta-character @tab Replaced By
+@item %n @tab An integer that represents the
+sequence number of the global extended header record in the archive,
+starting at 1.
+@item %p @tab The process @acronym{ID} of the @command{tar} process.
+@item %% @tab A @samp{%} character.
+@end multitable
-@table @option
-@opindex gzip
-@opindex ungzip
-@item -z
-@itemx --gzip
-@itemx --ungzip
-Filter the archive through @command{gzip}.
+Any other @samp{%} characters in @var{string} produce undefined results.
-You can use @option{--gzip} and @option{--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 @command{tar} program to enforce the specified (or default) record
-size. The default compression parameters are used; if you need to
-override them, set @env{GZIP} environment variable, e.g.:
+If no option @samp{globexthdr.name=string} is specified, @command{tar}
+will use the following default value:
@smallexample
-$ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
+$TMPDIR/GlobalHead.%p.%n
@end smallexample
@noindent
-Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
-@command{gzip} explicitly:
+where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
+environment variable. If @var{TMPDIR} is not set, @command{tar}
+uses @samp{/tmp}.
+
+@item @var{keyword}=@var{value}
+When used with one of archive-creation commands, these keyword/value pairs
+will be included at the beginning of the archive in a global extended
+header record. When used with one of archive-reading commands,
+@command{tar} will behave as if it has encountered these keyword/value
+pairs at the beginning of the archive in a global extended header
+record.
+
+@item @var{keyword}:=@var{value}
+When used with one of archive-creation commands, these keyword/value pairs
+will be included as records at the beginning of an extended header for
+each file. This is effectively equivalent to @var{keyword}=@var{value}
+form except that it creates no global extended header records.
+
+When used with one of archive-reading commands, @command{tar} will
+behave as if these keyword/value pairs were included as records at the
+end of each extended header; thus, they will override any global or
+file-specific extended header record keywords of the same names.
+For example, in the command:
@smallexample
-$ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
+tar --format=posix --create \
+ --file archive --pax-option gname:=user .
@end smallexample
-@cindex corrupted archives
-About corrupted compressed archives: @command{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 unsynchronized, and there
-is little chance that you could recover later in the archive.
+the group name will be forced to a new value for all files
+stored in the archive.
+@end table
-There are pending suggestions for having a per-volume or per-file
-compression in @GNUTAR{}. 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
-lose some compressibility. But this would have make recovering easier.
-So, there are pros and cons. We'll see!
+@node Checksumming
+@subsection Checksumming Problems
-@opindex bzip2
-@item -j
-@itemx --bzip2
-Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
+SunOS and HP-UX @command{tar} fail to accept archives created using
+@GNUTAR{} and containing non-@acronym{ASCII} file names, that
+is, file names having characters with the eight bit set, because they
+use signed checksums, while @GNUTAR{} uses unsigned
+checksums while creating archives, as per @acronym{POSIX} standards. On
+reading, @GNUTAR{} 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.
-@opindex compress
-@opindex uncompress
-@item -Z
-@itemx --compress
-@itemx --uncompress
-Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
+@GNUTAR{} compute checksums both ways, and accept
+any on read, so @acronym{GNU} tar can read Sun tapes even with their
+wrong checksums. @GNUTAR{} produces the standard
+checksum, however, raising incompatibilities with Sun. That is to
+say, @GNUTAR{} has not been modified to
+@emph{produce} incorrect archives to be read by buggy @command{tar}'s.
+I've been told that more recent Sun @command{tar} now read standard
+archives, so maybe Sun did a similar patch, after all?
-The @acronym{GNU} Project recommends you not use
-@command{compress}, because there is a patent covering the algorithm it
-uses. You could be sued for patent infringement merely by running
-@command{compress}.
+The story seems to be that when Sun first imported @command{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 @command{tar} archives to be compatible with Sun's.
+The current standards do not favor Sun @command{tar} format. In any
+case, it now falls on the shoulders of SunOS and HP-UX users to get
+a @command{tar} able to read the good archives they receive.
-@opindex use-compress-program
-@item --use-compress-program=@var{prog}
-Use external compression program @var{prog}. Use this option if you
-have a compression program that @GNUTAR{} does not support. There
-are two requirements to which @var{prog} should comply:
+@node Large or Negative Values
+@subsection Large or Negative Values
+@cindex large values
+@cindex future time stamps
+@cindex negative time stamps
+@UNREVISED{}
-First, when called without options, it should read data from standard
-input, compress it and output it on standard output.
+The above sections suggest to use @samp{oldest possible} archive
+format if in doubt. However, sometimes it is not possible. If you
+attempt to archive a file whose metadata cannot be represented using
+required format, @GNUTAR{} will print error message and ignore such a
+file. You will than have to switch to a format that is able to
+handle such values. The format summary table (@pxref{Formats}) will
+help you to do so.
-Secondly, if called with @option{-d} argument, it should do exactly
-the opposite, i.e., read the compressed data from the standard input
-and produce uncompressed data on the standard output.
-@end table
+In particular, when trying to archive files larger than 8GB or with
+timestamps not in the range 1970-01-01 00:00:00 through 2242-03-16
+12:56:31 @sc{utc}, you will have to chose between @acronym{GNU} and
+@acronym{POSIX} archive formats. When considering which format to
+choose, bear in mind that the @acronym{GNU} format uses
+two's-complement base-256 notation to store values that do not fit
+into standard @acronym{ustar} range. Such archives can generally be
+read only by a @GNUTAR{} implementation. Moreover, they sometimes
+cannot be correctly restored on another hosts even by @GNUTAR{}. For
+example, using two's complement representation for negative time
+stamps that assumes a signed 32-bit @code{time_t} generates archives
+that are not portable to hosts with differing @code{time_t}
+representations.
-@FIXME{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 @option{--gzip}, but I'd also like
-the output to be fed through a program like @acronym{GNU}
-@command{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 @command{tar} through @command{ecc}, but then I lose (though I
-haven't started using it yet, I confess) the ability to have
-@command{tar} use @command{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 @command{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 (apparently) 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 @option{--use-compress-prog=@var{program}} 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 @option{-d} option, for when
-extraction is needed rather than creation.
-
-It has been reported that if one writes compressed data (through the
-@option{--gzip} or @option{--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.}
+On the other hand, @acronym{POSIX} archives, generally speaking, can
+be extracted by any tar implementation that understands older
+@acronym{ustar} format. The only exception are files larger than 8GB.
-@node sparse
-@subsection Archiving Sparse Files
-@cindex Sparse Files
-@UNREVISED
+@FIXME{Describe how @acronym{POSIX} archives are extracted by non
+POSIX-aware tars.}
-@table @option
-@opindex sparse
-@item -S
-@itemx --sparse
-Handle sparse files efficiently.
-@end table
+@node Other Tars
+@subsection How to Extract GNU-Specific Data Using Other @command{tar} Implementations
-This option causes all files to be put in the archive to be tested for
-sparseness, and handled specially if they are. The @option{--sparse}
-(@option{-S}) 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 previous sections you became acquainted with various quirks
+necessary to make your archives portable. Sometimes you may need to
+extract archives containing GNU-specific members using some
+third-party @command{tar} implementation or an older version of
+@GNUTAR{}. Of course your best bet is to have @GNUTAR{} installed,
+but if it is for some reason impossible, this section will explain
+how to cope without it.
-In later versions, this option may be removed, and the testing and
-treatment of sparse files may be done automatically with any special
-@acronym{GNU} options. For now, it is an option needing to be specified on
-the command line with the creation or updating of an archive.
+When we speak about @dfn{GNU-specific} members we mean two classes of
+them: members split between the volumes of a multi-volume archive and
+sparse members. You will be able to always recover such members if
+the archive is in PAX format. In addition split members can be
+recovered from archives in old GNU format. The following subsections
+describe the required procedures in detail.
