BSDTAR(1) MidnightBSD General Commands Manual BSDTAR(1)

NAME

tar — manipulate tape archives

SYNOPSIS

tar [bundled-flags 

args 〉] [〈
file
〉 | 〈
pattern
〉 ...]

tar {−c} [options] [files directories]
tar
{−r −u} −f archive-file [options] [files directories]
tar
{−t −x} [options] [patterns]

DESCRIPTION

tar creates and manipulates streaming archive files. This implementation can extract from tar, pax, cpio, zip, jar, ar, and ISO 9660 cdrom images and can create tar, pax, cpio, ar, and shar archives.

The first synopsis form shows a ‘‘bundled’’ option word. This usage is provided for compatibility with historical implementations. See COMPATIBILITY below for details.

The other synopsis forms show the preferred usage. The first option to tar is a mode indicator from the following list:

−c

Create a new archive containing the specified items.

−r

Like −c, but new entries are appended to the archive. Note that this only works on uncompressed archives stored in regular files. The −f option is required.

−t

List archive contents to stdout.

−u

Like −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 −f option is required.

−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.

In −c, −r, or −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.

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 tcsh(1).

OPTIONS

Unless specifically stated otherwise, options are applicable in all operating modes.

@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,

tar −c −f - newfile @original.tar

writes a new archive to standard output containing a file newfile and all of the entries from original.tar. In contrast,

tar −c −f - newfile original.tar

creates a new archive with only two entries. Similarly,

tar −czf - −-format pax @-

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, tar can be used to convert archives from one format to another.

−b 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.

−C 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.

−-check-links (−W check-links)

(c and r modes only) Issue a warning message unless all links to each file are archived.

−-chroot (−W chroot)

(x mode only) chroot() to the current directory after processing any −C options and before extracting any files.

−-exclude pattern (−W exclude=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.

−-format format (−W format=format)

(c, r, u mode only) Use the specified format for the created archive. Supported formats include ‘‘cpio’’, ‘‘pax’’, ‘‘shar’’, and ‘‘ustar’’. Other formats may also be supported; see libarchive-formats(5) for more information about currently-supported formats. In r and u modes, when extending an existing archive, the format specified here must be compatible with the format of the existing archive on disk.

−f file

Read the archive from or write the archive to the specified file. The filename can be - for standard input or standard output. If not specified, the default tape device will be used. (On FreeBSD, the default tape device is /dev/sa0.)

−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.

−h

(c and r mode only) Synonym for −L.

−I

Synonym for −T.

−-include pattern (−W include=pattern)

Process only files or directories that match the specified pattern. Note that exclusions specified with −-exclude take precedence over inclusions. If no inclusions are explicitly specified, all entries are processed by default. The −-include option is especially useful when filtering archives. For example, the command

tar −c −f new.tar −-include=’*foo*’ @old.tgz

creates a new archive new.tar containing only the entries from old.tgz containing the string ‘foo’.

−j

(c mode only) Compress the resulting archive with bzip2(1). In extract or list modes, this option is ignored. Note that, unlike other tar implementations, this implementation recognizes bzip2 compression automatically when reading archives.

−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.

−-keep-newer-files (−W keep-newer-files)

(x mode only) Do not overwrite existing files that are newer than the versions appearing in the archive being extracted.

−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.

−l

This is a synonym for the −-check-links option.

−m

(x mode only) Do not extract modification time. By default, the modification time is set to the time stored in the archive.

−n

(c, r, u modes only) Do not recursively archive the contents of directories.

−-newer date (−W newer=date)

(c, r, u modes only) Only include files and directories newer than the specified date. This compares ctime entries.

−-newer-mtime date (−W newer-mtime=date)

(c, r, u modes only) Like −-newer, except it compares mtime entries instead of ctime entries.

−-newer-than file (−W newer-than=file)

(c, r, u modes only) Only include files and directories newer than the specified file. This compares ctime entries.

−-newer-mtime-than file (−W newer-mtime-than=file)

(c, r, u modes only) Like −-newer-than, except it compares mtime entries instead of ctime entries.

−-nodump (−W nodump)

(c and r modes only) Honor the nodump file flag by skipping this file.

−-null (−W null)

(use with −I, −T, or −X) Filenames or patterns are separated by null characters, not by newlines. This is often used to read filenames output by the −print0 option to find(1).

−-numeric-owner

(x mode only) Ignore symbolic user and group names when restoring archives to disk, only numeric uid and gid values will be obeyed.

