GNU tar: an archiver tool ¶

2.6.1 Preparing a Practice Directory for Examples ¶

To follow along with this and future examples, create a new directory called practice containing files called blues, folk and jazz. The files can contain any information you like: ideally, they should contain information which relates to their names, and be of different lengths. Our examples assume that practice is a subdirectory of your home directory.

Now cd to the directory named practice; practice is now your working directory. (Please note: Although the full file name of this directory is /homedir/practice, in our examples we will refer to this directory as practice; the homedir is presumed.)

In general, you should check that the files to be archived exist where you think they do (in the working directory) by running ls. Because you just created the directory and the files and have changed to that directory, you probably don’t need to do that this time.

It is very important to make sure there isn’t already a file in the working directory with the archive name you intend to use (in this case, ‘collection.tar’), or that you don’t care about its contents. Whenever you use ‘create’, tar will erase the current contents of the file named by --file=archive-name (-f archive-name) if it exists. tar will not tell you if you are about to overwrite an archive unless you specify an option which does this (see Backup options, for the information on how to do so). To add files to an existing archive, you need to use a different option, such as --append (-r); see How to Add Files to Existing Archives: --append for information on how to do this.

2.6.2 Creating the Archive ¶

To place the files blues, folk, and jazz into an archive named collection.tar, use the following command:

$ tar --create --file=collection.tar blues folk jazz

The order of the arguments is not very important, when using long option forms, however you should always remember to use option as the first argument to tar. For example, the following is wrong:

$ tar blues -c folk -f collection.tar jazz
tar: -c: Invalid blocking factor
Try 'tar --help' or 'tar --usage' for more information.

The error message is produced because tar always treats its first argument as an option (or cluster of options), even if it does not start with dash. This is traditional or old option style, called so because all implementations of tar have used it since the very inception of the tar archiver in 1970s. This option style will be explained later (see Old Option Style), for now just remember to always place option as the first argument.

That being said, you could issue the following command:

$ tar --create folk blues --file=collection.tar jazz

However, you can see that this order is harder to understand; this is why we will list the arguments in the order that makes the commands easiest to understand (and we encourage you to do the same when you use tar, to avoid errors).

Note that the sequence --file=collection.tar is considered to be one argument. If you substituted any other string of characters for collection.tar, then that string would become the name of the archive file you create.

The order of the options becomes more important when you begin to use short forms. With short forms, if you type commands in the wrong order (even if you type them correctly in all other ways), you may end up with results you don’t expect. For this reason, it is a good idea to get into the habit of typing options in the order that makes inherent sense. See Short Forms with ‘create’, for more information on this.

In this example, you type the command as shown above: --create is the operation which creates the new archive (collection.tar), and --file is the option which lets you give it the name you chose. The files, blues, folk, and jazz, are now members of the archive, collection.tar (they are file name arguments to the --create operation. See Choosing Files and Names for tar, for the detailed discussion on these.) Now that they are in the archive, they are called archive members, not files. (see members).

When you create an archive, you must specify which files you want placed in the archive. If you do not specify any archive members, GNU tar will complain.

If you now list the contents of the working directory (ls), you will find the archive file listed as well as the files you saw previously:

blues   folk   jazz   collection.tar

Creating the archive ‘collection.tar’ did not destroy the copies of the files in the directory.

Keep in mind that if you don’t indicate an operation, tar will not run and will prompt you for one. If you don’t name any files, tar will complain. You must have write access to the working directory, or else you will not be able to create an archive in that directory.

Caution: Do not attempt to use --create (-c) to add files to an existing archive; it will delete the archive and write a new one. Use --append (-r) instead. See How to Add Files to Existing Archives: --append.

2.6.3 Running --create with --verbose ¶

If you include the --verbose (-v) option on the command line, tar will list the files it is acting on as it is working. In verbose mode, the create example above would appear as:

$ tar --create --verbose --file=collection.tar blues folk jazz
blues
folk
jazz

This example is just like the example we showed which did not use --verbose, except that tar generated three output lines.

In the rest of the examples in this chapter, we will frequently use verbose mode so we can show actions or tar responses that you would otherwise not see, and which are important for you to understand.

2.6.4 Short Forms with ‘create’ ¶

As we said before, the --create (-c) operation is one of the most basic uses of tar, and you will use it countless times. Eventually, you will probably want to use abbreviated (or “short”) forms of options. A full discussion of the three different forms that options can take appears in The Three Option Styles; for now, here is what the previous example (including the --verbose (-v) option) looks like using short option forms:

$ tar -cvf collection.tar blues folk jazz
blues
folk
jazz

As you can see, the system responds the same no matter whether you use long or short option forms.

One difference between using short and long option forms is that, although the exact placement of arguments following options is no more specific when using short forms, it is easier to become confused and make a mistake when using short forms. For example, suppose you attempted the above example in the following way:

$ tar -cfv collection.tar blues folk jazz

In this case, tar will make an archive file called v, containing the files blues, folk, and jazz, because the ‘v’ is the closest “file name” to the -f option, and is thus taken to be the chosen archive file name. tar will try to add a file called collection.tar to the v archive file; if the file collection.tar did not already exist, tar will report an error indicating that this file does not exist. If the file collection.tar does already exist (e.g., from a previous command you may have run), then tar will add this file to the archive. Because the -v option did not get registered, tar will not run under ‘verbose’ mode, and will not report its progress.

The end result is that you may be quite confused about what happened, and possibly overwrite a file. To illustrate this further, we will show you how an example we showed previously would look using short forms.

This example,

$ tar --create folk blues --file=collection.tar jazz

is confusing as it is. It becomes even more so when using short forms:

$ tar -c folk blues -f collection.tar jazz

It would be very easy to put the wrong string of characters immediately following the -f, but doing that could sacrifice valuable data.

For this reason, we recommend that you pay very careful attention to the order of options and placement of file and archive names, especially when using short option forms. Not having the option name written out mnemonically can affect how well you remember which option does what, and therefore where different names have to be placed.

2.6.5 Archiving Directories ¶

You can archive a directory by specifying its directory name as a file name argument to tar. The files in the directory will be archived relative to the working directory, and the directory will be re-created along with its contents when the archive is extracted.

To archive a directory, first move to its superior directory. If you have followed the previous instructions in this tutorial, you should type:

$ cd ..
$

This will put you into the directory which contains practice, i.e., your home directory. Once in the superior directory, you can specify the subdirectory, practice, as a file name argument. To store practice in the new archive file music.tar, type:

$ tar --create --verbose --file=music.tar practice

tar should output:

practice/
practice/blues
practice/folk
practice/jazz
practice/collection.tar

Note that the archive thus created is not in the subdirectory practice, but rather in the current working directory—the directory from which tar was invoked. Before trying to archive a directory from its superior directory, you should make sure you have write access to the superior directory itself, not only the directory you are trying archive with tar. For example, you will probably not be able to store your home directory in an archive by invoking tar from the root directory; See Absolute File Names. (Note also that collection.tar, the original archive file, has itself been archived. tar will accept any file as a file to be archived, regardless of its content. When music.tar is extracted, the archive file collection.tar will be re-written into the file system).

If you give tar a command such as

$ tar --create --file=foo.tar .

tar will report ‘tar: ./foo.tar is the archive; not dumped’. This happens because tar creates the archive foo.tar in the current directory before putting any files into it. Then, when tar attempts to add all the files in the directory . to the archive, it notices that the file ./foo.tar is the same as the archive foo.tar, and skips it. (It makes no sense to put an archive into itself.) GNU tar will continue in this case, and create the archive normally, except for the exclusion of that one file. (Please note: Other implementations of tar may not be so clever; they will enter an infinite loop when this happens, so you should not depend on this behavior unless you are certain you are running GNU tar. In general, it is wise to always place the archive outside of the directory being dumped.)

2.8.1 Extracting an Entire Archive ¶

To extract an entire archive, specify the archive file name only, with no individual file names as arguments. For example,

$ tar -xvf collection.tar

produces this:

-rw-r--r-- myself/user      28 1996-10-18 16:31 jazz
-rw-r--r-- myself/user      21 1996-09-23 16:44 blues
-rw-r--r-- myself/user      20 1996-09-23 16:44 folk

2.8.2 Extracting Specific Files ¶

To extract specific archive members, give their exact member names as arguments, as printed by --list (-t). If you had mistakenly deleted one of the files you had placed in the archive collection.tar earlier (say, blues), you can extract it from the archive without changing the archive’s structure. Its contents will be identical to the original file blues that you deleted.