-Files in the file system 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, @command{tar}
-could create an archive longer than the original. To have @command{tar}
-attempt to recognize the holes in a file, use @option{--sparse} (@option{-S}). When
-you use this option, then, for any file using less disk space than
-would be expected from its length, @command{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
-@option{--sparse} is not needed on extraction) any such
-files have holes created wherever the continuous stretches of zeros
-were found. Thus, if you use @option{--sparse}, @command{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 @option{--sparse} option in conjunction with the @option{--create}
-(@option{-c}) operation, @command{tar} tests all files for sparseness
-while archiving. If @command{tar} finds a file to be sparse, it uses a
-sparse representation of the file in the archive. @xref{create}, for
-more information about creating archives.
-
-@option{--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.
+@menu
+* Split Recovery:: Members Split Between Volumes
+* Sparse Recovery:: Sparse Members
+@end menu
-@quotation
-@strong{Please Note:} Always use @option{--sparse} when performing file
-system backups, to avoid archiving the expanded forms of files stored
-sparsely in the system.
+@node Split Recovery
+@subsubsection Extracting Members Split Between Volumes
-Even if your system has no sparse files currently, some may be
-created in the future. If you use @option{--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
+@cindex Mutli-volume archives, extracting using non-GNU tars
+If a member is split between several volumes of an old GNU format archive
+most third party @command{tar} implementation will fail to extract
+it. To extract it, use @command{tarcat} program (@pxref{Tarcat}).
+This program is available from
+@uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tarcat.html, @GNUTAR{}
+home page}. It concatenates several archive volumes into a single
+valid archive. For example, if you have three volumes named from
+@file{vol-1.tar} to @file{vol-3.tar}, you can do the following to
+extract them using a third-party @command{tar}:
-@command{tar} ignores the @option{--sparse} option when reading an archive.
+@smallexample
+$ @kbd{tarcat vol-1.tar vol-2.tar vol-3.tar | tar xf -}
+@end smallexample
-@table @option
-@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
+@cindex Mutli-volume archives in PAX format, extracting using non-GNU tars
+You could use this approach for most (although not all) PAX
+format archives as well. However, extracting split members from a PAX
+archive is a much easier task, because PAX volumes are constructed in
+such a way that each part of a split member is extracted to a
+different file by @command{tar} implementations that are not aware of
+GNU extensions. More specifically, the very first part retains its
+original name, and all subsequent parts are named using the pattern:
-However, users should be well aware that at archive creation time,
-@GNUTAR{} 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 Sparcstation
-ELC, with full CPU utilization.)
-
-This reading is required in all cases and is not related to the fact
-the @option{--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 @option{--sparse} is selected while creating
-an archive, the current @command{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.}.
+@smallexample
+%d/GNUFileParts.%p/%f.%n
+@end smallexample
-Programs like @command{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.
-@GNUTAR{} 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:
+@noindent
+where symbols preceeded by @samp{%} are @dfn{macro characters} that
+have the following meaning:
-@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).
+@multitable @columnfractions .25 .55
+@headitem Meta-character @tab Replaced By
+@item %d @tab The directory name of the file, equivalent to the
+result of the @command{dirname} utility on its full name.
+@item %f @tab The file name of the file, equivalent to the result
+of the @command{basename} utility on its full name.
+@item %p @tab The process @acronym{ID} of the @command{tar} process that
+created the archive.
+@item %n @tab Ordinal number of this particular part.
+@end multitable
-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
+For example, if the file @file{var/longfile} was split during archive
+creation between three volumes, and the creator @command{tar} process
+had process @acronym{ID} @samp{27962}, then the member names will be:
-@node Attributes
-@section Handling File Attributes
-@UNREVISED
+@smallexample
+var/longfile
+var/GNUFileParts.27962/longfile.1
+var/GNUFileParts.27962/longfile.2
+@end smallexample
-When @command{tar} reads files, it updates their access times. To
-avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
-reset the access time retroactively or avoid changing it in the first
-place.
+When you extract your archive using a third-party @command{tar}, these
+files will be created on your disk, and the only thing you will need
+to do to restore your file in its original form is concatenate them in
+the proper order, for example:
-Handling of file attributes
+@smallexample
+@group
+$ @kbd{cd var}
+$ @kbd{cat GNUFileParts.27962/longfile.1 \
+ GNUFileParts.27962/longfile.2 >> longfile}
+$ rm -f GNUFileParts.27962
+@end group
+@end smallexample
-@table @option
-@opindex atime-preserve
-@item --atime-preserve
-@itemx --atime-preserve=replace
-@itemx --atime-preserve=system
-Preserve the access times of files that are read. This works only for
-files that you own, unless you have superuser privileges.
+Notice, that if the @command{tar} implementation you use supports PAX
+format archives, it will probably emit warnings about unknown keywords
+during extraction. They will look like this:
-@option{--atime-preserve=replace} works on most systems, but it also
-restores the data modification time and updates the status change
-time. Hence it doesn't interact with incremental dumps nicely
-(@pxref{Backups}), and it can set access or data modification times
-incorrectly if other programs access the file while @command{tar} is
-running.
+@smallexample
+@group
+Tar file too small
+Unknown extended header keyword 'GNU.volume.filename' ignored.
+Unknown extended header keyword 'GNU.volume.size' ignored.
+Unknown extended header keyword 'GNU.volume.offset' ignored.
+@end group
+@end smallexample
-@option{--atime-preserve=system} avoids changing the access time in
-the first place, if the operating system supports this.
-Unfortunately, this may or may not work on any given operating system
-or file system. If @command{tar} knows for sure it won't work, it
-complains right away.
+@noindent
+You can safely ignore these warnings.
-Currently @option{--atime-preserve} with no operand defaults to
-@option{--atime-preserve=replace}, but this is intended to change to
-@option{--atime-preserve=system} when the latter is better-supported.
+If your @command{tar} implementation is not PAX-aware, you will get
+more warnings and more files generated on your disk, e.g.:
-@opindex touch
-@item -m
-@itemx --touch
-Do not extract data modification time.
+@smallexample
+@group
+$ @kbd{tar xf vol-1.tar}
+var/PaxHeaders.27962/longfile: Unknown file type 'x', extracted as
+normal file
+Unexpected EOF in archive
+$ @kbd{tar xf vol-2.tar}
+tmp/GlobalHead.27962.1: Unknown file type 'g', extracted as normal file
+GNUFileParts.27962/PaxHeaders.27962/sparsefile.1: Unknown file type
+'x', extracted as normal file
+@end group
+@end smallexample
-When this option is used, @command{tar} leaves the data modification times
-of the files it extracts as the times when the files were extracted,
-instead of setting it to the times recorded in the archive.
+Ignore these warnings. The @file{PaxHeaders.*} directories created
+will contain files with @dfn{extended header keywords} describing the
+extracted files. You can delete them, unless they describe sparse
+members. Read further to learn more about them.
-This option is meaningless with @option{--list} (@option{-t}).
+@node Sparse Recovery
+@subsubsection Extracting Sparse Members
-@opindex same-owner
-@item --same-owner
-Create extracted files with the same ownership they have in the
-archive.
+@cindex sparse files, extracting with non-GNU tars
+Any @command{tar} implementation will be able to extract sparse members from a
+PAX archive. However, the extracted files will be @dfn{condensed},
+i.e., any zero blocks will be removed from them. When we restore such
+a condensed file to its original form, by adding zero blocks (or
+@dfn{holes}) back to their original locations, we call this process
+@dfn{expanding} a compressed sparse file.
-This is the default behavior for the superuser,
-so this option is meaningful only for non-root users, when @command{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.
