* 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.
+* Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al.
Controlling the Archive Format
@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
+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
$ @kbd{tar --list --verbose --file=collection.tar folk}
--rw-r--r-- myself user 62 1990-05-23 10:55 folk
+-rw-r--r-- myself/user 62 1990-05-23 10:55 folk
@end smallexample
@cindex listing member and file names
@command{tar} responds:
@smallexample
-drwxrwxrwx myself user 0 1990-05-31 21:49 practice/
--rw-r--r-- myself user 42 1990-05-21 13:29 practice/blues
--rw-r--r-- myself user 62 1990-05-23 10:55 practice/folk
--rw-r--r-- myself user 40 1990-05-21 13:30 practice/jazz
--rw-r--r-- myself user 10240 1990-05-31 21:49 practice/collection.tar
+drwxrwxrwx myself/user 0 1990-05-31 21:49 practice/
+-rw-r--r-- myself/user 42 1990-05-21 13:29 practice/blues
+-rw-r--r-- myself/user 62 1990-05-23 10:55 practice/folk
+-rw-r--r-- myself/user 40 1990-05-21 13:30 practice/jazz
+-rw-r--r-- myself/user 10240 1990-05-31 21:49 practice/collection.tar
@end smallexample
When you use a directory name as a file name argument, @command{tar} acts on
produces this:
@smallexample
--rw-r--r-- me user 28 1996-10-18 16:31 jazz
--rw-r--r-- me user 21 1996-09-23 16:44 blues
--rw-r--r-- me user 20 1996-09-23 16:44 folk
+-rw-r--r-- me/user 28 1996-10-18 16:31 jazz
+-rw-r--r-- me/user 21 1996-09-23 16:44 blues
+-rw-r--r-- me/user 20 1996-09-23 16:44 folk
@end smallexample
@node extracting files
@smallexample
$ @kbd{tar -xvvf music.tar practice/folk practice/jazz}
--rw-r--r-- me user 28 1996-10-18 16:31 practice/jazz
--rw-r--r-- me user 20 1996-09-23 16:44 practice/folk
+-rw-r--r-- me/user 28 1996-10-18 16:31 practice/jazz
+-rw-r--r-- me/user 20 1996-09-23 16:44 practice/folk
@end smallexample
@noindent
@item --dereference
@itemx -h
-When creating a @command{tar} archive, @command{tar} will archive the
-file that a symbolic link points to, rather than archiving the
-symlink. @xref{dereference}.
+When reading or writing a file to be archived, @command{tar} accesses
+the file that a symbolic link points to, rather than the symlink
+itself. @xref{dereference}.
@opsummary{directory}
@item --directory=@var{dir}
@cindex @samp{Ignoring unknown extended header keyword `%s'}, warning message
@item unknown-keyword
@samp{Ignoring unknown extended header keyword `%s'}
+@kwindex decompress-program
+@item decompress-program
+Controls verbose description of failures occurring when trying to run
+alternative decompressor programs (@pxref{alternative decompression
+programs}). This warning is disabled by default (unless
+@option{--verbose} is used). A common example of what you can get
+when using this warning is:
+
+@smallexample
+$ @kbd{tar --warning=decompress-program -x -f archive.Z}
+tar (child): cannot run compress: No such file or directory
+tar (child): trying gzip
+@end smallexample
+
+This means that @command{tar} first tried to decompress
+@file{archive.Z} using @command{compress}, and, when that
+failed, switched to @command{gzip}.