First, make sure you are in the practice directory, and list the files in the directory. Now, delete the file, ‘blues’, and list the files in the directory again.

You can now extract the member blues from the archive file collection.tar like this:

$ tar --extract --file=collection.tar blues

If you list the files in the directory again, you will see that the file blues has been restored, with its original permissions, data modification times, and owner.¹ (These parameters will be identical to those which the file had when you originally placed it in the archive; any changes you may have made before deleting the file from the file system, however, will not have been made to the archive member.) The archive file, ‘collection.tar’, is the same as it was before you extracted ‘blues’. You can confirm this by running tar with --list (-t).

Remember that as with other operations, specifying the exact member name is important (See Commands That Will Fail, for more examples).

You can extract a file to standard output by combining the above options with the --to-stdout (-O) option (see Writing to Standard Output).

If you give the --verbose option, then --extract will print the names of the archive members as it extracts them.

2.8.3 Extracting Files that are Directories ¶

Extracting directories which are members of an archive is similar to extracting other files. The main difference to be aware of is that if the extracted directory has the same name as any directory already in the working directory, then files in the extracted directory will be placed into the directory of the same name. Likewise, if there are files in the pre-existing directory with the same names as the members which you extract, the files from the extracted archive will replace the files already in the working directory (and possible subdirectories). This will happen regardless of whether or not the files in the working directory were more recent than those extracted (there exist, however, special options that alter this behavior see Changing How tar Writes Files).

However, if a file was stored with a directory name as part of its file name, and that directory does not exist under the working directory when the file is extracted, tar will create the directory.

We can demonstrate how to use --extract to extract a directory file with an example. Change to the practice directory if you weren’t there, and remove the files folk and jazz. Then, go back to the parent directory and extract the archive music.tar. You may either extract the entire archive, or you may extract only the files you just deleted. To extract the entire archive, don’t give any file names as arguments after the archive name music.tar. To extract only the files you deleted, use the following command:

$ tar -xvf music.tar practice/folk practice/jazz
practice/folk
practice/jazz

If you were to specify two --verbose (-v) options, tar would have displayed more detail about the extracted files, as shown in the example below:

$ 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

Because you created the directory with practice as part of the file names of each of the files by archiving the practice directory as practice, you must give practice as part of the file names when you extract those files from the archive.

2.8.4 Extracting Archives from Untrusted Sources ¶

Extracting files from archives can overwrite files that already exist. If you receive an archive from an untrusted source, you should make a new directory and extract into that directory, so that you don’t have to worry about the extraction overwriting one of your existing files. For example, if untrusted.tar came from somewhere else on the Internet, and you don’t necessarily trust its contents, you can extract it as follows:

$ mkdir newdir
$ cd newdir
$ tar -xvf ../untrusted.tar

It is also a good practice to examine contents of the archive before extracting it, using --list (-t) option, possibly combined with --verbose (-v).

2.8.5 Commands That Will Fail ¶

Here are some sample commands you might try which will not work, and why they won’t work.

If you try to use this command,

$ tar -xvf music.tar folk jazz

you will get the following response:

tar: folk: Not found in archive
tar: jazz: Not found in archive

This is because these files were not originally in the parent directory .., where the archive is located; they were in the practice directory, and their file names reflect this:

$ tar -tvf music.tar
practice/blues
practice/folk
practice/jazz

Likewise, if you try to use this command,

$ tar -tvf music.tar folk jazz

you would get a similar response. Members with those names are not in the archive. You must use the correct member names, or wildcards, in order to extract the files from the archive.

If you have forgotten the correct names of the files in the archive, use tar --list --verbose to list them correctly.

To extract the member named practice/folk, you must specify

$ tar --extract --file=music.tar practice/folk

Notice also, that as explained above, the practice directory will be created, if it didn’t already exist. There are options that allow you to strip away a certain number of leading directory components (see Modifying File and Member Names). For example,

$ tar --extract --file=music.tar --strip-components=1 folk

will extract the file folk into the current working directory.

3.3.1 Long Option Style ¶

Each option has at least one long (or mnemonic) name starting with two dashes in a row, e.g., --list. The long names are more clear than their corresponding short or old names. It sometimes happens that a single long option has many different names which are synonymous, such as --compare and --diff. In addition, long option names can be given unique abbreviations. For example, --cre can be used in place of --create because there is no other long option which begins with ‘cre’. (One way to find this out is by trying it and seeing what happens; if a particular abbreviation could represent more than one option, tar will tell you that that abbreviation is ambiguous and you’ll know that that abbreviation won’t work. You may also choose to run ‘tar --help’ to see a list of options. Be aware that if you run tar with a unique abbreviation for the long name of an option you didn’t want to use, you are stuck; tar will perform the command as ordered.)

Long options are meant to be obvious and easy to remember, and their meanings are generally easier to discern than those of their corresponding short options (see below). For example:

$ tar --create --verbose --blocking-factor=20 --file=/dev/rmt0

gives a fairly good set of hints about what the command does, even for those not fully acquainted with tar.

Long options which require arguments take those arguments immediately following the option name. There are two ways of specifying a mandatory argument. It can be separated from the option name either by an equal sign, or by any amount of white space characters. For example, the --file option (which tells the name of the tar archive) is given a file such as archive.tar as argument by using any of the following notations: --file=archive.tar or --file archive.tar.

In contrast, optional arguments must always be introduced using an equal sign. For example, the --backup option takes an optional argument specifying backup type. It must be used as --backup=backup-type.

3.3.2 Short Option Style ¶

Most options also have a short option name. Short options start with a single dash, and are followed by a single character, e.g., -t (which is equivalent to --list). The forms are absolutely identical in function; they are interchangeable.

The short option names are faster to type than long option names.

Short options which require arguments take their arguments immediately following the option, usually separated by white space. It is also possible to stick the argument right after the short option name, using no intervening space. For example, you might write -f archive.tar or -farchive.tar instead of using --file=archive.tar. Both --file=archive-name and -f archive-name denote the option which indicates a specific archive, here named archive.tar.

Short options which take optional arguments take their arguments immediately following the option letter, without any intervening white space characters.

Short options’ letters may be clumped together, but you are not required to do this (as compared to old options; see below). When short options are clumped as a set, use one (single) dash for them all, e.g., ‘tar -cvf’. Only the last option in such a set is allowed to have an argument³.

When the options are separated, the argument for each option which requires an argument directly follows that option, as is usual for Unix programs. For example:

$ tar -c -v -b 20 -f /dev/rmt0

If you reorder short options’ locations, be sure to move any arguments that belong to them. If you do not move the arguments properly, you may end up overwriting files.

3.3.3 Old Option Style ¶

As far as we know, all tar programs, GNU and non-GNU, support old options: that is, if the first argument does not start with ‘-’, it is assumed to specify option letters. GNU tar supports old options not only for historical reasons, but also because many people are used to them. If the first argument does not start with a dash, you are announcing the old option style instead of the short option style; old options are decoded differently.

Like short options, old options are single letters. However, old options must be written together as a single clumped set, without spaces separating them or dashes preceding them. This set of letters must be the first to appear on the command line, after the tar program name and some white space; old options cannot appear anywhere else. The letter of an old option is exactly the same letter as the corresponding short option. For example, the old option ‘t’ is the same as the short option -t, and consequently, the same as the long option --list. So for example, the command ‘tar cv’ specifies the option -v in addition to the operation -c.

When options that need arguments are given together with the command, all the associated arguments follow, in the same order as the options. Thus, the example given previously could also be written in the old style as follows:

$ tar cvbf 20 /dev/rmt0

Here, ‘20’ is the argument of -b and ‘/dev/rmt0’ is the argument of -f.

The old style syntax can make it difficult to match option letters with their corresponding arguments, and is often confusing. In the command ‘tar cvbf 20 /dev/rmt0’, for example, ‘20’ is the argument for -b, ‘/dev/rmt0’ is the argument for -f, and -v does not have a corresponding argument. Even using short options like in ‘tar -c -v -b 20 -f /dev/rmt0’ is clearer, putting all arguments next to the option they pertain to.

If you want to reorder the letters in the old option argument, be sure to reorder any corresponding argument appropriately.

