freebsd-skq/usr.bin/tar/bsdtar.1

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.Dd April 13, 2004
.Dt BSDTAR 1
.Os
.Sh NAME
.Nm bsdtar
.Nd manipulate tape archives
.Sh SYNOPSIS
.Nm
.Op Ar bundled-flags Ao args Ac
.Op Ao Ar file Ac | Ao Ar pattern Ac ...
.Nm
.Brq Fl c
.Op Ar options
.Op Ar files | directories
.Nm
.Brq Fl r | Fl u
.Fl f Ar archive-file
.Op Ar options
.Op Ar files | directories
.Nm
.Brq Fl t | Fl x
.Op Ar options
.Op Ar patterns
.Sh DESCRIPTION
.Nm
creates and manipulates streaming archive files.
.Pp
The first synopsis form shows a
.Dq bundled
option word.
This usage is provided for compatibility with historical implementations.
See COMPATIBILITY below for details.
.Pp
The other synopsis forms show the preferred usage.
The first option to
.Nm
is a mode indicator from the following list:
.Bl -tag -compact -width indent
.It Fl c
Create a new archive containing the specified items.
.It Fl r
Like
.Fl c ,
but new entries are appended to the archive.
Note that this only works on uncompressed archives stored in regular files.
The
.Fl f
option is required.
.It Fl t
List archive contents to stdout.
.It Fl u
Like
.Fl r ,
but new entries are added only if they have a modification date
newer than the corresponding entry in the archive.
Note that this only works on uncompressed archives stored in regular files.
The
.Fl f
option is required.
.It Fl x
Extract to disk from the archive.
If a file with the same name appears more than once in the archive,
each copy will be extracted, with later copies overwriting (replacing)
earlier copies.
.El
.Pp
In
.Fl c ,
.Fl r ,
or
.Fl u
mode, each specified file or directory is added to the
archive in the order specified on the command line.
By default, the contents of each directory are also archived.
.Pp
In extract or list mode, the entire command line
is read and parsed before the archive is opened.
The pathnames or patterns on the command line indicate
which items in the archive should be processed.
Patterns are shell-style globbing patterns as
documented in XXXX.
.Sh OPTIONS
Unless specifically stated otherwise, options are applicable in
all operating modes.
.Bl -tag -width indent
.It Cm @ Ns Pa archive
(c and r mode only)
The specified archive is opened and the entries
in it will be appended to the current archive.
As a simple example,
.Dl Nm Fl c Fl f Pa - Pa newfile Cm @ Ns Pa original.tar
writes a new archive to standard output containing a file
.Pa newfile
and all of the entries from
.Pa original.tar .
In contrast,
.Dl Nm Fl c Fl f Pa - Pa newfile Pa original.tar
creates a new archive with only two entries.
Similarly,
.Dl Nm Fl czf Pa - Fl F Cm pax Cm @ Ns Pa -
reads an archive from standard input (whose format will be determined
automatically) and converts it into a gzip-compressed
pax-format archive on stdout.
In this way,
.Nm
can be used to convert archives from one format to another.
.It Fl b Ar blocksize
Specify the block size, in 512-byte records, for tape drive I/O.
As a rule, this argument is only needed when reading from or writing
to tape drives, and usually not even then as the default block size of
20 records (10240 bytes) is very common.
.It Fl C Ar directory
In c and r mode, this changes the directory before adding
the following files.
In x mode, change directories after opening the archive
but before extracting entries from the archive.
.It Fl -exclude Ar pattern
Do not process files or directories that match the
specified pattern.
Note that exclusions take precedence over patterns or filenames
specified on the command line.
.It Fl F Ar format
(c mode only)
Use the specified format for the created archive.
Supported formats include
.Dq cpio ,
.Dq pax ,
.Dq shar ,
and
.Dq ustar .
Other formats may also be supported; see
.Xr libarchive-formats 5
for more information about currently-supported formats.
.It Fl f Ar file
Read the archive from or write the archive to the specified file.
The filename can be
.Pa -
for standard input or standard output.
If not specified, the default tape device will be used.
