tar
The GNU tar program is invoked as either one of:
tar option... [name]... tar letter... [argument]... [option]... [name]...
The second form is for when old options are being used.
You can use tar to store files in an archive, to extract them from
an archive, and to do other types of archive manipulation. The primary
argument to tar, which is called the operation, specifies
which action to take. The other arguments to tar are either
options, which change the way tar performs an operation,
or file names or archive members, which specify the files or members
tar is to act on.
You can actually type in arguments in any order, even if in this manual
the options always precede the other arguments, to make examples easier
to understand. Further, the option stating the main operation mode
(the tar main command) is usually given first.
Each name in the synopsis above is interpreted as an archive member
name when the main command is one of --compare (--diff, -d), --delete,
--extract (--get, -x), --list (-t) or --update (-u). When naming
archive members, you must give the exact name of the member in the
archive, as it is printed by --list (-t). For --append (-r)
and --create (-c), these name arguments specify the names
of either files or directory hierarchies to place in the archive.
These files or hierarchies should already exist in the file system,
prior to the execution of the tar command.
tar interprets relative file names as being relative to the
working directory. tar will make all file names relative
(by removing leading slashes when archiving or restoring files),
unless you specify otherwise (using the --absolute-names (-P)
option). See section Absolute File Names, for more information about
--absolute-names (-P).
If you give the name of a directory as either a file name or a member
name, then tar acts recursively on all the files and directories
beneath that directory. For example, the name `/' identifies all
the files in the filesystem to tar.
The distinction between file names and archive member names is especially
important when shell globbing is used, and sometimes a source of confusion
for newcomers. See section Wildcards Patterns and Matching, for more information about globbing.
The problem is that shells may only glob using existing files in the
file system. Only tar itself may glob on archive members, so when
needed, you must ensure that wildcard characters reach tar without
being interpreted by the shell first. Using a backslash before `*'
or `?', or putting the whole argument between quotes, is usually
sufficient for this.
Even if names are often specified on the command line, they can also be read from a text file in the file system, using the --files-from=file-of-names (-T file-of-names) option.
If you don't use any file name arguments, --append (-r),
--delete and --concatenate (--catenate, -A) will do nothing, while
--create (-c) will usually yield a diagnostic and inhibit tar
execution. The other operations of tar (--list (-t),
--extract (--get, -x), --compare (--diff, -d), and --update (-u)) will act
on the entire contents of the archive.
Besides successful exits, GNU tar may fail for many reasons.
Some reasons correspond to bad usage, that is, when the tar
command is improperly written.
Errors may be encountered later, while encountering an error
processing the archive or the files. Some errors are recoverable,
in which case the failure is delayed until tar has completed
all its work. Some errors are such that it would not meaningful,
or at least risky, to continue processing: tar then aborts
processing immediately. All abnormal exits, whether immediate or
delayed, should always be clearly diagnosed on stderr, after
a line stating the nature of the error.
GNU tar returns only a few exit statuses. I'm really
aiming simplicity in that area, for now. If you are not using the
--compare (--diff, -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.
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