This old way of writing tar options can surprise even experienced users. For example, the two commands:

tar cfz archive.tar.gz file
tar -cfz archive.tar.gz file

are quite different. The first example uses archive.tar.gz as the value for option ‘f’ and recognizes the option ‘z’. The second example, however, uses z as the value for option ‘f’ — probably not what was intended.

This second example could be corrected in many ways, among which the following are equivalent:

tar -czf archive.tar.gz file
tar -cf archive.tar.gz -z file
tar cf archive.tar.gz -z file

3.3.4 Mixing Option Styles ¶

All three styles may be intermixed in a single tar command, so long as the rules for each style are fully respected⁴. Old style options and either of the modern styles of options may be mixed within a single tar command. However, old style options must be introduced as the first arguments only, following the rule for old options (old options must appear directly after the tar command and some white space). Modern options may be given only after all arguments to the old options have been collected. If this rule is not respected, a modern option might be falsely interpreted as the value of the argument to one of the old style options.

For example, all the following commands are wholly equivalent, and illustrate the many combinations and orderings of option styles.

tar --create --file=archive.tar
tar --create -f archive.tar
tar --create -farchive.tar
tar --file=archive.tar --create
tar --file=archive.tar -c
tar -c --file=archive.tar
tar -c -f archive.tar
tar -c -farchive.tar
tar -cf archive.tar
tar -cfarchive.tar
tar -f archive.tar --create
tar -f archive.tar -c
tar -farchive.tar --create
tar -farchive.tar -c
tar c --file=archive.tar
tar c -f archive.tar
tar c -farchive.tar
tar cf archive.tar
tar f archive.tar --create
tar f archive.tar -c
tar fc archive.tar

On the other hand, the following commands are not equivalent to the previous set:

tar -f -c archive.tar
tar -fc archive.tar
tar -fcarchive.tar
tar -farchive.tarc
tar cfarchive.tar

These last examples mean something completely different from what the user intended (judging based on the example in the previous set which uses long options, whose intent is therefore very clear). The first four specify that the tar archive would be a file named -c, ‘c’, ‘carchive.tar’ or ‘archive.tarc’, respectively. The first two examples also specify a single non-option, name argument having the value ‘archive.tar’. The last example contains only old style option letters (repeating option ‘c’ twice), not all of which are meaningful (eg., ‘.’, ‘h’, or ‘i’), with no argument value.

3.4.1 Operations ¶

--append ¶

-r

Appends files to the end of the archive. See How to Add Files to Existing Archives: --append.

--catenate ¶

-A

Same as --concatenate. See Combining Archives with --concatenate.

--compare ¶

-d

Compares archive members with their counterparts in the file system, and reports differences in file size, mode, owner, modification date and contents. See Comparing Archive Members with the File System.

--concatenate ¶

-A

Appends other tar archives to the end of the archive. See Combining Archives with --concatenate.

--create ¶

-c

Creates a new tar archive. See How to Create Archives.

--delete ¶

Deletes members from the archive. Don’t try this on an archive on a tape! See Removing Archive Members Using --delete.

--diff ¶

-d

Same as --compare. See Comparing Archive Members with the File System.

--extract ¶

-x

Extracts members from the archive into the file system. See How to Extract Members from an Archive.

--get ¶

-x

Same as --extract. See How to Extract Members from an Archive.

--list ¶

-t

Lists the members in an archive. See How to List Archives.

--update ¶

-u

Adds files to the end of the archive, but only if they are newer than their counterparts already in the archive, or if they do not already exist in the archive. See Updating an Archive.

3.4.2 tar Options ¶

--absolute-names ¶

-P

Normally when creating an archive, tar strips an initial ‘/’ from member names, and when extracting from an archive tar treats names specially if they have initial ‘/’ or internal ‘..’. This option disables that behavior. See Absolute File Names.

--acls ¶

Enable POSIX ACLs support. See acls.

--after-date ¶

(See --newer, see Operating Only on New Files)

--anchored ¶

A pattern must match an initial subsequence of the name’s components. See Controlling Pattern-Matching.

--atime-preserve ¶

--atime-preserve=replace

--atime-preserve=system

Attempt to preserve the access time of files when reading them. This option currently is effective only on files that you own, unless you have superuser privileges.

--atime-preserve=replace remembers the access time of a file before reading it, and then restores the access time afterwards. This may cause problems if other programs are reading the file at the same time, as the times of their accesses will be lost. On most platforms restoring the access time also requires tar to restore the data modification time too, so this option may also cause problems if other programs are writing the file at the same time (tar attempts to detect this situation, but cannot do so reliably due to race conditions). Worse, on most platforms restoring the access time also updates the status change time, which means that this option is incompatible with incremental backups.

--atime-preserve=system avoids changing time stamps on files, without interfering with time stamp updates caused by other programs, so it works better with incremental backups. However, it requires a special O_NOATIME option from the underlying operating and file system implementation, and it also requires that searching directories does not update their access times. As of this writing (November 2005) this works only with Linux, and only with Linux kernels 2.6.8 and later. Worse, there is currently no reliable way to know whether this feature actually works. Sometimes tar knows that it does not work, and if you use --atime-preserve=system then tar complains and exits right away. But other times tar might think that the option works when it actually does not.

Currently --atime-preserve with no operand defaults to --atime-preserve=replace, but this may change in the future as support for --atime-preserve=system improves.

If your operating or file system does not support --atime-preserve=system, you might be able to preserve access times reliably by using the mount command. For example, you can mount the file system read-only, or access the file system via a read-only loopback mount, or use the ‘noatime’ mount option available on some systems. However, mounting typically requires superuser privileges and can be a pain to manage.

--auto-compress ¶

-a

During a --create operation, enables automatic compressed format recognition based on the archive suffix. The effect of this option is cancelled by --no-auto-compress. See Creating and Reading Compressed Archives.

--backup=backup-type ¶

Rather than deleting files from the file system, tar will back them up using simple or numbered backups, depending upon backup-type. See Backup options.

--block-number ¶

-R

With this option present, tar prints error messages for read errors with the block number in the archive file. See block-number.

--blocking-factor=blocking ¶

-b blocking

Sets the blocking factor tar uses to blocking x 512 bytes per record. See The Blocking Factor of an Archive.

--bzip2 ¶

-j

This option tells tar to read or write archives through bzip2. See Creating and Reading Compressed Archives.

--check-device ¶

Check device numbers when creating a list of modified files for incremental archiving. This is the default. See device numbers, for a detailed description.

--checkpoint[=number] ¶

This option directs tar to print periodic checkpoint messages as it reads through the archive. It is intended for when you want a visual indication that tar is still running, but don’t want to see --verbose output. You can also instruct tar to execute a list of actions on each checkpoint, see --checkpoint-action below. For a detailed description, see Checkpoints.

--checkpoint-action=action ¶

Instruct tar to execute an action upon hitting a breakpoint. Here we give only a brief outline. See Checkpoints, for a complete description.

The action argument can be one of the following:

bell

Produce an audible bell on the console.

dot

.

Print a single dot on the standard listing stream.

echo

Display a textual message on the standard error, with the status and number of the checkpoint. This is the default.

echo=string

Display string on the standard error. Before output, the string is subject to meta-character expansion.

exec=command

Execute the given command.

sleep=time

Wait for time seconds.

ttyout=string

Output string on the current console (/dev/tty).

totals

Print statistics (see see totals).

wait=signo

Wait for signal signo.

Several --checkpoint-action options can be specified. The supplied actions will be executed in order of their appearance in the command line.

Using --checkpoint-action without --checkpoint assumes default checkpoint frequency of one checkpoint per 10 records.

--check-links ¶

-l

If this option was given, tar will check the number of links dumped for each processed file. If this number does not match the total number of hard links for the file, a warning message will be output ⁵.

See Hard Links.

--compress ¶

--uncompress

-Z

tar will use the compress program when reading or writing the archive. This allows you to directly act on archives while saving space. See Creating and Reading Compressed Archives.

--clamp-mtime ¶

(See --mtime.)

--confirmation ¶

(See --interactive.) See Asking for Confirmation During Operations.

--delay-directory-restore ¶

Delay setting modification times and permissions of extracted directories until the end of extraction. See Directory Modification Times and Permissions.

--dereference ¶

-h

When reading or writing a file to be archived, tar accesses the file that a symbolic link points to, rather than the symlink itself. See Symbolic Links.

--directory=dir ¶

-C dir

When this option is specified, tar will change its current directory to dir before performing any operations. When this option is used during archive creation, it is order sensitive. See Changing the Working Directory.