(On FreeBSD, the default tape device is
.Pa /dev/sa0 . )
.It Fl -fast-read
(x and t mode only)
Extract or list only the first archive entry that matches each pattern
or filename operand.
Exit as soon as each specified pattern or filename has been matched.
By default, the archive is always read to the very end, since
there can be multiple entries with the same name and, by convention,
later entries overwrite earlier entries.
This option is provided as a performance optimization.
.It Fl H
(c and r mode only)
Symbolic links named on the command line will be followed; the
target of the link will be archived, not the link itself.
.It Fl h
(c and r mode only)
Synonym for
.Fl L .
.It Fl -include Ar pattern
Process only files or directories that match the specified pattern.
Note that exclusions specified with
.Fl -exclude
take precedence over inclusions.
If no inclusions are explicitly specified, all entries are processed by
default.
The
.Fl -include
option is especially useful when filtering archives.
For example, the command
.Dl Nm Fl c Fl f Pa new.tar Fl -include='*foo*' Cm @ Ns Pa old.tgz
creates a new archive
.Pa new.tar
containing only the entries from
.Pa old.tgz
containing the string
.Sq foo .
.It Fl j
(c mode only)
Compress the resulting archive with
.Xr bzip2 1 .
In extract or list modes, this option is ignored.
Note that, unlike other
.Nm tar
implementations, this implementation recognizes bzip2 compression
automatically when reading archives.
.It Fl k
(x mode only)
Do not overwrite existing files.
In particular, if a file appears more than once in an archive,
later copies will not overwrite earlier copies.
.It Fl L
(c and r mode only)
All symbolic links will be followed.
Normally, symbolic links are archived as such.
With this option, the target of the link will be archived instead.
.It Fl l
(c mode only)
Issue a warning message unless all links to each file are archived.
.It Fl m
(x mode only)
Do not extract modification time.
By default, the modification time is set to the time stored in the archive.
.It Fl n
(c, r, u modes only)
Do not recursively archive the contents of directories.
.It Fl -nodump
(c and r modes only)
Honor the nodump file flag by skipping this file.
.It Fl O
(x mode only)
Extracted files are written to standard out rather than
being extracted to disk.
.It Fl o
(x mode only)
Use the user and group of the user running the program rather
than those specified in the archive.
Note that this has no significance unless
.Fl p
is specified, and the program is being run by the root user.
In this case, the file modes and flags from
the archive will be restored, but ACLs or owner information in
the archive will be discarded.
.It Fl P
Preserve pathnames.
By default, absolute pathnames (those that begin with a /
character) have the leading slash removed both when creating archives
and extracting from them.
Also,
.Nm
will refuse to extract archive entries whose pathnames contain
.Pa ..
or whose target directory would be altered by a symlink.
This option suppresses these behaviors.
.It Fl p
(x mode only)
Preserve file permissions.
Attempt to restore the full permissions, including owner, file modes, file
flags and ACLs, if available, for each item extracted from the archive.
By default, newly-created files are owned by the user running
.Nm ,
the file mode is restored for newly-created regular files, and
all other types of entries receive default permissions.
If
.Nm
is being run by root, the default is to restore the owner unless the
.Fl o
option is also specified.
.It Fl T Ar filename
(c mode only)
Read names to be archived from
.Pa filename .
Names are terminated by newlines.
The special name
.Dq -C
will cause the current directory to be changed to the directory
specified on the following line.
.It Fl U
(x mode only)
Unlink files before creating them.
Without this option,
.Nm
overwrites existing files, which preserves existing hardlinks.
With this option, existing hardlinks will be broken, as will any
symlink that would affect the location of an extracted file.
.It Fl v
Produce verbose output.
In create and extract modes,
.Nm
will list each file name as it is read from or written to
the archive.
In list mode,
.Nm
will produce output similar to that of
.Xr ls 1 .
Additional
.Fl v
options will provide additional detail.
.It Fl w
Ask for confirmation for every action.
.It Fl X
(c, r, u modes)
When visiting subdirectories, ignore any that are on different devices.
.It Fl y
(c mode only)
Compress the resulting archive with
.Xr bzip2 1 .
In extract or list modes, this option is ignored.