+@pindex xsparse
+To expand a file, you will need a simple auxiliary program called
+@command{xsparse}. It is available in source form from
+@uref{http://www.gnu.org/@/software/@/tar/@/utils/@/xsparse.html, @GNUTAR{}
+home page}.
-When writing an archive, @command{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 @option{--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.
+@cindex sparse files v.1.0, extracting with non-GNU tars
+Let's begin with archive members in @dfn{sparse format
+version 1.0}@footnote{@xref{PAX 1}.}, which are the easiest to expand.
+The condensed file will contain both file map and file data, so no
+additional data will be needed to restore it. If the original file
+name was @file{@var{dir}/@var{name}}, then the condensed file will be
+named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where
+@var{n} is a decimal number@footnote{technically speaking, @var{n} is a
+@dfn{process @acronym{ID}} of the @command{tar} process which created the
+archive (@pxref{PAX keywords}).}.
-@opindex no-same-owner
-@item --no-same-owner
-@itemx -o
-Do not attempt to restore ownership when extracting. This is the
-default behavior for ordinary users, so this option has an effect
-only for the superuser.
+To expand a version 1.0 file, run @command{xsparse} as follows:
-@opindex numeric-owner
-@item --numeric-owner
-The @option{--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.
+@smallexample
+$ @kbd{xsparse @file{cond-file}}
+@end smallexample
-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 file system(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.
+@noindent
+where @file{cond-file} is the name of the condensed file. The utility
+will deduce the name for the resulting expanded file using the
+following algorithm:
+
+@enumerate 1
+@item If @file{cond-file} does not contain any directories,
+@file{../cond-file} will be used;
+
+@item If @file{cond-file} has the form
+@file{@var{dir}/@var{t}/@var{name}}, where both @var{t} and @var{name}
+are simple names, with no @samp{/} characters in them, the output file
+name will be @file{@var{dir}/@var{name}}.
+
+@item Otherwise, if @file{cond-file} has the form
+@file{@var{dir}/@var{name}}, the output file name will be
+@file{@var{name}}.
+@end enumerate
-The numeric ids are @emph{always} saved into @command{tar} archives.
-The identifying names are added at create time when provided by the
-system, unless @option{--old-archive} (@option{-o}) 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.
+In the unlikely case when this algorithm does not suit your needs,
+you can explicitly specify output file name as a second argument to
+the command:
-When making a @command{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
-@command{tar} archive out of this directory, before cleaning
-everything out. Of course, we could add a lot of options to
-@GNUTAR{} for fine tuning permissions and ownership.
-This is not the good way, I think. @GNUTAR{} is
-already crowded with options and moreover, the approach just explained
-gives you a great deal of control already.
+@smallexample
+$ @kbd{xsparse @file{cond-file} @file{out-file}}
+@end smallexample
-@opindex same-permissions, short description
-@opindex preserve-permissions, short description
-@item -p
-@itemx --same-permissions
-@itemx --preserve-permissions
-Extract all protection information.
+It is often a good idea to run @command{xsparse} in @dfn{dry run} mode
+first. In this mode, the command does not actually expand the file,
+but verbosely lists all actions it would be taking to do so. The dry
+run mode is enabled by @option{-n} command line argument:
-This option causes @command{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 by default enabled when
-@command{tar} is executed by a superuser.
+@smallexample
+@group
+$ @kbd{xsparse -n /home/gray/GNUSparseFile.6058/sparsefile}
+Reading v.1.0 sparse map
+Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
+`/home/gray/sparsefile'
+Finished dry run
+@end group
+@end smallexample
+To actually expand the file, you would run:
-This option is meaningless with @option{--list} (@option{-t}).
+@smallexample
+$ @kbd{xsparse /home/gray/GNUSparseFile.6058/sparsefile}
+@end smallexample
-@opindex preserve
-@item --preserve
-Same as both @option{--same-permissions} and @option{--same-order}.
+@noindent
+The program behaves the same way all UNIX utilities do: it will keep
+quiet unless it has simething important to tell you (e.g. an error
+condition or something). If you wish it to produce verbose output,
+similar to that from the dry run mode, use @option{-v} option:
-The @option{--preserve} option has no equivalent short option name.
-It is equivalent to @option{--same-permissions} plus @option{--same-order}.
+@smallexample
+@group
+$ @kbd{xsparse -v /home/gray/GNUSparseFile.6058/sparsefile}
+Reading v.1.0 sparse map
+Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
+`/home/gray/sparsefile'
+Done
+@end group
+@end smallexample
-@FIXME{I do not see the purpose of such an option. (Neither I. FP.)}
+Additionally, if your @command{tar} implementation has extracted the
+@dfn{extended headers} for this file, you can instruct @command{xstar}
+to use them in order to verify the integrity of the expanded file.
+The option @option{-x} sets the name of the extended header file to
+use. Continuing our example:
-@end table
+@smallexample
+@group
+$ @kbd{xsparse -v -x /home/gray/PaxHeaders.6058/sparsefile \
+ /home/gray/GNUSparseFile.6058/sparsefile}
+Reading extended header file
+Found variable GNU.sparse.major = 1
+Found variable GNU.sparse.minor = 0
+Found variable GNU.sparse.name = sparsefile
+Found variable GNU.sparse.realsize = 217481216
+Reading v.1.0 sparse map
+Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
+`/home/gray/sparsefile'
+Done
+@end group
+@end smallexample
-@node Standard
-@section Basic Tar Format
-@UNREVISED
+@anchor{extracting sparse v.0.x}
+@cindex sparse files v.0.1, extracting with non-GNU tars
+@cindex sparse files v.0.0, extracting with non-GNU tars
+An @dfn{extended header} is a special @command{tar} archive header
+that precedes an archive member and contains a set of
+@dfn{variables}, describing the member properties that cannot be
+stored in the standard @code{ustar} header. While optional for
+expanding sparse version 1.0 members, the use of extended headers is
+mandatory when expanding sparse members in older sparse formats: v.0.0
+and v.0.1 (The sparse formats are described in detail in @ref{Sparse
+Formats}.) So, for these formats, the question is: how to obtain
+extended headers from the archive?
+
+If you use a @command{tar} implementation that does not support PAX
+format, extended headers for each member will be extracted as a
+separate file. If we represent the member name as
+@file{@var{dir}/@var{name}}, then the extended header file will be
+named @file{@var{dir}/@/PaxHeaders.@var{n}/@/@var{name}}, where
+@var{n} is an integer number.
+
+Things become more difficult if your @command{tar} implementation
+does support PAX headers, because in this case you will have to
+manually extract the headers. We recommend the following algorithm:
+
+@enumerate 1
+@item
+Consult the documentation of your @command{tar} implementation for an
+option that prints @dfn{block numbers} along with the archive
+listing (analogous to @GNUTAR{}'s @option{-R} option). For example,
+@command{star} has @option{-block-number}.
+
+@item
+Obtain verbose listing using the @samp{block number} option, and
+find block numbers of the sparse member in question and the member
+immediately following it. For example, running @command{star} on our
+archive we obtain:
-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 @command{tar} utility or Tar mode in
-@acronym{GNU} Emacs.
-
-Physically, an archive consists of a series of file entries terminated
-by an end-of-archive entry, which consists of two 512 blocks of 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 @command{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}.
-@FIXME-xref{To learn more about having more than one archive member with the
-same name, see -backup node, when it's written.}
-
-In addition to entries describing archive members, an archive may
-contain entries which @command{tar} itself uses to store information.
-@xref{label}, for an example of such an archive entry.
-
-A @command{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 are two 512-byte blocks
-filled with binary zeros as an end-of-file marker. A reasonable system
-should write such end-of-file marker at the end of an archive, but
-must not assume that such a block exists when reading an archive. In
-particular @GNUTAR{} always issues a warning if it does not encounter it.
-
-The blocks may be @dfn{blocked} for physical I/O operations.