--exclude=pattern ¶

When performing operations, tar will skip files that match pattern. See Excluding Some Files.

--exclude-backups ¶

Exclude backup and lock files. See exclude-backups.

--exclude-from=file ¶

-X file

Similar to --exclude, except tar will use the list of patterns in the file file. See Excluding Some Files.

--exclude-caches ¶

Exclude from dump any directory containing a valid cache directory tag file, but still dump the directory node and the tag file itself.

See exclude-caches.

--exclude-caches-under ¶

Exclude from dump any directory containing a valid cache directory tag file, but still dump the directory node itself.

See Excluding Some Files.

--exclude-caches-all ¶

Exclude from dump any directory containing a valid cache directory tag file. See Excluding Some Files.

--exclude-ignore=file ¶

Before dumping a directory, tar checks if it contains file. If so, exclusion patterns are read from this file. The patterns affect only the directory itself. See Excluding Some Files.

--exclude-ignore-recursive=file ¶

Before dumping a directory, tar checks if it contains file. If so, exclusion patterns are read from this file. The patterns affect the directory and all itssubdirectories. See Excluding Some Files.

--exclude-tag=file ¶

Exclude from dump any directory containing file named file, but dump the directory node and file itself. See exclude-tag.

--exclude-tag-under=file ¶

Exclude from dump the contents of any directory containing file named file, but dump the directory node itself. See exclude-tag-under.

--exclude-tag-all=file ¶

Exclude from dump any directory containing file named file. See exclude-tag-all.

--exclude-vcs ¶

Exclude from dump directories and files, that are internal for some widely used version control systems.

See exclude-vcs.

--exclude-vcs-ignores ¶

Exclude files that match patterns read from VCS-specific ignore files. Supported files are: .cvsignore, .gitignore, .bzrignore, and .hgignore. The semantics of each file is the same as for the corresponding VCS, e.g. patterns read from .gitignore affect the directory and all its subdirectories. See exclude-vcs-ignores.

--file=archive ¶

-f archive

tar will use the file archive as the tar archive it performs operations on, rather than tar’s compilation dependent default. See The --file Option.

--files-from=file ¶

-T file

tar will use the contents of file as a list of archive members or files to operate on, in addition to those specified on the command-line. See Reading Names from a File.

--force-local ¶

Forces tar to interpret the file name given to --file as a local file, even if it looks like a remote tape drive name. See local and remote archives.

--format=format ¶

-H format

Selects output archive format. Format may be one of the following:

‘v7’

Creates an archive that is compatible with Unix V7 tar.

‘oldgnu’

Creates an archive that is compatible with GNU tar version 1.12 or earlier.

‘gnu’

Creates archive in GNU tar 1.13 format. Basically it is the same as ‘oldgnu’ with the only difference in the way it handles long numeric fields.

‘ustar’

Creates a POSIX.1-1988 compatible archive.

‘posix’

Creates a POSIX.1-2001 archive.

See Controlling the Archive Format, for a detailed discussion of these formats.

--full-time ¶

This option instructs tar to print file times to their full resolution. Usually this means 1-second resolution, but that depends on the underlying file system. The --full-time option takes effect only when detailed output (verbosity level 2 or higher) has been requested using the --verbose option, e.g., when listing or extracting archives:

$ tar -t -v --full-time -f archive.tar

or, when creating an archive:

$ tar -c -vv --full-time -f archive.tar .

Notice, thar when creating the archive you need to specify --verbose twice to get a detailed output (see The --verbose Option).

--group=group ¶

Files added to the tar archive will have a group ID of group, rather than the group from the source file. group can specify a symbolic name, or a numeric ID, or both as name:id. See Overriding File Metadata.

Also see the --group-map option and comments for the --owner=user option.

--group-map=file ¶

Read owner group translation map from file. This option allows to translate only certain group names and/or UIDs. See Overriding File Metadata, for a detailed description. When used together with --group option, the latter affects only those files whose owner group is not listed in the file.

This option does not affect extraction from archives.

--gzip ¶

--gunzip

--ungzip

-z

This option tells tar to read or write archives through gzip, allowing tar to directly operate on several kinds of compressed archives transparently. See Creating and Reading Compressed Archives.

--hard-dereference ¶

When creating an archive, dereference hard links and store the files they refer to, instead of creating usual hard link members.

See Hard Links.

--help ¶

-?

tar will print out a short message summarizing the operations and options to tar and exit. See GNU tar documentation.

--hole-detection=method ¶

Use method to detect holes in sparse files. This option implies --sparse. Valid methods are ‘seek’ and ‘raw’. Default is ‘seek’ with fallback to ‘raw’ when not applicable. See Archiving Sparse Files.

--ignore-case ¶

Ignore case when matching member or file names with patterns. See Controlling Pattern-Matching.

--ignore-command-error ¶

Ignore exit codes of subprocesses. See Writing to an External Program.

--ignore-failed-read ¶

Do not exit unsuccessfully merely because reading failed. See Ignore Failed Read.

--ignore-zeros ¶

-i

With this option, tar will ignore zeroed blocks in the archive, which normally signals EOF. This option also suppresses warnings about missing or incomplete zero blocks at the end of the archive. See Ignoring Blocks of Zeros.

--incremental ¶

-G

Informs tar that it is working with an old GNU-format incremental backup archive. It is intended primarily for backwards compatibility only. See Using tar to Perform Incremental Dumps, for a detailed discussion of incremental archives.

--index-file=file ¶

Send verbose output to file instead of to standard output.

--info-script=command ¶

--new-volume-script=command

-F command

When tar is performing multi-tape backups, command is run at the end of each tape. If it exits with nonzero status, tar fails immediately. See info-script, for a detailed discussion of this feature.

--interactive ¶

--confirmation

-w

Specifies that tar should ask the user for confirmation before performing potentially destructive options, such as overwriting files. See Asking for Confirmation During Operations.

--keep-directory-symlink ¶

This option changes the behavior of tar when it encounters a symlink with the same name as the directory that it is about to extract. By default, in this case tar would first remove the symlink and then proceed extracting the directory.

The --keep-directory-symlink option disables this behavior and instructs tar to follow symlinks to directories when extracting from the archive.

It is mainly intended to provide compatibility with the Slackware installation scripts.

--keep-newer-files ¶

Do not replace existing files that are newer than their archive copies when extracting files from an archive.

--keep-old-files ¶

-k

Do not overwrite existing files when extracting files from an archive. Return error if such files exist. See also --skip-old-files.

See Keep Old Files.

--label=name ¶

-V name

When creating an archive, instructs tar to write name as a name record in the archive. When extracting or listing archives, tar will only operate on archives that have a label matching the pattern specified in name. See Tape Files.

--level=n ¶

Force incremental backup of level n. As of GNU tar version 1.35, the option --level=0 truncates the snapshot file, thereby forcing the level 0 dump. Other values of n are effectively ignored. See --level=0, for details and examples.

The use of this option is valid only in conjunction with the --listed-incremental option. See Using tar to Perform Incremental Dumps, for a detailed description.

--listed-incremental=snapshot-file ¶

-g snapshot-file

During a --create operation, specifies that the archive that tar creates is a new GNU-format incremental backup, using snapshot-file to determine which files to backup. With other operations, informs tar that the archive is in incremental format. See Using tar to Perform Incremental Dumps.

--lzip ¶

This option tells tar to read or write archives through lzip. See Creating and Reading Compressed Archives.

--lzma ¶

This option tells tar to read or write archives through lzma. See Creating and Reading Compressed Archives.

--lzop

This option tells tar to read or write archives through lzop. See Creating and Reading Compressed Archives.

--mode=permissions ¶

When adding files to an archive, tar will use permissions for the archive members, rather than the permissions from the files. permissions can be specified either as an octal number or as symbolic permissions, like with chmod. See Overriding File Metadata.

--mtime=date ¶

When adding files to an archive, tar will use date as the modification time of members when creating archives, instead of their actual modification times. The value of date can be either a textual date representation (see Date input formats) or a name of the existing file, starting with ‘/’ or ‘.’. In the latter case, the modification time of that file is used. See Overriding File Metadata.

When --clamp-mtime is also specified, files with modification times earlier than date will retain their actual modification times, and date will only be used for files whose modification times are later than date.

--multi-volume ¶

-M

Informs tar that it should create or otherwise operate on a multi-volume tar archive. See Using Multiple Tapes.

