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

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.Dd March 5, 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 | Fl t | Fl x
.Op Ar options
.Op Ar files | patterns | directories
.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 preferred usage is illustrated in the second synopsis.
The first option to
.Nm
must be 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 specified with the
.Fl f
option, which is required.
If a new entry has the same name as an existing entry, it will normally
overwrite (replace) that entry on extraction.
Note that this only works on uncompressed archives stored in regular files.
.It Fl t
List archive contents to stdout.
.It Fl u
Like
.Fl r ,
but new entries are written 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.
.It Fl x
Extract to disk from the archive.
.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
Change directories.
The directory is changed after the archive
is opened, but before any entries are extracted or written.
(In particular, it does not affect the interpretation of the
.Fl f
option.)
In create mode, note that
.Fl C
options are all processed before any files are read.
To change directories between files, use
.Cm C=
instead.
.It Cm C= Ns Pa dir
(c and r mode only)
Change to the specified directory before adding the following files.
(Note that this is not an option in the sense of
.Xr getopt 3 ,
and is therefore processed as the files are processed.)
.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 ,
.Dq shardump ,
and
.Dq ustar .
.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.
.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 j
(c mode only)
Compress the resulting archive with
.Xr bzip2 1 .
Note that, unlike other
.Nm tar
implementations, this implementation recognizes bzip2 compression
automatically when reading archives.
This option is ignored in extract or list modes.
.It Fl k
(x mode only)
Do not overwrite existing files.
.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.
(not yet implemented)
.It Fl P
Preserve leading slashes.
By default, absolute pathnames (those that begin with a / character)
have the leading slash removed.
This option suppresses that behavior.
.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 regular files have the file mode restored and
all other types of entries receive default permissions.
.It Fl U
(x mode only)
Unlink files before creating them.
(Not yet implemented.)
.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 .
.It Fl z
(c mode only)
Compress the resulting archive with
.Xr gzip 1 .
Note that, unlike other
.Nm tar
implementations, this implementation recognizes gzip
and bzip2 compression automatically when reading archives.
The
.Fl j , y , No and Fl z
options are ignored for extract or list mode.
.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 are implemented to be compatible
with SUSv2.
.Pp
On systems that support getopt_long(), additional long options
are available to improve compatibility with other tar implementations.
.Pp
The
.Nm
program reads and writes a variety of streaming archive formats, including:
.Bl -tag -width indent
.It Cm cpio
The octet-oriented cpio format standardized by POSIX.
.It Cm gnutar
.Nm
has limited read support for GNU-format tar archives.
.It Cm pax interchange
The pax interchange format is a POSIX-standard tar format that removes
essentially all of the historic limitations in a standard-conforming fashion.
This format is supported by standard implementations of
.Xr pax 1
as well as by some
.Nm tar
programs, including
.Nm star .
.It Cm shar
A
.Dq shar
format archive is a shell script that, when executed on a POSIX-compliant
system, will recreate the specified files.
Note that shar-format archives will be plain text files only if all of the
files being archived are themselves plain text files.
.It Cm shardump
This format is similar to shar but encodes binary files so that the result
will be a plain text file regardless of the file contents.
It also includes additional shell commands that attempt to reproduce as
many file attributes as possible, including owner, mode, and flags.
.It Cm tar
.Nm
can read most older tar archives, including many that violate
the POSIX standard.
.It Cm ustar
The format first standardized by POSIX.
It has the following limitations:
.Bl -bullet -compact
.It
Device major and minor numbers are limited to 21 bits.
Nodes with larger numbers will not be added to the archive.
.It
Path names in the archive are limited to 255 bytes.
(Shorter if there is no / character in exactly the right place.)
.It
Symbolic links and hard links are stored in the archive with
the name of the referenced file.
This name is limited to 100 bytes.
.It
Extended attributes, file flags, and other extended
security information cannot be stored.
.It
Archive entries are limited to 2 gigabytes in size.
.El
Note that the pax interchange has none of these restrictions.
.Nm
also supports a variety of extensions to this format
used by particular archivers.
In particular, it supports base-256 values in certain numeric fields.
This essentially removes the limitations on file size, modification time,
and device numbers.
.El
.Sh SEE ALSO
.Xr ar 1 ,
.Xr bzip2 1 ,
.Xr gzip 1 ,
.Xr mt 1 ,
.Xr pax 1 ,
.Xr shar 1 ,
.Xr libarchive 3 ,
.Xr tar 5 .
.Sh STANDARDS
There is no current POSIX standard for the tar command; it appeared
in SUSv2 but was dropped from SUSv3.
The options used by this implementation were developed by surveying a
number of existing tar implementations as well as the old SUSv2 specification
for tar and the current SUSv3 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 distinction between the
.Fl C Pa dir
option and the
.Cm C= Ns Pa dir
operation is prompted by the use of
.Xr getopt_long 3
for parsing the command line.
Recall that
.Xr getopt_long 3
processes all options before all non-options.
In particular,
.Cm C= Ns Pa dir
is not an option, and is therefore processed in the order it appears
on the command line.
In contrast,
.Fl C Pa dir
is an option, and therefore, in accordance with POSIX
conventions, is handled in a manner that does not
depend on the order of command-line options.
This behavior differs from that of implementations that do
not follow standard getopt argument parsing conventions.
.Pp
Since many options depend on the particular operating mode,
the mode option itself must be specified first on the command line.
This allows for more accurate detection and reporting of
incorrect option usage.
.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 C=foo ,
you must specify it as
.Pa ./C=foo
on the command line.
Similarly, 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
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.