-Each record of @var{n} blocks (where @var{n} is set by the
-@option{--blocking-factor=@var{512-size}} (@option{-b @var{512-size}}) option to @command{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 @GNUTAR{}
-distribution, this is part of file @file{src/tar.h}:
-
-@smallexample
-@include header.texi
-@end smallexample
-
-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 @command{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 fields
-are zero-filled octal numbers in ASCII. Each numeric field of width
-@var{w} contains @var{w} minus 1 digits, and a 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 @option{--incremental} (@option{-G}) option.}
-
-The @code{mtime} field is the data 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's contents were 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, @command{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 and
-status change times.
-
-The @code{offset} is used by the @option{--multi-volume} (@option{-M}) 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 @command{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 @command{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
-allotted 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.
+@smallexample
+@group
+$ @kbd{star -t -v -block-number -f arc.tar}
+@dots{}
+star: Unknown extended header keyword 'GNU.sparse.size' ignored.
+star: Unknown extended header keyword 'GNU.sparse.numblocks' ignored.
+star: Unknown extended header keyword 'GNU.sparse.name' ignored.
+star: Unknown extended header keyword 'GNU.sparse.map' ignored.
+block 56: 425984 -rw-r--r-- gray/users Jun 25 14:46 2006 GNUSparseFile.28124/sparsefile
+block 897: 65391 -rw-r--r-- gray/users Jun 24 20:06 2006 README
+@dots{}
+@end group
+@end smallexample
-@table @asis
+@noindent
+(as usual, ignore the warnings about unknown keywords.)
-@item @code{REGTYPE}
-@itemx @code{AREGTYPE}
-These flags represent a regular file. In order to be compatible
-with older versions of @command{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, @command{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 @acronym{GNU} modified format, as described below.
+@item
+Let @var{size} be the size of the sparse member, @var{Bs} be its block number
+and @var{Bn} be the block number of the next member.
+Compute:
-@end table
+@smallexample
+@var{N} = @var{Bs} - @var{Bn} - @var{size}/512 - 2
+@end smallexample
-Other values are reserved for specification in future revisions of
-the P1003 standard, and should not be used by any @command{tar} program.
+@noindent
+This number gives the size of the extended header part in tar @dfn{blocks}.
+In our example, this formula gives: @code{897 - 56 - 425984 / 512 - 2
+= 7}.
-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.
+@item
+Use @command{dd} to extract the headers:
-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}.
+@smallexample
+@kbd{dd if=@var{archive} of=@var{hname} bs=512 skip=@var{Bs} count=@var{N}}
+@end smallexample
-@node Extensions
-@section @acronym{GNU} Extensions to the Archive Format
-@UNREVISED
+@noindent
+where @var{archive} is the archive name, @var{hname} is a name of the
+file to store the extended header in, @var{Bs} and @var{N} are
+computed in previous steps.
-The @acronym{GNU} format uses additional file types to describe new types of
-files in an archive. These are listed below.
+In our example, this command will be
-@table @code
-@item GNUTYPE_DUMPDIR
-@itemx 'D'
-This represents a directory and a list of files created by the
-@option{--incremental} (@option{-G}) 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 @option{--multi-volume} (@option{-M}) 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 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}}) option when the archive was created. The @code{name}
-field contains the @code{name} given after the @option{--label=@var{archive-label}} (@option{-V @var{archive-label}}) option.
-The @code{size} field is zero. Only the first file in each volume
-of an archive should have this type.
+@smallexample
+$ @kbd{dd if=arc.tar of=xhdr bs=512 skip=56 count=7}
+@end smallexample
+@end enumerate
-@end table
+Finally, you can expand the condensed file, using the obtained header:
-You may have trouble reading a @acronym{GNU} format archive on a
-non-@acronym{GNU} system if the options @option{--incremental} (@option{-G}),
-@option{--multi-volume} (@option{-M}), @option{--sparse} (@option{-S}), or @option{--label=@var{archive-label}} (@option{-V @var{archive-label}}) were
-used when writing the archive. In general, if @command{tar} does not
-use the @acronym{GNU}-added fields of the header, other versions of
-@command{tar} should be able to read the archive. Otherwise, the
-@command{tar} program will give an error, the most likely one being a
-checksum error.
+@smallexample
+@group
+$ @kbd{xsparse -v -x xhdr GNUSparseFile.6058/sparsefile}
+Reading extended header file
+Found variable GNU.sparse.size = 217481216
+Found variable GNU.sparse.numblocks = 208
+Found variable GNU.sparse.name = sparsefile
+Found variable GNU.sparse.map = 0,2048,1050624,2048,@dots{}
+Expanding file `GNUSparseFile.28124/sparsefile' to `sparsefile'
+Done
+@end group
+@end smallexample
@node cpio
@section Comparison of @command{tar} and @command{cpio}
@FIXME{Reorganize the following material}
The @command{cpio} archive formats, like @command{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. @acronym{GNU} @command{cpio} can read and write archives
-with arbitrary pathname lengths, but other @command{cpio} implementations
+file name lengths. The binary and old @acronym{ASCII} formats have a maximum file
+length of 256, and the new @acronym{ASCII} and @acronym{CRC ASCII} formats have a max
+file length of 1024. @acronym{GNU} @command{cpio} can read and write archives
+with arbitrary file name lengths, but other @command{cpio} implementations
may crash unexplainedly trying to read them.
-@command{tar} handles symbolic links in the form in which it comes in BSD;
+@command{tar} handles symbolic links in the form in which it comes in @acronym{BSD};
@command{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 @command{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 @command{cpio} that Berkeley picked up from AT&T and put
-into a later BSD release---I think I gave them my changes).
+into a later @acronym{BSD} release---I think I gave them my changes).
(SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio}
can handle @command{tar} format input, and write it on output, and it
@command{cpio} handles special files; traditional @command{tar} doesn't.
-@command{tar} comes with V7, System III, System V, and BSD source;
-@command{cpio} comes only with System III, System V, and later BSD
+@command{tar} comes with V7, System III, System V, and @acronym{BSD} source;
+@command{cpio} comes only with System III, System V, and later @acronym{BSD}
(4.3-tahoe and later).
@command{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);
-@command{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
+file systems that support 32-bit inumbers (e.g., the @acronym{BSD} file system);
+@command{cpio}s way requires you to play some games (in its ``binary''
+format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format,
+they're 18 bits---it would have to play games with the "file system @acronym{ID}"
+field of the header to make sure that the file system @acronym{ID}/i-number pairs
of different files were always different), and I don't know which
@command{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
@file{<sys/mtio.h>}.
@table @option
-@opindex force-local, short description
+@xopindex{force-local, short description}
@item --force-local
Archive file is local even if it contains a colon.
@item -[0-7][lmh]
Specify drive and density.
-@opindex multi-volume, short description
+@xopindex{multi-volume, short description}
@item -M
@itemx --multi-volume
Create/list/extract multi-volume archive.
that may be larger than will fit on the medium used to hold it.
@xref{Multi-Volume Archives}.
-@opindex tape-length, short description
+@xopindex{tape-length, short description}
@item -L @var{num}
@itemx --tape-length=@var{num}
Change tape after writing @var{num} x 1024 bytes.
detect end of physical tapes. By being slightly conservative on the
maximum tape length, you might avoid the problem entirely.
-@opindex info-script, short description
-@opindex new-volume-script, short description
+@xopindex{info-script, short description}
+@xopindex{new-volume-script, short description}
@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
@option{--multi-volume} (@option{-M}). @xref{info-script}, for a detailed
-description of this option.
+description of this option.
@end table
@node Remote Tape Server
This means that the @option{--append}, @option{--concatenate}, and
@option{--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.
+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 @command{tar} will work on them
once @command{tar} is modified to do so.
@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.