--new-volume-script ¶

(see --info-script)

--newer=date ¶

--after-date=date

-N

When creating an archive, tar will only add files that have changed since date. If date begins with ‘/’ or ‘.’, it is taken to be the name of a file whose data modification time specifies the date. See Operating Only on New Files.

--newer-mtime=date ¶

Like --newer, but add only files whose contents have changed (as opposed to just --newer, which will also back up files for which any status information has changed). See Operating Only on New Files.

--no-acls ¶

Disable the POSIX ACLs support. See acls.

--no-anchored ¶

An exclude pattern can match any subsequence of the name’s components. See Controlling Pattern-Matching.

--no-auto-compress ¶

Disables automatic compressed format recognition based on the archive suffix. See --auto-compress. See Creating and Reading Compressed Archives.

--no-check-device ¶

Do not check device numbers when creating a list of modified files for incremental archiving. See device numbers, for a detailed description.

--no-delay-directory-restore ¶

Modification times and permissions of extracted directories are set when all files from this directory have been extracted. This is the default. See Directory Modification Times and Permissions.

--no-ignore-case ¶

Use case-sensitive matching. See Controlling Pattern-Matching.

--no-ignore-command-error ¶

Print warnings about subprocesses that terminated with a nonzero exit code. See Writing to an External Program.

--no-null ¶

If the --null option was given previously, this option cancels its effect, so that any following --files-from options will expect their file lists to be newline-terminated.

--no-overwrite-dir ¶

Preserve metadata of existing directories when extracting files from an archive. See Overwrite Old Files.

--no-quote-chars=string ¶

Remove characters listed in string from the list of quoted characters set by the previous --quote-chars option (see Quoting Member Names).

--no-recursion ¶

With this option, tar will not recurse into directories. See Descending into Directories.

--no-same-owner ¶

-o

When extracting an archive, do not attempt to preserve the owner specified in the tar archive. This the default behavior for ordinary users.

--no-same-permissions ¶

When extracting an archive, subtract the user’s umask from files from the permissions specified in the archive. This is the default behavior for ordinary users.

--no-seek ¶

The archive media does not support seeks to arbitrary locations. Usually tar determines automatically whether the archive can be seeked or not. Use this option to disable this mechanism.

--no-selinux ¶

Disable SELinux context support. See SELinux.

--no-unquote ¶

Treat all input file or member names literally, do not interpret escape sequences. See input name quoting.

--no-verbatim-files-from ¶

Instructs GNU tar to treat each line read from a file list as if it were supplied in the command line. I.e., leading and trailing whitespace is removed and, if the result begins with a dash, it is treated as a GNU tar command line option.

This is default behavior. This option is provided as a way to restore it after --verbatim-files-from option.

It is implied by the --no-null option.

See no-verbatim-files-from.

--no-wildcards ¶

Do not use wildcards. See Controlling Pattern-Matching.

--no-wildcards-match-slash ¶

Wildcards do not match ‘/’. See Controlling Pattern-Matching.

--no-xattrs ¶

Disable extended attributes support. See xattrs.

--null ¶

When tar is using the --files-from option, this option instructs tar to expect file names terminated with NUL, and to process file names verbatim.

This means that tar correctly works with file names that contain newlines or begin with a dash.

See NUL-Terminated File Names.

See also verbatim-files-from.

--numeric-owner ¶

This option will notify tar that it should use numeric user and group IDs when creating a tar file, rather than names. See Handling File Attributes.

-o

The function of this option depends on the action tar is performing. When extracting files, -o is a synonym for --no-same-owner, i.e., it prevents tar from restoring ownership of files being extracted.

When creating an archive, it is a synonym for --old-archive. This behavior is for compatibility with previous versions of GNU tar, and will be removed in future releases.

See Changes, for more information.

--occurrence[=number] ¶

This option can be used in conjunction with one of the subcommands --delete, --diff, --extract or --list when a list of files is given either on the command line or via -T option.

This option instructs tar to process only the numberth occurrence of each named file. Number defaults to 1, so

tar -x -f archive.tar --occurrence filename

will extract the first occurrence of the member filename from archive.tar and will terminate without scanning to the end of the archive.

--old-archive ¶

Synonym for --format=v7.

--one-file-system ¶

Used when creating an archive. Prevents tar from recursing into directories that are on different file systems from the current directory.

--one-top-level[=dir] ¶

Tells tar to create a new directory beneath the extraction directory (or the one passed to -C) and use it to guard against tarbombs. In the absence of dir argument, the name of the new directory will be equal to the base name of the archive (file name minus the archive suffix, if recognized). Any member names that do not begin with that directory name (after transformations from --transform and --strip-components) will be prefixed with it. Recognized file name suffixes are ‘.tar’, and any compression suffixes recognizable by See --auto-compress.

--overwrite ¶

Overwrite existing files and directory metadata when extracting files from an archive. See Overwrite Old Files.

--overwrite-dir ¶

Overwrite the metadata of existing directories when extracting files from an archive. See Overwrite Old Files.

--owner=user ¶

Specifies that tar should use user as the owner of members when creating archives, instead of the user associated with the source file. user can specify a symbolic name, or a numeric ID, or both as name:id. See Overriding File Metadata.

This option does not affect extraction from archives. See also --owner-map, below.

--owner-map=file ¶

Read owner translation map from file. This option allows to translate only certain owner names or UIDs. See Overriding File Metadata, for a detailed description. When used together with --owner option, the latter affects only those files whose owner is not listed in the file.

This option does not affect extraction from archives.

--pax-option=keyword-list ¶

This option enables creation of the archive in POSIX.1-2001 format (see GNU tar and POSIX tar) and modifies the way tar handles the extended header keywords. Keyword-list is a comma-separated list of keyword options. See Controlling Extended Header Keywords, for a detailed discussion.

--portability ¶

--old-archive

Synonym for --format=v7.

--posix ¶

Same as --format=posix.

--preserve-order ¶

(See --same-order; see Same Order.)

--preserve-permissions ¶

--same-permissions

-p

When tar is extracting an archive, it normally subtracts the users’ umask from the permissions specified in the archive and uses that number as the permissions to create the destination file. Specifying this option instructs tar that it should use the permissions directly from the archive. See Setting Access Permissions.

--quote-chars=string ¶

Always quote characters from string, even if the selected quoting style would not quote them (see Quoting Member Names).

--quoting-style=style ¶

Set quoting style to use when printing member and file names (see Quoting Member Names). Valid style values are: literal, shell, shell-always, c, escape, locale, and clocale. Default quoting style is escape, unless overridden while configuring the package.

--read-full-records ¶

-B

Specifies that tar should reblock its input, for reading from pipes on systems with buggy implementations. See Options to Help Read Archives.

--record-size=size[suf] ¶

Instructs tar to use size bytes per record when accessing the archive. The argument can be suffixed with a size suffix, e.g. --record-size=10K for 10 Kilobytes. See Table 9.1, for a list of valid suffixes. See The Blocking Factor of an Archive, for a detailed description of this option.

--recursion ¶

With this option, tar recurses into directories (default). See Descending into Directories.

--recursive-unlink ¶

Remove existing directory hierarchies before extracting directories of the same name from the archive. See Recursive Unlink.

--remove-files ¶

Directs tar to remove the source file from the file system after appending it to an archive. See Removing Files.

--restrict ¶

Disable use of some potentially harmful tar options. Currently this option disables shell invocation from multi-volume menu (see Using Multiple Tapes).

--rmt-command=cmd ¶

Notifies tar that it should use cmd instead of the default /usr/libexec/rmt (see Remote Tape Server).

--rsh-command=cmd ¶

Notifies tar that is should use cmd to communicate with remote devices. See Device Selection and Switching.

--same-order ¶

--preserve-order

-s

This option is an optimization for tar when running on machines with small amounts of memory. It informs tar that the list of file arguments has already been sorted to match the order of files in the archive. See Same Order.

--same-owner ¶

When extracting an archive, tar will attempt to preserve the owner specified in the tar archive with this option present. This is the default behavior for the superuser; this option has an effect only for ordinary users. See Handling File Attributes.

--same-permissions ¶

(See --preserve-permissions; see Setting Access Permissions.)

--seek ¶

-n

Assume that the archive media supports seeks to arbitrary locations. Usually tar determines automatically whether the archive can be seeked or not. This option is intended for use in cases when such recognition fails. It takes effect only if the archive is open for reading (e.g. with --list or --extract options).