Note that, unlike other
.Nm tar
implementations, this implementation recognizes bzip2 compression
automatically when reading archives.
.It Fl z
(c mode only)
Compress the resulting archive with
.Xr gzip 1 .
In extract or list modes, this option is ignored.
Note that, unlike other
.Nm tar
implementations, this implementation recognizes gzip compression
automatically when reading archives.
.El
.Sh EXAMPLES
The following creates a new archive
called
.Ar file.tar
that contains two files
.Ar source.c
and
.Ar source.h :
.Dl Nm Fl czf Pa file.tar Pa source.c Pa source.h
.Pp
To view a detailed table of contents for this
archive:
.Dl Nm Fl tvf Pa file.tar
.Pp
To extract all entries from the archive on
the default tape drive:
.Dl Nm Fl x
.Pp
In create mode, the list of files and directories to be archived
can also include directory change instructions of the form
.Cm -C Ns Pa foo/baz
and archive inclusions of the form
.Cm @ Ns Pa archive-file .
For example, the command line
.Dl Nm Fl c Fl f Pa new.tar Pa foo1 Cm @ Ns Pa old.tgz Cm -C Ns Pa /tmp Pa foo2
will create a new archive
.Pa new.tar .
.Nm
will read the file
.Pa foo1
from the current directory and add it to the output archive.
It will then read each entry from
.Pa old.tgz
and add those entries to the output archive.
Finally, it will switch to the
.Pa /tmp
directory and add
.Pa foo2
to the output archive.
.Sh DIAGNOSTICS
.Ex -std
.Sh ENVIRONMENT
The following environment variables affect the execution of
.Nm :
.Bl -tag -width ".Ev BLOCKSIZE"
.It Ev LANG
The locale to use.
See
.Xr environ 7
for more information.
.It Ev TZ
The timezone to use when displaying dates.
See
.Xr environ 7
for more information.
.El
.Sh COMPATIBILITY
The bundled-arguments format is supported for compatibility
with historic implementations.
It consists of an initial word (with no leading - character) in which
each character indicates an option.
Arguments follow as separate words.
The order of the arguments must match the order
of the corresponding characters in the bundled command word.
For example,
.Dl Nm Cm tbf 32 Pa file.tar
specifies three flags
.Cm t ,
.Cm b ,
and
.Cm f .
The
.Cm b
and
.Cm f
flags both require arguments,
so there must be two additional items
on the command line.  The
.Ar 32
is the argument to the
.Cm b
flag, and
.Ar file.tar
is the argument to the
.Cm f
flag.
.Pp
The mode options c, r, t, u, and x and the options
b, f, l, m, o, v, and w comply with SUSv2.
.Pp
For maximum portability, scripts that invoke
.Nm tar
should use the bundled-argument format above, should limit
themselves to the
.Cm c ,
.Cm t ,
and
.Cm x
modes, and the
.Cm b ,
.Cm f ,
.Cm m ,
.Cm v ,
and
.Cm w
options.
.Pp
On systems that support getopt_long(), additional long options
are available to improve compatibility with other tar implementations.
.Sh SECURITY
Certain security issues are common to many archiving programs, including
.Nm .
In particular, carefully-crafted archives can request
.Nm
to extract files to locations outside of the target directory.
This can potentially be used to cause unwitting users to overwrite
files they did not intend to overwrite.
If the archive is being extracted by the superuser, any file
on the system can potentially be overwritten.
There are three ways this can happen.
Although
.Nm
has mechanisms to protect against each one,
savvy users should be aware of the implications:
.Bl -bullet -width indent
.It
Archive entries can have absolute pathnames.
By default,
.Nm
removes the leading
.Pa /
character from filenames before restoring them to gaurd against this problem.
.It
Archive entries can have pathnames that include
.Pa ..
components.
By default,
.Nm
will not extract files containing
.Pa ..
components in their pathname.
.It
Archive entries can exploit symbolic links to restore
files to other directories.
An archive can restore a symbolic link to another directory,
then use that link to restore a file into that directory.
To gaurd against this,
.Nm
checks each extracted path for symlinks.
If the final path element is a symlink, it will be removed
and replaced with the archive entry.