+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
@opindex blocking-factor
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
+@dfn{records}. The number of blocks in a record (i.e., the size of a
record in units of 512 bytes) is called the @dfn{blocking factor}.
The @option{--blocking-factor=@var{512-size}} (@option{-b
@var{512-size}}) option specifies the blocking factor of an archive.
The default blocking factor is typically 20 (i.e., 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.
+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
blocking factor (particularly if you're not sure what the blocking factor
is), you can usually use the @option{--read-full-records} (@option{-B}) option while
specifying a blocking factor larger then the blocking factor of the archive
-(ie. @samp{tar --extract --read-full-records --blocking-factor=300}.
+(i.e., @samp{tar --extract --read-full-records --blocking-factor=300}.
@xref{list}, for more information on the @option{--list} (@option{-t})
operation. @xref{Reading}, for a more detailed explanation of that option.
@command{tar} should rather drain the pipe out before exiting itself.
@end itemize
-@opindex ignore-zeros, short description
+@xopindex{ignore-zeros, short description}
@item -i
@itemx --ignore-zeros
Ignore blocks of zeros in archive (means EOF).
archive file, which may sometimes avoid problems when multiple files
are stored on a single physical tape.
-@opindex read-full-records, short description
+@xopindex{read-full-records, short description}
@item -B
@itemx --read-full-records
-Reblock as we read (for reading 4.2BSD pipes).
+Reblock as we read (for reading 4.2@acronym{BSD} pipes).
If @option{--read-full-records} is used, @command{tar}
will not panic if an attempt to read a record from the archive does
-not return a full record. Instead, @command{tar} will keep reading
-until it has obtained a full
+not return a full record. Instead, @command{tar} will keep reading
+until it has obtained a full
record.
This option is turned on by default when @command{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
+because on @acronym{BSD} Unix systems, a read of a pipe will return however
much happens to be in the pipe, even if it is less than @command{tar}
requested. If this option was not used, @command{tar} would fail as
soon as it read an incomplete record from the pipe.
@FIXME{Is there a better way to frob the spacing on the list?}
If you don't specify a @var{tapename}, @command{mt} uses the environment
-variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} uses the device
-@file{/dev/rmt12}.
+variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use
+the default device specified in your @file{sys/mtio.h} file
+(@code{DEFTAPE} variable). If this is not defined, the program will
+display a descriptive error message and exit with code 1.
@command{mt} returns a 0 exit status when the operation(s) were
successful, 1 if the command was unrecognized, and 2 if an operation
@node Using Multiple Tapes
@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
@command{tar} commands, but this can be inconvenient, particularly if you
are using options like @option{--exclude=@var{pattern}} or dumping entire file systems.
-Therefore, @command{tar} supports multiple tapes automatically.
+Therefore, @command{tar} provides a special mode for creating
+multi-volume archives.
+
+@dfn{Multi-volume} archive is a single @command{tar} archive, stored
+on several media volumes of fixed size. Although in this section we will
+often call @samp{volume} a @dfn{tape}, there is absolutely no
+requirement for multi-volume archives to be stored on tapes. Instead,
+they can use whatever media type the user finds convenient, they can
+even be located on files.
+
+When creating a multi-volume archive, @GNUTAR{} continues to fill
+current volume until it runs out of space, then it switches to
+next volume (usually the operator is queried to replace the tape on
+this point), and continues working on the new volume. This operation
+continues until all requested files are dumped. If @GNUTAR{} detects
+end of media while dumping a file, such a file is archived in split
+form. Some very big files can even be split across several volumes.
+
+Each volume is itself a valid @GNUTAR{} archive, so it can be read
+without any special options. Consequently any file member residing
+entirely on one volume can be extracted or otherwise operated upon
+without needing the other volume. Sure enough, to extract a split
+member you would need all volumes its parts reside on.
+
+Multi-volume archives suffer from several limitations. In particular,
+they cannot be compressed.
+
+@GNUTAR{} is able to create multi-volume archives of two formats
+(@pxref{Formats}): @samp{GNU} and @samp{POSIX}.
+
+@menu
+* Multi-Volume Archives:: Archives Longer than One Tape or Disk
+* Tape Files:: Tape Files
+* Tarcat:: Concatenate Volumes into a Single Archive
+
+@end menu
+
+@node Multi-Volume Archives
+@subsection Archives Longer than One Tape or Disk
+@cindex Multi-volume archives
+
+@opindex multi-volume
+To create an archive that is larger than will fit on a single unit of
+the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with
+the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
+archive can be manipulated like any other archive (provided the
+@option{--multi-volume} option is specified), but is stored on more
+than one tape or disk.
+
+When you specify @option{--multi-volume}, @command{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.
+
+@table @option
+@item --multi-volume
+@itemx -M
+Creates a multi-volume archive, when used in conjunction with
+@option{--create} (@option{-c}). To perform any other operation on a multi-volume
+archive, specify @option{--multi-volume} in conjunction with that
+operation.
+For example:
+
+@smallexample
+$ @kbd{tar --create --multi-volume --file=/dev/tape @var{files}}
+@end smallexample
+@end table
+
+The method @command{tar} uses to detect end of tape is not perfect, and
+fails on some operating systems or on some devices. If @command{tar}
+cannot detect the end of the tape itself, you can use
+@option{--tape-length} option to inform it about the capacity of the
+tape:
+
+@anchor{tape-length}
+@table @option
+@opindex tape-length
+@item --tape-length=@var{size}
+@itemx -L @var{size}
+Set maximum length of a volume. The @var{size} argument should then
+be the usable size of the tape in units of 1024 bytes. This option
+selects @option{--multi-volume} automatically. For example:
-Use @option{--multi-volume} (@option{-M}) on the command line, and
-then @command{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 @command{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
-@option{--multi-volume}, and then put in the second tape when
-prompted, so @command{tar} can restore both halves of the file.)
+@smallexample
+$ @kbd{tar --create --tape-length=41943040 --file=/dev/tape @var{files}}
+@end smallexample
+@end table
+
+@anchor{change volume prompt}
+When @GNUTAR{} comes to the end of a storage media, it asks you to
+change the volume. The built-in prompt for POSIX locale
+is@footnote{If you run @GNUTAR{} under a different locale, the
+translation to the locale's language will be used.}:
-@GNUTAR{} multi-volume archives do not use a truly portable format.
-You need @GNUTAR{} at both ends to process them properly.
+@smallexample
+Prepare volume #@var{n} for `@var{archive}' and hit return:
+@end smallexample
+
+@noindent
+where @var{n} is the ordinal number of the volume to be created and
+@var{archive} is archive file or device name.
When prompting for a new tape, @command{tar} accepts any of the following
responses:
Request @command{tar} to explain possible responses
@item q
Request @command{tar} to exit immediately.
-@item n @var{file name}
-Request @command{tar} to write the next volume on the file @var{file name}.
+@item n @var{file-name}
+Request @command{tar} to write the next volume on the file @var{file-name}.
@item !
Request @command{tar} to run a subshell. This option can be disabled
-by giving @option{--restrict} command line option to @command{tar}.
+by giving @option{--restrict} command line option to
+@command{tar}@footnote{@xref{--restrict}, for more information about
+this option}.
@item y
Request @command{tar} to begin writing the next volume.
@end table
(You should only type @samp{y} after you have changed the tape;
otherwise @command{tar} will write over the volume it just finished.)
+@cindex Volume number file
+@cindex volno file
+@anchor{volno-file}
+@opindex volno-file
+The volume number used by @command{tar} in its tape-changing prompt
+can be changed; if you give the
+@option{--volno-file=@var{file-of-number}} option, then
+@var{file-of-number} should be an non-existing 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
+@command{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 @ref{label}, it @emph{only} affects
+the number used in the prompt.)