--selinux ¶

Enable the SELinux context support. See selinux.

--show-defaults ¶

Displays the default options used by tar and exits successfully. This option is intended for use in shell scripts. Here is an example of what you can see using this option:

$ tar --show-defaults
--format=gnu -f- -b20 --quoting-style=escape
--rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh

Notice, that this option outputs only one line. The example output above has been split to fit page boundaries. See Obtaining GNU tar default values.

--show-omitted-dirs ¶

Instructs tar to mention the directories it is skipping when operating on a tar archive. See show-omitted-dirs.

--show-snapshot-field-ranges ¶

Displays the range of values allowed by this version of tar for each field in the snapshot file, then exits successfully. See Format of the Incremental Snapshot Files.

--show-transformed-names ¶

--show-stored-names

Display file or member names after applying any transformations (see Modifying File and Member Names). In particular, when used in conjunction with one of the archive creation operations it instructs tar to list the member names stored in the archive, as opposed to the actual file names. See listing member and file names.

--skip-old-files ¶

Do not overwrite existing files when extracting files from an archive. See Keep Old Files.

This option differs from --keep-old-files in that it does not treat such files as an error, instead it just silently avoids overwriting them.

The --warning=existing-file option can be used together with this option to produce warning messages about existing old files (see Controlling Warning Messages).

--sort=order ¶

Specify the directory sorting order when reading directories. Order may be one of the following:

‘none’

No directory sorting is performed. This is the default.

‘name’

Sort the directory entries on name. The operating system may deliver directory entries in a more or less random order, and sorting them makes archive creation reproducible.

‘inode’

Sort the directory entries on inode number. Sorting directories on inode number may reduce the amount of disk seek operations when creating an archive for some file systems.

--sparse ¶

-S

Invokes a GNU extension when adding files to an archive that handles sparse files efficiently. See Archiving Sparse Files.

--sparse-version=version ¶

Specifies the format version to use when archiving sparse files. Implies --sparse. See Archiving Sparse Files. For the description of the supported sparse formats, See Storing Sparse Files.

--starting-file=name ¶

-K name

This option affects extraction only; tar will skip extracting files in the archive until it finds one that matches name. See Coping with Scarce Resources.

--strip-components=number ¶

Strip given number of leading components from file names before extraction. For example, if archive archive.tar contained /some/file/name, then running

tar --extract --file archive.tar --strip-components=2

would extract this file to file name.

See Modifying File and Member Names.

--suffix=suffix ¶

Alters the suffix tar uses when backing up files from the default ‘~’. See Backup options.

--tape-length=num[suf] ¶

-L num[suf]

Specifies the length of tapes that tar is writing as being num x 1024 bytes long. If optional suf is given, it specifies a multiplicative factor to be used instead of 1024. For example, ‘-L2M’ means 2 megabytes. See Table 9.1, for a list of allowed suffixes. See Using Multiple Tapes, for a detailed discussion of this option.

--test-label ¶

Reads the volume label. If an argument is specified, test whether it matches the volume label. See --test-label option.

--to-command=command ¶

During extraction tar will pipe extracted files to the standard input of command. See Writing to an External Program.

--to-stdout ¶

-O

During extraction, tar will extract files to stdout rather than to the file system. See Writing to Standard Output.

--totals[=signo] ¶

Displays the total number of bytes transferred when processing an archive. If an argument is given, these data are displayed on request, when signal signo is delivered to tar. See totals.

--touch ¶

-m

Sets the data modification time of extracted files to the extraction time, rather than the data modification time stored in the archive. See Setting Data Modification Times.

--transform=sed-expr ¶

--xform=sed-expr

Transform file or member names using sed replacement expression sed-expr. For example,

$ tar cf archive.tar --transform 's,^\./,usr/,' .

will add to archive files from the current working directory, replacing initial ‘./’ prefix with ‘usr/’. For the detailed discussion, See Modifying File and Member Names.

To see transformed member names in verbose listings, use --show-transformed-names option (see show-transformed-names).

--uncompress ¶

(See --compress, see Creating and Reading Compressed Archives)

--ungzip ¶

(See --gzip, see Creating and Reading Compressed Archives)

--unlink-first ¶

-U

Directs tar to remove the corresponding file from the file system before extracting it from the archive. See Unlink First.

--unquote ¶

Enable unquoting input file or member names (default). See input name quoting.

--use-compress-program=prog ¶

-I=prog

Instructs tar to access the archive through prog, which is presumed to be a compression program of some sort. See Creating and Reading Compressed Archives.

--utc ¶

Display file modification dates in UTC. This option implies --verbose.

--verbatim-files-from ¶

Instructs GNU tar to treat each line read from a file list as a file name, even if it starts with a dash.

File lists are supplied with the --files-from (-T) option. By default, each line read from a file list is first trimmed off the leading and trailing whitespace and, if the result begins with a dash, it is treated as a GNU tar command line option.

Use the --verbatim-files-from option to disable this special handling. This facilitates the use of tar with file lists created by file command.

This option affects all --files-from options that occur after it in the command line. Its effect is reverted by the --no-verbatim-files-from option.

This option is implied by the --null option.

See verbatim-files-from.

--verbose ¶

-v

Specifies that tar should be more verbose about the operations it is performing. This option can be specified multiple times for some operations to increase the amount of information displayed. See Checking tar progress.

--verify ¶

-W

Verifies that the archive was correctly written when creating an archive. See Verifying Data as It is Stored.

--version ¶

Print information about the program’s name, version, origin and legal status, all on standard output, and then exit successfully. See GNU tar documentation.

--volno-file=file ¶

Used in conjunction with --multi-volume. tar will keep track of which volume of a multi-volume archive it is working in file. See volno-file.

--warning=keyword ¶

Enable or disable warning messages identified by keyword. The messages are suppressed if keyword is prefixed with ‘no-’. See Controlling Warning Messages.

--wildcards ¶

Use wildcards when matching member names with patterns. See Controlling Pattern-Matching.

--wildcards-match-slash ¶

Wildcards match ‘/’. See Controlling Pattern-Matching.

--xattrs ¶

Enable extended attributes support. See xattrs.

--xattrs-exclude=pattern ¶

Specify exclude pattern for xattr keys. See xattrs-exclude.

--xattrs-include=pattern. ¶

Specify include pattern for xattr keys. pattern is a globbing pattern, e.g. ‘--xattrs-include='user.*'’ to include only attributes from the user namespace. See xattrs-include.

--xz ¶

-J

Use xz for compressing or decompressing the archives. See Creating and Reading Compressed Archives.

--zstd

Use zstd for compressing or decompressing the archives. See Creating and Reading Compressed Archives.

3.4.3 Short Options Cross Reference ¶

Here is an alphabetized list of all of the short option forms, matching them with the equivalent long option.

3.4.4 Position-Sensitive Options ¶

Some GNU tar options can be used multiple times in the same invocation and affect all arguments that appear after them. These are options that control how file names are selected and what kind of pattern matching is used.

The most obvious example is the -C option. It instructs tar to change to the directory given as its argument prior to processing the rest of command line (see Changing the Working Directory). Thus, in the following command:

tar -c -f a.tar -C /etc passwd -C /var log spool

the file passwd will be searched in the directory /etc, and files log and spool – in /var.

These options can also be used in a file list supplied with the --files-from (-T) option (see Reading Names from a File). In that case they affect all files (patterns) appearing in that file after them and remain in effect for any arguments processed after that file. For example, if the file list.txt contained:

README
-C src
main.c

and tar were invoked as follows:

tar -c -f a.tar -T list.txt Makefile

then the file README would be looked up in the current working directory, and files main.c and Makefile would be looked up in the directory src.

Many options can be prefixed with --no- to cancel the effect of the original option.

For example, the --recursion option controls whether to recurse in the subdirectories. It’s counterpart --no-recursion disables this. Consider the command below. It will store in the archive the directory /usr with all files and directories that are located in it as well as any files and directories in /var, without recursing into them⁶:

tar -cf a.tar --recursion /usr --no-recursion /var/*

During archive creation, GNU tar keeps track of positional options used and arguments affected by them. If it finds out that any such options are used in an obviously erroneous way, the fact is reported and exit code is set to 2. E.g.:

$ tar -cf a.tar . --exclude '*.o'
tar: The following options were used after any non-optional
arguments in archive create or update mode.  These options are
positional and affect only arguments that follow them.  Please,
rearrange them properly.
tar: --exclude '*.o' has no effect
tar: Exiting with failure status due to previous errors

The following table summarizes all position-sensitive options.