−O

(x, t modes only) In extract (-x) mode, files will be written to standard out rather than being extracted to disk. In list (-t) mode, the file listing will be written to stderr rather than the usual stdout.

−o

(x mode) 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 −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.

−o

(c, r, u mode) A synonym for −-format ustar

−-one-file-system (−W one-file-system)

(c, r, and u modes) Do not cross mount points.

−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, tar will refuse to extract archive entries whose pathnames contain .. or whose target directory would be altered by a symlink. This option suppresses these behaviors.

−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 tar, the file mode is restored for newly-created regular files, and all other types of entries receive default permissions. If tar is being run by root, the default is to restore the owner unless the −o option is also specified.

−q (−-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.

−S

(x mode only) Extract files as sparse files. For every block on disk, check first if it contains only NULL bytes and seek over it otherwise. This works similiar to the conv=sparse option of dd.

−-strip-components count (−W strip-components=count)

(x and t mode only) Remove the specified number of leading path elements. Pathnames with fewer elements will be silently skipped. Note that the pathname is edited after checking inclusion/exclusion patterns but before security checks.

−s pattern

Modify file or archive member names according to pattern. The pattern has the format /old/new/[gps]. old is a basic regular expression. If it doesn’t apply, the pattern is skipped. new is the replacement string of the matched part. ~ is substituted with the match, 1 to 9 with the content of the corresponding captured group. The optional trailing g specifies that matching should continue after the matched part and stopped on the first unmatched pattern. The optional trailing s specifies that the pattern applies to the value of symbolic links. The optional trailing p specifies that after a successful substitution the original path name and the new path name should be printed to standard error.

−T filename

In x or t mode, tar will read the list of names to be extracted from filename. In c mode, tar will read names to be archived from filename. The special name ‘‘-C’’ on a line by itself will cause the current directory to be changed to the directory specified on the following line. Names are terminated by newlines unless −-null is specified. Note that −-null also disables the special handling of lines containing ‘‘-C’’.

−U

(x mode only) Unlink files before creating them. Without this option, tar 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.

−-use-compress-program program

Pipe the input (in x or t mode) or the output (in c mode) through program instead of using the builtin compression support.

−v

Produce verbose output. In create and extract modes, tar will list each file name as it is read from or written to the archive. In list mode, tar will produce output similar to that of ls(1). Additional −v options will provide additional detail.

−-version

Print version of tar and libarchive, and exit.

−W longopt=value

Long options (preceded by −−) are only supported directly on systems that have the getopt_long(3) function. The −W option can be used to access long options on systems that do not support this function.

−w

Ask for confirmation for every action.

−X filename

Read a list of exclusion patterns from the specified file. See −-exclude for more information about the handling of exclusions.

−y

(c mode only) Compress the resulting archive with bzip2(1). In extract or list modes, this option is ignored. Note that, unlike other tar implementations, this implementation recognizes bzip2 compression automatically when reading archives.

−z

(c mode only) Compress the resulting archive with gzip(1). In extract or list modes, this option is ignored. Note that, unlike other tar implementations, this implementation recognizes gzip compression automatically when reading archives.

−Z

(c mode only) Compress the resulting archive with compress(1). In extract or list modes, this option is ignored. Note that, unlike other tar implementations, this implementation recognizes compress compression automatically when reading archives.

ENVIRONMENT

The following environment variables affect the execution of tar:

LANG

The locale to use. See environ(7) for more information.

TAPE

The default tape device. The −f option overrides this.

TZ

The timezone to use when displaying dates. See environ(7) for more information.

FILES
/dev/sa0

The default tape device, if not overridden by the TAPE environment variable or the −f option.

EXIT STATUS

The tar utility exits 0 on success, and >0 if an error occurs.

EXAMPLES

The following creates a new archive called file.tar.gz that contains two files source.c and source.h:

tar −czf file.tar.gz source.c source.h

To view a detailed table of contents for this archive:

tar −tvf file.tar.gz

To extract all entries from the archive on the default tape drive:

tar −x

To examine the contents of an ISO 9660 cdrom image:

tar −tf image.iso

To move file hierarchies, invoke tar as

tar −cf - −C srcdir . | tar −xpf - −C destdir

or more traditionally

cd srcdir ; tar −cf - . | (cd destdir ; tar −xpf -)

In create mode, the list of files and directories to be archived can also include directory change instructions of the form -Cfoo/baz and archive inclusions of the form @archive-file. For example, the command line

tar −c −f new.tar foo1 @old.tgz -C/tmp foo2

will create a new archive new.tar. tar will read the file foo1 from the current directory and add it to the output archive. It will then read each entry from old.tgz and add those entries to the output archive. Finally, it will switch to the /tmp directory and add foo2 to the output archive.