@end table
@subheading Keywords controlling incremental extraction:
@smallexample
$ @kbd{tar --list --file=collection.tar}
--rw-r--r-- me user 28 1996-10-18 16:31 jazz
--rw-r--r-- me user 21 1996-09-23 16:44 blues
--rw-r--r-- me user 20 1996-09-23 16:44 folk
--rw-r--r-- me user 20 1996-09-23 16:44 rock
+-rw-r--r-- me/user 28 1996-10-18 16:31 jazz
+-rw-r--r-- me/user 21 1996-09-23 16:44 blues
+-rw-r--r-- me/user 20 1996-09-23 16:44 folk
+-rw-r--r-- me/user 20 1996-09-23 16:44 rock
@end smallexample
@node multiple
@smallexample
$ @kbd{tar --list --verbose --file=collection.tar}
--rw-r--r-- me user 28 1996-10-18 16:31 jazz
--rw-r--r-- me user 21 1996-09-23 16:44 blues
--rw-r--r-- me user 20 1996-09-23 16:44 folk
--rw-r--r-- me user 20 1996-09-23 16:44 rock
--rw-r--r-- me user 58 1996-10-24 18:30 blues
+-rw-r--r-- me/user 28 1996-10-18 16:31 jazz
+-rw-r--r-- me/user 21 1996-09-23 16:44 blues
+-rw-r--r-- me/user 20 1996-09-23 16:44 folk
+-rw-r--r-- me/user 20 1996-09-23 16:44 rock
+-rw-r--r-- me/user 58 1996-10-24 18:30 blues
@end smallexample
@noindent
@smallexample
$ @kbd{tar --extract -vv --occurrence --file=collection.tar blues}
--rw-r--r-- me user 21 1996-09-23 16:44 blues
+-rw-r--r-- me/user 21 1996-09-23 16:44 blues
@end smallexample
@xref{Writing}, for more information on @option{--extract} and
@smallexample
$ @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
+-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 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
+-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}:
@xref{Integrity}, for some of the security-related implications
of using this option.
-@include getdate.texi
+@include parse-datetime.texi
@node Formats
@chapter Controlling the Archive Format
falls back to using archive name suffix to determine its format
(@pxref{auto-compress}, for a list of recognized suffixes).
+@anchor{alternative decompression programs}
+@cindex alternative decompression programs
+Some compression programs are able to handle different compression
+formats. @GNUTAR{} uses this, if the principal decompressor for the
+given format is not available. For example, if @command{compress} is
+not installed, @command{tar} will try to use @command{gzip}. As of
+version @value{VERSION} the following alternatives are
+tried@footnote{To verbosely trace the decompressor selection, use the
+@option{--warning=decompress-program} option
+(@pxref{warnings,decompress-program}).}:
+
+@multitable @columnfractions 0.3 0.3 0.3
+@headitem Format @tab Main decompressor @tab Alternatives
+@item compress @tab compress @tab gzip
+@item lzma @tab lzma @tab xz
+@item bzip2 @tab bzip2 @tab lbzip2
+@end multitable
+
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{}
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.
+When @option{--dereference} (@option{-h}) is used with
+@option{--create} (@option{-c}), @command{tar} archives the files
+symbolic links point to, instead of
+the links themselves.
-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
+When creating portable archives, use @option{--dereference}
+(@option{-h}): some systems do not support
symbolic links, and moreover, your distribution might be unusable if
it contains unresolved symbolic links.
-The @option{--dereference} option is not secure if an untrusted user
-can modify files during creation or extraction. @xref{Security}.
+When reading from an archive, the @option{--dereference} (@option{-h})
+option causes @command{tar} to follow an already-existing symbolic
+link when @command{tar} writes or reads a file named in the archive.
+Ordinarily, @command{tar} does not follow such a link, though it may
+remove the link before writing a new file. @xref{Dealing with Old
+Files}.
+
+The @option{--dereference} option is unsafe if an untrusted user can
+modify directories while @command{tar} is running. @xref{Security}.
@node hard links
@subsection Hard Links
@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
+$ ls -l
+-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
@smallexample
@group
$ @kbd{tar --verbose --list --file=iamanarchive}
-V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
--rw-r--r-- ringo user 40 1990-05-21 13:30 iamafilename
+V--------- 0/0 0 1992-03-07 12:01 iamalabel--Volume Header--
+-rw-r--r-- ringo/user 40 1990-05-21 13:30 iamafilename
@end group
@end smallexample