+
@cindex End-of-archive info script
@cindex Info script
@anchor{info-script}
@opindex info-script
@opindex new-volume-script
-If you want more elaborate behavior than this, give @command{tar} the
-@option{--info-script=@var{script-name}}
-(@option{--new-volume-script=@var{script-name}}, @option{-F
-@var{script-name}}) option. The file @var{script-name} is expected to
-be a program (or shell script) to be run instead of the normal
-prompting procedure. It is executed without any command line
-arguments. Additional data is passed to it via the following
-environment variables:
+If you want more elaborate behavior than this, you can write a special
+@dfn{new volume script}, that will be responsible for changing the
+volume, and instruct @command{tar} to use it instead of its normal
+prompting procedure:
+
+@table @option
+@item --info-script=@var{script-name}
+@itemx --new-volume-script=@var{script-name}
+@itemx -F @var{script-name}
+Specify the full name of the volume script to use. The script can be
+used to eject cassettes, or to broadcast messages such as
+@samp{Someone please come change my tape} when performing unattended
+backups.
+@end table
+
+The @var{script-name} is executed without any command line
+arguments. It inherits @command{tar}'s shell environment.
+Additional data is passed to it via the following
+environment variables:
@table @env
@vrindex TAR_VERSION, info script environment variable
@item TAR_VERSION
@GNUTAR{} version number.
-@vrindex TAR_ARCHIVE, info script environment variable
+@vrindex TAR_ARCHIVE, info script environment variable
@item TAR_ARCHIVE
The name of the archive @command{tar} is processing.
+@vrindex TAR_BLOCKING_FACTOR, info script environment variable
+@item TAR_BLOCKING_FACTOR
+Current blocking factor (@pxref{Blocking}.
+
@vrindex TAR_VOLUME, info script environment variable
@item TAR_VOLUME
Ordinal number of the volume @command{tar} is about to start.
@vrindex TAR_SUBCOMMAND, info script environment variable
@item TAR_SUBCOMMAND
-Short option describing the operation @command{tar} is executed.
+A short option describing the operation @command{tar} is executing
@xref{Operations}, for a complete list of subcommand options.
@vrindex TAR_FORMAT, info script environment variable
@item TAR_FORMAT
Format of the archive being processed. @xref{Formats}, for a complete
-list of archive format names.
+list of archive format names.
+
+@vrindex TAR_FD, info script environment variable
+@item TAR_FD
+File descriptor which can be used to communicate the new volume
+name to @command{tar}.
@end table
-The info script can instruct @command{tar} to use new archive name,
-by writing in to file descriptor 3 (see below for an
-example).
+The volume script can instruct @command{tar} to use new archive name,
+by writing in to file descriptor @env{$TAR_FD} (see below for an example).
If the info script fails, @command{tar} exits; otherwise, it begins
-writing the next volume.
-
-The method @command{tar} uses to detect end of tape is not perfect, and
-fails on some operating systems or on some devices. You can use the
-@option{--tape-length=@var{size}} (@option{-L @var{size}}) option if
-@command{tar} can't detect the end of the tape itself. This option
-selects @option{--multi-volume} (@option{-M}) automatically. The
-@var{size} argument should then be the usable size of the tape in
-units of 1024 bytes. But for many devices, and floppy disks in
-particular, this option is never required for real, as far as we know.
-
-@cindex Volume number file
-@cindex volno file
-@anchor{volno-file}
-@opindex volno-file
-The volume number used by @command{tar} in its tape-change prompt
-can be changed; if you give the
-@option{--volno-file=@var{file-of-number}} 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
-@command{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 @ref{label}, it @emph{only} affects
-the number used in the prompt.)
+writing the next volume.
If you want @command{tar} to cycle through a series of files or tape
drives, there are three approaches to choose from. First of all, you
-can give @command{tar} multiple @option{--file} options. In this case
+can give @command{tar} multiple @option{--file} options. In this case
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 @command{tar} prompt for a tape change (or run
-the info script). Secondly, you can use the @samp{n} response to the
-tape-change prompt, and, finally, you can use an info script, that
-writes new archive name to file descriptor. The following example
-illustrates this approach:
+the info script). For example, suppose someone has two tape drives on
+a system named @file{/dev/tape0} and @file{/dev/tape1}. For having
+@GNUTAR{} 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
+
+The second method is to use the @samp{n} response to the tape-change
+prompt.
+
+Finally, the most flexible approach is to use a volume script, that
+writes new archive name to the file descriptor @env{$TAR_FD}. For example, the
+following volume script will create a series of archive files, named
+@file{@var{archive}-@var{vol}}, where @var{archive} is the name of the
+archive being created (as given by @option{--file} option) and
+@var{vol} is the ordinal number of the archive being created:
@smallexample
@group
case $TAR_SUBCOMMAND in
-c) ;;
-d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1
- ;;
+ ;;
*) exit 1
esac
-echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&3
+echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&$TAR_FD
@end group
@end smallexample
-Each volume of a multi-volume archive is an independent @command{tar}
-archive, complete in itself. For example, you can list or extract any
-volume alone; just don't specify @option{--multi-volume}
-(@option{-M}). 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 @option{--extract --multi-volume}
-(@option{-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 @GNUTAR{}
-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:
+The same script can be used while listing, comparing or extracting
+from the created archive. For example:
@smallexample
-$ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}}
-$ @kbd{tar cMff /dev/tape0 /dev/tape1 @var{files}}
+@group
+# @r{Create a multi-volume archive:}
+$ @kbd{tar -c -L1024 -f archive.tar -F new-volume .}
+# @r{Extract from the created archive:}
+$ @kbd{tar -x -f archive.tar -F new-volume .}
+@end group
@end smallexample
-@menu
-* Multi-Volume Archives:: Archives Longer than One Tape or Disk
-* Tape Files:: Tape Files
-* Tarcat:: Concatenate Volumes into a Single Archive
-
-@end menu
-
-@node Multi-Volume Archives
-@subsection Archives Longer than One Tape or Disk
-@cindex Multi-volume archives
-@UNREVISED
-
-@opindex multi-volume
-To create an archive that is larger than will fit on a single unit of
-the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with
-the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
-archive can be manipulated like any other archive (provided the
-@option{--multi-volume} option is specified), but is stored on more
-than one tape or disk.
-
-When you specify @option{--multi-volume}, @command{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.
+@noindent
+Notice, that the first command had to use @option{-L} option, since
+otherwise @GNUTAR{} will end up writing everything to file
+@file{archive.tar}.
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
that volume), use @option{--extract}, again without
@option{--multi-volume}.
-If an archive member is split across volumes (ie. its entry begins on
+If an archive member is split across volumes (i.e., its entry begins on
one volume of the media and ends on another), you need to specify
@option{--multi-volume} to extract it successfully. In this case, you
should load the volume where the archive member starts, and use
volumes as it needs them. @xref{extracting archives}, for more
information about extracting archives.
-@option{--info-script=@var{script-name}}
-(@option{--new-volume-script=@var{script-name}}, @option{-F
-@var{script-name}}) (@pxref{info-script}) is like
-@option{--multi-volume} (@option{-M}), except that @command{tar} does
-not prompt you directly to change media volumes when a volume is
-full---instead, @command{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, @command{tar} will assume that the media
-has been changed.
-
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
-@option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
-(@pxref{label}) when it was created, @command{tar} will not
-automatically label volumes which are added later. To label
-subsequent volumes, specify @option{--label=@var{archive-label}} again
-in conjunction with the @option{--append}, @option{--update} or
-@option{--concatenate} operation.
-
-@cindex Labeling multi-volume archives
-@FIXME{example}
-
-@FIXME{There should be a sample program here, including an exit
-before end. Is the exit status even checked in tar? :-(}
-
-@table @option
-@item --multi-volume
-@itemx -M
-Creates a multi-volume archive, when used in conjunction with
-@option{--create} (@option{-c}). To perform any other operation on a multi-volume
-archive, specify @option{--multi-volume} in conjunction with that
-operation.