--directory=dir

-C dir

See Changing the Working Directory.

--null

--no-null

See NUL-Terminated File Names.

--unquote

--no-unquote

See input name quoting.

--verbatim-files-from

--no-verbatim-files-from

See verbatim-files-from.

--recursion

--no-recursion

See Descending into Directories.

--anchored

--no-anchored

See anchored patterns.

--ignore-case

--no-ignore-case

See case-insensitive matches.

--wildcards

--no-wildcards

See Controlling Pattern-Matching.

--wildcards-match-slash

--no-wildcards-match-slash

See Controlling Pattern-Matching.

--exclude

See Excluding Some Files.

--exclude-from

-X

--exclude-caches

--exclude-caches-under

--exclude-caches-all

--exclude-tag

--exclude-ignore

--exclude-ignore-recursive

--exclude-tag-under

--exclude-tag-all

--exclude-vcs

--exclude-vcs-ignores

--exclude-backups

See Excluding Some Files.

3.9.1 Keywords controlling tar operation ¶

These keywords control warnings that may appear in any GNU tar operation mode:

warning: filename-with-nuls ¶

‘file name read contains nul character’

warning: filename-with-nuls ¶

‘%s: file name read contains nul character’

warning: alone-zero-block ¶

‘A lone zero block at %s’. Notice, that this warning is suppressed if --ignore-zeros is in effect (see Ignoring Blocks of Zeros).

warning: missing-zero-blocks ¶

‘Terminating zero blocks missing at %s’. This warning is suppressed if --ignore-zeros is in effect (see Ignoring Blocks of Zeros).

3.9.2 Keywords applicable for tar --create ¶

The following keywords control messages that can be issued while creating archives.

warning: cachedir ¶

‘%s: contains a cache directory tag %s; %s’

warning: file-shrank ¶

‘%s: File shrank by %s bytes; padding with zeros’

warning: xdev ¶

‘%s: file is on a different filesystem; not dumped’

warning: file-ignored ¶

‘%s: Unknown file type; file ignored’
‘%s: socket ignored’
‘%s: door ignored’

warning: file-unchanged ¶

‘%s: file is unchanged; not dumped’

warning: ignore-archive ¶

‘%s: archive cannot contain itself; not dumped’

warning: file-removed ¶

‘%s: File removed before we read it’

warning: file-changed ¶

‘%s: file changed as we read it’

Suppresses warnings about read failures, which can occur if files or directories are unreadable, or if they change while being read. This keyword applies only if used together with the --ignore-failed-read option. See Ignore Failed Read.

3.9.3 Keywords applicable for tar --extract ¶

The following keywords control warnings that can be issued during archive extraction.

warning: existing-file ¶

‘%s: skipping existing file’

warning: timestamp ¶

‘%s: implausibly old time stamp %s’
‘%s: time stamp %s is %s s in the future’

warning: contiguous-cast ¶

‘Extracting contiguous files as regular files’

warning: symlink-cast ¶

‘Attempting extraction of symbolic links as hard links’, warning message ‘Attempting extraction of symbolic links as hard links’

warning: unknown-cast ¶

‘%s: Unknown file type '%c', extracted as normal file’

warning: ignore-newer ¶

‘Current %s is newer or same age’

warning: unknown-keyword ¶

‘Ignoring unknown extended header keyword '%s'’

warning: decompress-program ¶

Controls verbose description of failures occurring when trying to run alternative decompressor programs (see alternative decompression programs). This warning is disabled by default (unless --verbose is used). A common example of what you can get when using this warning is:

$ tar --warning=decompress-program -x -f archive.Z
tar (child): cannot run compress: No such file or directory
tar (child): trying gzip

This means that tar first tried to decompress archive.Z using compress, and, when that failed, switched to gzip.

warning: record-size ¶

‘Record size = %lu blocks’

3.9.4 Keywords controlling incremental extraction ¶

These keywords control warnings that may appear when extracting from incremental archives.

warning: rename-directory ¶

‘%s: Directory has been renamed from %s’
‘%s: Directory has been renamed’

warning: new-directory ¶

‘%s: Directory is new’

warning: xdev ¶

‘%s: directory is on a different device: not purging’

warning: bad-dumpdir ¶

‘Malformed dumpdir: 'X' never used’

3.9.5 Warning Classes ¶

These convenience keywords define warning classes. When used, they affect several warnings at once.

warning: all ¶

Enable all warning messages.

warning: none ¶

Disable all warning messages.

warning: verbose ¶

A shorthand for all messages enabled when --verbose (see The --verbose Option) is in effect. These are: decompress-program, existing-file, new-directory, record-size, rename-directory.

3.9.6 Default Warning Settings ¶

GNU tar default settings correspond to:

--warning=all --warning=no-verbose --warning=no-missing-zero-blocks

4.2.1 The Five Advanced tar Operations ¶

In the last chapter, you learned about the first three operations to tar. This chapter presents the remaining five operations to tar: --append, --update, --concatenate, --delete, and --compare.

You are not likely to use these operations as frequently as those covered in the last chapter; however, since they perform specialized functions, they are quite useful when you do need to use them. We will give examples using the same directory and files that you created in the last chapter. As you may recall, the directory is called practice, the files are ‘jazz’, ‘blues’, ‘folk’, and the two archive files you created are ‘collection.tar’ and ‘music.tar’.

We will also use the archive files ‘afiles.tar’ and ‘bfiles.tar’. The archive ‘afiles.tar’ contains the members ‘apple’, ‘angst’, and ‘aspic’; ‘bfiles.tar’ contains the members ‘./birds’, ‘baboon’, and ‘./box’.

Unless we state otherwise, all practicing you do and examples you follow in this chapter will take place in the practice directory that you created in the previous chapter; see Preparing a Practice Directory for Examples. (Below in this section, we will remind you of the state of the examples where the last chapter left them.)

The five operations that we will cover in this chapter are:

--append

-r

Add new entries to an archive that already exists.

--update

-u

Add more recent copies of archive members to the end of an archive, if they exist.

--concatenate

--catenate

-A

Add one or more pre-existing archives to the end of another archive.

--delete

Delete items from an archive (does not work on tapes).

--compare

--diff

-d

Compare archive members to their counterparts in the file system.

4.2.2 How to Add Files to Existing Archives: --append ¶

If you want to add files to an existing archive, you don’t need to create a new archive; you can use --append (-r). The archive must already exist in order to use --append. (A related operation is the --update operation; you can use this to add newer versions of archive members to an existing archive. To learn how to do this with --update, see Updating an Archive.)

If you use --append to add a file that has the same name as an archive member to an archive containing that archive member, then the old member is not deleted. What does happen, however, is somewhat complex. tar allows you to have infinite number of files with the same name. Some operations treat these same-named members no differently than any other set of archive members: for example, if you view an archive with --list (-t), you will see all of those members listed, with their data modification times, owners, etc.

Other operations don’t deal with these members as perfectly as you might prefer; if you were to use --extract to extract the archive, only the most recently added copy of a member with the same name as other members would end up in the working directory. This is because --extract extracts an archive in the order the members appeared in the archive; the most recently archived members will be extracted last. Additionally, an extracted member will replace a file of the same name which existed in the directory already, and tar will not prompt you about this¹⁰. Thus, only the most recently archived member will end up being extracted, as it will replace the one extracted before it, and so on.

There exists a special option that allows you to get around this behavior and extract (or list) only a particular copy of the file. This is --occurrence option. If you run tar with this option, it will extract only the first copy of the file. You may also give this option an argument specifying the number of copy to be extracted. Thus, for example if the archive archive.tar contained three copies of file myfile, then the command

tar --extract --file archive.tar --occurrence=2 myfile

would extract only the second copy. See —occurrence, for the description of --occurrence option.

If you want to replace an archive member, use --delete to delete the member you want to remove from the archive, and then use --append to add the member you want to be in the archive. Note that you can not change the order of the archive; the most recently added member will still appear last. In this sense, you cannot truly “replace” one member with another. (Replacing one member with another will not work on certain types of media, such as tapes; see Removing Archive Members Using --delete and Tapes and Other Archive Media, for more information.)