An input file in mtree(5) format can be used to create an output archive with arbitrary ownership, permissions, or names that differ from existing data on disk:

$ cat input.mtree
#mtree
usr/bin uid=0 gid=0 mode=0755 type=dir
usr/bin/ls uid=0 gid=0 mode=0755 type=file content=myls
$ tar -cvf output.tar @input.mtree

The −-newer and −-newer-mtime switches accept a variety of common date and time specifications, including ‘‘12 Mar 2005 7:14:29pm’’, ‘‘2005-03-12 19:14’’, ‘‘5 minutes ago’’, and ‘‘19:14 PST May 1’’.

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,

tar tbf 32 file.tar

specifies three flags t, b, and f. The b and f flags both require arguments, so there must be two additional items on the command line. The 32 is the argument to the b flag, and file.tar is the argument to the f flag.

The mode options c, r, t, u, and x and the options b, f, l, m, o, v, and w comply with SUSv2.

For maximum portability, scripts that invoke tar should use the bundled-argument format above, should limit themselves to the c, t, and x modes, and the b, f, m, v, and w options.

On systems that support getopt_long(), additional long options are available to improve compatibility with other tar implementations.

SECURITY

Certain security issues are common to many archiving programs, including tar. In particular, carefully-crafted archives can request that tar 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 tar has mechanisms to protect against each one, savvy users should be aware of the implications:

Archive entries can have absolute pathnames. By default, tar removes the leading / character from filenames before restoring them to guard against this problem.

Archive entries can have pathnames that include .. components. By default, tar will not extract files containing .. components in their pathname.

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 guard against this, tar 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 −U is specified, any intermediate symlink will also be unconditionally removed. If neither −U nor −P is specified, tar will refuse to extract the entry.

To protect yourself, you should be wary of any archives that come from untrusted sources. You should examine the contents of an archive with

tar −tf filename

before extraction. You should use the −k option to ensure that tar will not overwrite any existing files or the −U option to remove any pre-existing files. You should generally not extract archives while running with super-user privileges. Note that the −P option to tar disables the security checks above and allows you to extract an archive while preserving any absolute pathnames, .. components, or symlinks to other directories.

SEE ALSO

bzip2(1), compress(1), cpio(1), gzip(1), mt(1), pax(1), shar(1), libarchive(3), libarchive-formats(5), tar(5)

STANDARDS

There is no current POSIX standard for the tar command; it appeared in ISO/IEC 9945-1:1996 (‘‘POSIX.1’’) but was dropped from IEEE Std 1003.1-2001 (‘‘POSIX.1’’). 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.

The ustar and pax interchange file formats are defined by IEEE Std 1003.1-2001 (‘‘POSIX.1’’) for the pax command.

HISTORY

A tar command appeared in Seventh Edition Unix, which was released in January, 1979. There have been numerous other implementations, many of which extended the file format. John Gilmore’s 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.

This is a complete re-implementation based on the libarchive(3) library.

BUGS

This program follows ISO/IEC 9945-1:1996 (‘‘POSIX.1’’) for the definition of the −l option. Note that GNU tar prior to version 1.15 treated −l as a synonym for the −-one-file-system option.

The −C dir option may differ from historic implementations.

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 gzip(1) and bzip2(1), complain about the null padding when decompressing an archive created by tar, although they still extract it correctly.

The compression and decompression is implemented internally, so there may be insignificant differences between the compressed output generated by

tar −czf - file

and that generated by

tar −cf - file | gzip

The default should be to read and write archives to the standard I/O paths, but tradition (and POSIX) dictates otherwise.

The r and u modes require that the archive be uncompressed and located in a regular file on disk. Other archives can be modified using c mode with the @archive-file extension.

To archive a file called @foo or -foo you must specify it as ./@foo or ./-foo, respectively.

In create mode, a leading ./ is always removed. A leading / is stripped unless the −P option is specified.

There needs to be better support for file selection on both create and extract.

There is not yet any support for multi-volume archives or for archiving sparse files.

Converting between dissimilar archive formats (such as tar and cpio) using the @- convention can cause hard link information to be lost. (This is a consequence of the incompatible ways that different archive formats store hardlink information.)

There are alternative long options for many of the short options that are deliberately not documented.

MidnightBSD 0.3 May 15, 2008 MidnightBSD 0.3