-
-@item --info-script=@var{program-file}
-@itemx --new-volume-script=@var{program-file}
-@itemx -F @var{program-file}
-Creates a multi-volume archive via a script. Used in conjunction with
-@option{--create} (@option{-c}). @xref{info-script}, dor a detailed discussion.
-@end table
+@option{--label=@var{archive-label}} (@pxref{label}) when it was
+created, @command{tar} will not automatically label volumes which are
+added later. To label subsequent volumes, specify
+@option{--label=@var{archive-label}} again in conjunction with the
+@option{--append}, @option{--update} or @option{--concatenate} operation.
-Beware that there is @emph{no} real standard about the proper way, for
-a @command{tar} archive, to span volume boundaries. If you have a
-multi-volume created by some vendor's @command{tar}, there is almost
-no chance you could read all the volumes with @GNUTAR{}.
-The converse is also true: you may not expect
-multi-volume archives created by @GNUTAR{} to be
-fully recovered by vendor's @command{tar}. Since there is little
-chance that, in mixed system configurations, some vendor's
-@command{tar} will work on another vendor's machine, and there is a
-great chance that @GNUTAR{} will work on most of
-them, your best bet is to install @GNUTAR{} on all
-machines between which you know exchange of files is possible.
+Notice that multi-volume support is a GNU extension and the archives
+created in this mode should be read only using @GNUTAR{}. If you
+absolutely have to process such archives using a third-party @command{tar}
+implementation, read @ref{Split Recovery}.
@node Tape Files
@subsection Tape Files
you give, where @var{nnn} is the number of the volume of the archive.
(If you use the @option{--label=@var{volume-label}}) option when
reading an archive, it checks to make sure the label on the tape
-matches the one you give. @xref{label}.
+matches the one you give. @xref{label}.
When @command{tar} writes an archive to tape, it creates a single
tape file. If multiple archives are written to the same tape, one
@section Including a Label in the Archive
@cindex Labeling an archive
@cindex Labels on the archive media
+@cindex Labeling multi-volume archives
@UNREVISED
@opindex label
contains the name of the archive---in the archive itself. Use the
@option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
option in conjunction with the @option{--create} operation to include
-a label entry in the archive as it is being created.
+a label entry in the archive as it is being created.
@table @option
@item --label=@var{archive-label}
@cindex Listing volume label
The volume label will be displayed by @option{--list} along with
the file contents. If verbose display is requested, it will also be
-explicitely marked as in the example below:
+explicitly marked as in the example below:
@smallexample
@group
the archive label matches the one specified and will refuse to proceed
if it does not. Use this as a safety precaution to avoid accidentally
overwriting existing archives. For example, if you wish to add files
-to @file{archive}, presumably labelled with string @samp{My volume},
+to @file{archive}, presumably labeled with string @samp{My volume},
you will get:
@smallexample
@noindent
in case its label does not match. This will work even if
-@file{archive} is not labelled at all.
+@file{archive} is not labeled at all.
Similarly, @command{tar} will refuse to list or extract the
archive if its label doesn't match the @var{archive-label}
operation, or can compare a previously written archive, to insure that
it is up to date.
-@opindex verify, using with @option{--create}
-@opindex create, using with @option{--verify}
+@xopindex{verify, using with @option{--create}}
+@xopindex{create, using with @option{--verify}}
To check for discrepancies in an archive immediately after it is
written, use the @option{--verify} (@option{-W}) option in conjunction with
the @option{--create} operation. When this option is
One can explicitly compare an already made archive with the file
system by using the @option{--compare} (@option{--diff}, @option{-d})
option, instead of using the more automatic @option{--verify} option.
-@xref{compare}.
+@xref{compare}.
Note that these two options have a slightly different intent. The
@option{--compare} option checks how identical are the logical contents of some
archive with what is on your disks, while the @option{--verify} option is
really for checking if the physical contents agree and if the recording
-media itself is of dependable quality. So, for the @option{--verify}
+media itself is of dependable quality. So, for the @option{--verify}
operation, @command{tar} tries to defeat all in-memory cache pertaining to
the archive, while it lets the speed optimization undisturbed for the
@option{--compare} option. If you nevertheless use @option{--compare} for
conjunction with the @option{--multi-volume} (@option{-M}) option or
the @option{--append} (@option{-r}), @option{--update} (@option{-u})
and @option{--delete} operations. @xref{Operations}, for more
-information on these operations.
+information on these operations.
Also, since @command{tar} normally strips leading @samp{/} from file
names (@pxref{absolute}), a command like @samp{tar --verify -cf
@GNUTAR{} documentation page}.
@table @asis
+@item Use of globbing patterns when listing and extracting.
+
+Previous versions of GNU tar assumed shell-style globbing when
+extracting from or listing an archive. For example:
+
+@smallexample
+$ @kbd{tar xf foo.tar '*.c'}
+@end smallexample
+
+would extract all files whose names end in @samp{.c}. This behavior
+was not documented and was incompatible with traditional tar
+implementations. Therefore, starting from version 1.15.91, GNU tar
+no longer uses globbing by default. For example, the above invocation
+is now interpreted as a request to extract from the archive the file
+named @file{*.c}.
+
+To facilitate transition to the new behavior for those users who got
+used to the previous incorrect one, @command{tar} will print a warning
+if it finds out that a requested member was not found in the archive
+and its name looks like a globbing pattern. For example:
+
+@smallexample
+$ @kbd{tar xf foo.tar '*.c'}
+tar: Pattern matching characters used in file names. Please,
+tar: use --wildcards to enable pattern matching, or --no-wildcards to
+tar: suppress this warning.
+tar: *.c: Not found in archive
+tar: Error exit delayed from previous errors
+@end smallexample
+
+To treat member names as globbing patterns, use --wildcards option.
+If you want to tar to mimic the behavior of versions prior to 1.15.91,
+add this option to your @env{TAR_OPTIONS} variable.
+
+@xref{wildcards}, for the detailed discussion of the use of globbing
+patterns by @GNUTAR{}.
+
@item Use of short option @option{-o}.
Earlier versions of @GNUTAR{} understood @option{-o} command line
distribution tarballs. @xref{Formats,v7}, for the detailed discussion
of this issue and its implications.
+@FIXME{Change the first argument to tar-formats when the new Automake is
+out. The proposition to add @anchor{} to the appropriate place of its
+docs was accepted by Automake people --Sergey 2006-05-25}.
+@xref{Options, tar-v7, Changing Automake's Behavior,
+automake, GNU Automake}, for a description on how to use various
+archive formats with @command{automake}.
+
Future versions of @GNUTAR{} will understand @option{-o} only as a
synonym for @option{--no-same-owner}.
@item Use of short option @option{-l}
Earlier versions of @GNUTAR{} understood @option{-l} option as a
-synonym for @option{--one-file-system}. Such usage is deprecated.
-For compatibility with other implementations future versions of
-@GNUTAR{} will understand this option as a synonym for
-@option{--check-links}.
+synonym for @option{--one-file-system}. Since such usage contradicted
+to UNIX98 specification and harmed compatibility with other
+implementation, it was declared deprecated in version 1.14. However,
+to facilitate transition to its new semantics, it was supported by
+versions 1.15 and 1.15.90. The present use of @option{-l} as a short
+variant of @option{--check-links} was introduced in version 1.15.91.
@item Use of options @option{--portability} and @option{--old-archive}
This option is deprecated. Please use @option{--format=posix} instead.