If
.Fl U
is specified, any intermediate symlink will also be unconditionally removed.
If neither
.Fl U
nor
.Fl P
is specified,
.Nm
will refuse to extract the entry.
.El
To protect yourself, you should be wary of any archives that
come from untrusted sources.
You should examine the contents of an archive with
.Dl Nm Fl tf Pa filename
before extraction.
You should use the
.Fl k
option to ensure that
.Nm
will not overwrite any existing files or the
.Fl U
option to remove any pre-existing files.
You should generally not extract archives while running with super-user
privileges.
Note that the
.Fl P
option to
.Nm
disables the security checks above and allows you to extract
an archive while preserving any absolute pathnames,
.Pa ..
components, or symlinks to other directories.
.Sh SEE ALSO
.Xr bzip2 1 ,
.Xr cpio 1 ,
.Xr gzip 1 ,
.Xr mt 1 ,
.Xr pax 1 ,
.Xr shar 1 ,
.Xr libarchive 3 ,
.Xr libarchive-formats 5 ,
.Xr tar 5 .
.Sh STANDARDS
There is no current POSIX standard for the tar command; it appeared
in
.St -p1003.1-1997
but was dropped from
.St -p1003.1-2001 .
The options used by this implementation were developed by surveying a
number of existing tar implementations as well as the old POSIX specification
for tar and the current POSIX specification for pax.
.Pp
The ustar and pax interchange file formats are defined by
.St -p1003.1-2001
for the pax command.
.Sh BUGS
The
.Fl l
and
.Fl o
options follow POSIX.
GNU tar's
.Fl l
and
.Fl o
options do not.
(This is, of course, a bug in GNU tar and not bsdtar.)
.Pp
The
.Fl C Pa dir
option may differ from historic implementations.
.Pp
All archive output is written in correctly-sized blocks, even
if the output is being compressed.
Whether or not the last output block is padded to a full
block size varies depending on the format and the
output device.
For tar and cpio formats, the last block of output is padded
to a full block size if the output is being
written to standard output or to a character or block device such as
a tape drive.
If the output is being written to a regular file, the last block
will not be padded.
Many compressors, including
.Xr gzip 1
and
.Xr bzip2 1 ,
complain about the null padding when decompressing an archive created by
.Nm ,
although they still extract it correctly.
.Pp
The compression and decompression is implemented internally, so
there may be insignificant differences between the compressed output
generated by
.Dl Nm Fl czf Pa - file
and that generated by
.Dl Nm Fl cf Pa - file | Nm gzip
.Pp
The default should be to read and write archives to the standard I/O paths,
but tradition dictates otherwise.
.Pp
The
.Cm r
and
.Cm u
modes require that the archive be uncompressed
and located in a regular file on disk.
Other archives can be modified using
.Cm c
mode with the
.Pa @archive-file
extension.
.Pp
To archive a file called
.Pa @foo
or
.Pa -foo
you must specify it as
.Pa ./@foo
or
.Pa ./-foo ,
respectively.
.Pp
In create mode, a leading
.Pa ./
is always removed.
A leading
.Pa /
is stripped unless the
.Fl P
option is specified.
.Pp
There needs to be better support for file selection on both create
and extract.
.Pp
There is not yet any support for multi-volume archives or sparse files.
.Pp
Converting between dissimilar archive formats (such as tar and cpio) using the
.Cm @ Ns Pa -
convention can cause hard link information to be lost.
(This is a consequence of the incompatible ways that different archive
formats store hardlink information.)
.Pp
All features should be available using only short options in order
to enhance portability to platforms that lack
.Fn getopt_long .
.Pp
There are alternative long options for many of the short options that
are deliberately not documented.
.Sh HISTORY
A
.Nm tar
command appeared in Sixth Edition Unix.
There have been numerous other implementations,
many of which extended the file format.
John Gilmore's
.Nm pdtar
public-domain implementation (circa November, 1987)
was quite influential, and formed the basis of GNU tar.
GNU tar was included as the standard system tar
in FreeBSD beginning with FreeBSD 1.0.
.Pp
This is a complete re-implementation based on the
.Xr libarchive 3
library.