@end table
+@node Configuring Help Summary
+@appendix Configuring Help Summary
+
+Running @kbd{tar --help} displays the short @command{tar} option
+summary (@pxref{help}). This summary is organized by @dfn{groups} of
+semantically close options. The options within each group are printed
+in the following order: a short option, eventually followed by a list
+of corresponding long option names, followed by a short description of
+the option. For example, here is an excerpt from the actual @kbd{tar
+--help} output:
+
+@verbatim
+ Main operation mode:
+
+ -A, --catenate, --concatenate append tar files to an archive
+ -c, --create create a new archive
+ -d, --diff, --compare find differences between archive and
+ file system
+ --delete delete from the archive
+@end verbatim
+
+@vrindex ARGP_HELP_FMT, environment variable
+The exact visual representation of the help output is configurable via
+@env{ARGP_HELP_FMT} environment variable. The value of this variable
+is a comma-separated list of @dfn{format variable} assignments. There
+are two kinds of format variables. An @dfn{offset variable} keeps the
+offset of some part of help output text from the leftmost column on
+the screen. A @dfn{boolean} variable is a flag that toggles some
+output feature on or off. Depending on the type of the corresponding
+variable, there are two kinds of assignments:
+
+@table @asis
+@item Offset assignment
+
+The assignment to an offset variable has the following syntax:
+
+@smallexample
+@var{variable}=@var{value}
+@end smallexample
+
+@noindent
+where @var{variable} is the variable name, and @var{value} is a
+numeric value to be assigned to the variable.
+
+@item Boolean assignment
+
+To assign @code{true} value to a variable, simply put this variable name. To
+assign @code{false} value, prefix the variable name with @samp{no-}. For
+example:
+
+@smallexample
+@group
+# Assign @code{true} value:
+dup-args
+# Assign @code{false} value:
+no-dup-args
+@end group
+@end smallexample
+@end table
+
+Following variables are declared:
+
+@deftypevr {Help Output} boolean dup-args
+If true, arguments for an option are shown with both short and long
+options, even when a given option has both forms, for example:
+
+@smallexample
+ -f ARCHIVE, --file=ARCHIVE use archive file or device ARCHIVE
+@end smallexample
+
+If false, then if an option has both short and long forms, the
+argument is only shown with the long one, for example:
+
+@smallexample
+ -f, --file=ARCHIVE use archive file or device ARCHIVE
+@end smallexample
+
+@noindent
+and a message indicating that the argument is applicable to both
+forms is printed below the options. This message can be disabled
+using @code{dup-args-note} (see below).
+
+The default is false.
+@end deftypevr
+
+@deftypevr {Help Output} boolean dup-args-note
+If this variable is true, which is the default, the following notice
+is displayed at the end of the help output:
+
+@quotation
+Mandatory or optional arguments to long options are also mandatory or
+optional for any corresponding short options.
+@end quotation
+
+Setting @code{no-dup-args-note} inhibits this message. Normally, only one of
+variables @code{dup-args} or @code{dup-args-note} should be set.
+@end deftypevr
+
+@deftypevr {Help Output} offset short-opt-col
+Column in which short options start. Default is 2.
+
+@smallexample
+@group
+$ @kbd{tar --help|grep ARCHIVE}
+ -f, --file=ARCHIVE use archive file or device ARCHIVE
+$ @kbd{ARGP_HELP_FMT=short-opt-col=6 tar --help|grep ARCHIVE}
+ -f, --file=ARCHIVE use archive file or device ARCHIVE
+@end group
+@end smallexample
+@end deftypevr
+
+@deftypevr {Help Output} offset long-opt-col
+Column in which long options start. Default is 6. For example:
+
+@smallexample
+@group
+$ @kbd{tar --help|grep ARCHIVE}
+ -f, --file=ARCHIVE use archive file or device ARCHIVE
+$ @kbd{ARGP_HELP_FMT=long-opt-col=16 tar --help|grep ARCHIVE}
+ -f, --file=ARCHIVE use archive file or device ARCHIVE
+@end group
+@end smallexample
+@end deftypevr
+
+@deftypevr {Help Output} offset doc-opt-col
+Column in which @dfn{doc options} start. A doc option isn't actually
+an option, but rather an arbitrary piece of documentation that is
+displayed in much the same manner as the options. For example, in
+the description of @option{--format} option:
+
+@smallexample
+@group
+ -H, --format=FORMAT create archive of the given format.
+
+ FORMAT is one of the following:
+
+ gnu GNU tar 1.13.x format
+ oldgnu GNU format as per tar <= 1.12
+ pax POSIX 1003.1-2001 (pax) format
+ posix same as pax
+ ustar POSIX 1003.1-1988 (ustar) format
+ v7 old V7 tar format
+@end group
+@end smallexample
+
+@noindent
+the format names are doc options. Thus, if you set
+@kbd{ARGP_HELP_FMT=doc-opt-col=6} the above part of the help output
+will look as follows:
+
+@smallexample
+@group
+ -H, --format=FORMAT create archive of the given format.
+
+ FORMAT is one of the following:
+
+ gnu GNU tar 1.13.x format
+ oldgnu GNU format as per tar <= 1.12
+ pax POSIX 1003.1-2001 (pax) format
+ posix same as pax
+ ustar POSIX 1003.1-1988 (ustar) format
+ v7 old V7 tar format
+@end group
+@end smallexample
+@end deftypevr
+
+@deftypevr {Help Output} offset opt-doc-col
+Column in which option description starts. Default is 29.
+
+@smallexample
+@group
+$ @kbd{tar --help|grep ARCHIVE}
+ -f, --file=ARCHIVE use archive file or device ARCHIVE
+$ @kbd{ARGP_HELP_FMT=opt-doc-col=19 tar --help|grep ARCHIVE}
+ -f, --file=ARCHIVE use archive file or device ARCHIVE
+$ @kbd{ARGP_HELP_FMT=opt-doc-col=9 tar --help|grep ARCHIVE}
+ -f, --file=ARCHIVE
+ use archive file or device ARCHIVE
+@end group
+@end smallexample
+
+@noindent
+Notice, that the description starts on a separate line if
+@code{opt-doc-col} value is too small.
+@end deftypevr
+
+@deftypevr {Help Output} offset header-col
+Column in which @dfn{group headers} are printed. A group header is a
+descriptive text preceding an option group. For example, in the
+following text:
+
+@verbatim
+ Main operation mode:
+
+ -A, --catenate, --concatenate append tar files to
+ an archive
+ -c, --create create a new archive
+@end verbatim
+@noindent
+@samp{Main operation mode:} is the group header.
+
+The default value is 1.
+@end deftypevr
+
+@deftypevr {Help Output} offset usage-indent
+Indentation of wrapped usage lines. Affects @option{--usage}
+output. Default is 12.
+@end deftypevr
+
+@deftypevr {Help Output} offset rmargin
+Right margin of the text output. Used for wrapping.
+@end deftypevr
+
+@node Fixing Snapshot Files
+@appendix Fixing Snapshot Files
+@include tar-snapshot-edit.texi
+
+@node Tar Internals
+@appendix Tar Internals
+@include intern.texi
+
@node Genfile
@appendix Genfile
@include genfile.texi
-@node Snapshot Files
-@appendix Format of the Incremental Snapshot Files
-@include snapshot.texi
-
@node Free Software Needs Free Documentation
@appendix Free Software Needs Free Documentation
@include freemanuals.texi
@appendix Index of Command Line Options
This appendix contains an index of all @GNUTAR{} long command line
-options. The options are listed without the preceeding double-dash.
-
-@FIXME{@itemize
-@item Make sure @emph{all} options are indexed.
-@item Provide an index of short options
-@end itemize}
+options. The options are listed without the preceding double-dash.
+For a cross-reference of short command line options, @ref{Short Option Summary}.
@printindex op
@c Local variables:
@c texinfo-column-for-description: 32
@c End:
-
projects / chaz / tar / blobdiff