• Appending Files to an Archive
• Multiple Members with the Same Name

$ tar --append --file=collection.tar rock

$ 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

$ tar --append --verbose --file=collection.tar blues
blues

$ 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

$ tar --extract -vv --occurrence --file=collection.tar blues
-rw-r--r-- me/user          21 1996-09-23 16:44 blues

4.2.3 Updating an Archive ¶

In the previous section, you learned how to use --append to add a file to an existing archive. A related operation is --update (-u). The --update operation updates a tar archive by comparing the date of the specified archive members against the date of the file with the same name. If the file has been modified more recently than the archive member, then the newer version of the file is added to the archive (as with --append).

Unfortunately, you cannot use --update with magnetic tape drives. The operation will fail.

Both --update and --append work by adding to the end of the archive. When you extract a file from the archive, only the version stored last will wind up in the file system, unless you use the --backup option. See Multiple Members with the Same Name, for a detailed discussion.

• How to Update an Archive Using --update

$ tar --update -v -f collection.tar blues folk rock classical
blues
classical
$

4.2.4 Combining Archives with --concatenate ¶

Sometimes it may be convenient to add a second archive onto the end of an archive rather than adding individual files to the archive. To add one or more archives to the end of another archive, you should use the --concatenate (--catenate, -A) operation.

To use --concatenate, give the first archive with --file option and name the rest of archives to be concatenated on the command line. The members, and their member names, will be copied verbatim from those archives to the first one¹¹. The new, concatenated archive will be called by the same name as the one given with the --file option. As usual, if you omit --file, tar will use the value of the environment variable TAPE, or, if this has not been set, the default archive name.

To demonstrate how --concatenate works, create two small archives called bluesrock.tar and folkjazz.tar, using the relevant files from practice:

$ tar -cvf bluesrock.tar blues rock
blues
rock
$ tar -cvf folkjazz.tar folk jazz
folk
jazz

If you like, you can run ‘tar --list’ to make sure the archives contain what they are supposed to:

$ 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
$ 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

We can concatenate these two archives with tar:

$ tar --concatenate --file=bluesrock.tar jazzfolk.tar

If you now list the contents of the bluesrock.tar, you will see that now it also contains the archive members of jazzfolk.tar:

$ tar --list --file=bluesrock.tar
blues
rock
folk
jazz

When you use --concatenate, the source and target archives must already exist and must have been created using compatible format parameters. Notice, that tar does not check whether the archives it concatenates have compatible formats, it does not even check if the files are really tar archives.

Like --append (-r), this operation cannot be performed on some tape drives, due to deficiencies in the formats those tape drives use.

It may seem more intuitive to you to want or try to use cat to concatenate two archives instead of using the --concatenate operation; after all, cat is the utility for combining files.

However, tar archives incorporate an end-of-file marker which must be removed if the concatenated archives are to be read properly as one archive. --concatenate removes the end-of-archive marker from the target archive before each new archive is appended. If you use cat to combine the archives, the result will not be a valid tar format archive. If you need to retrieve files from an archive that was added to using the cat utility, use the --ignore-zeros (-i) option. See Ignoring Blocks of Zeros, for further information on dealing with archives improperly combined using the cat shell utility.

4.2.5 Removing Archive Members Using --delete ¶

You can remove members from an archive by using the --delete option. Specify the name of the archive with --file (-f) and then specify the names of the members to be deleted; if you list no member names, nothing will be deleted. The --verbose option will cause tar to print the names of the members as they are deleted. As with --extract, you must give the exact member names when using ‘tar --delete’. --delete will remove all versions of the named file from the archive. The --delete operation can run very slowly.

Unlike other operations, --delete has no short form.

This operation will rewrite the archive. You can only use --delete on an archive if the archive device allows you to write to any point on the media, such as a disk; because of this, it does not work on magnetic tapes. Do not try to delete an archive member from a magnetic tape; the action will not succeed, and you will be likely to scramble the archive and damage your tape. There is no safe way (except by completely re-writing the archive) to delete files from most kinds of magnetic tape. See Tapes and Other Archive Media.

To delete all versions of the file blues from the archive collection.tar in the practice directory, make sure you are in that directory, and then,

$ tar --list --file=collection.tar
blues
folk
jazz
rock
$ tar --delete --file=collection.tar blues
$ tar --list --file=collection.tar
folk
jazz
rock

The --delete option has been reported to work properly when tar acts as a filter from stdin to stdout.

4.2.6 Comparing Archive Members with the File System ¶

The --compare (-d), or --diff operation compares specified archive members against files with the same names, and then reports differences in file size, mode, owner, modification date and contents. You should only specify archive member names, not file names. If you do not name any members, then tar will compare the entire archive. If a file is represented in the archive but does not exist in the file system, tar reports a difference.

You have to specify the record size of the archive when modifying an archive with a non-default record size.

tar ignores files in the file system that do not have corresponding members in the archive.

The following example compares the archive members rock, blues and funk in the archive bluesrock.tar with files of the same name in the file system. (Note that there is no file, funk; tar will report an error message.)

$ tar --compare --file=bluesrock.tar rock blues funk
rock
blues
tar: funk not found in archive

The spirit behind the --compare (--diff, -d) option is to check whether the archive represents the current state of files on disk, more than validating the integrity of the archive media. For this latter goal, see Verifying Data as It is Stored.

4.3.1 Overriding File Metadata ¶

As described above, a tar archive keeps, for each member it contains, its metadata, such as modification time, mode and ownership of the file. GNU tar allows to replace these data with other values when adding files to the archive. The options described in this section affect creation of archives of any type. For POSIX archives, see also Controlling Extended Header Keywords, for additional ways of controlling metadata, stored in the archive.

--mode=permissions ¶

When adding files to an archive, tar will use permissions for the archive members, rather than the permissions from the files. permissions can be specified either as an octal number or as symbolic permissions, like with chmod (See File permissions in GNU file utilities. This reference also has useful information for those not being overly familiar with the UNIX permission system). Using latter syntax allows for more flexibility. For example, the value ‘a+rw’ adds read and write permissions for everybody, while retaining executable bits on directories or on any other file already marked as executable:

$ tar -c -f archive.tar --mode='a+rw' .

--mtime=date ¶

When adding files to an archive, tar will use date as the modification time of members when creating archives, instead of their actual modification times. The argument date can be either a textual date representation in almost arbitrary format (see Date input formats) or a name of an existing file, starting with ‘/’ or ‘.’. In the latter case, the modification time of that file will be used.

The following example will set the modification date to 00:00:00, January 1, 1970:

$ tar -c -f archive.tar --mtime='1970-01-01' .

When used with --verbose (see The --verbose Option) GNU tar will try to convert the specified date back to its textual representation and compare it with the one given with --mtime options. If the two dates differ, tar will print a warning saying what date it will use. This is to help user ensure he is using the right date.

For example:

$ tar -c -f archive.tar -v --mtime=yesterday .
tar: Option --mtime: Treating date 'yesterday' as 2006-06-20
13:06:29.152478
...

When used with --clamp-mtime GNU tar will only set the modification date to date on files whose actual modification date is later than date. This is to make it easy to build reproducible archives given a common timestamp for generated files while still retaining the original timestamps of untouched files.

$ tar -c -f archive.tar --clamp-mtime --mtime=@$SOURCE_DATE_EPOCH .

--owner=user ¶

Specifies that tar should use user as the owner of members when creating archives, instead of the user associated with the source file.

If user contains a colon, it is taken to be of the form name:id where a nonempty name specifies the user name and a nonempty id specifies the decimal numeric user ID. If user does not contain a colon, it is taken to be a user number if it is one or more decimal digits; otherwise it is taken to be a user name.

If a name is given but no number, the number is inferred from the current host’s user database if possible, and the file’s user number is used otherwise. If a number is given but no name, the name is inferred from the number if possible, and an empty name is used otherwise. If both name and number are given, the user database is not consulted, and the name and number need not be valid on the current host.

There is no value indicating a missing number, and ‘0’ usually means root. Some people like to force ‘0’ as the value to offer in their distributions for the owner of files, because the root user is anonymous anyway, so that might as well be the owner of anonymous archives. For example:

$ tar -c -f archive.tar --owner=0 .

or:

$ tar -c -f archive.tar --owner=root .

--group=group ¶

Files added to the tar archive will have a group ID of group, rather than the group from the source file. As with --owner, the argument group can be an existing group symbolic name, or a decimal numeric group ID, or name:id.

The --owner and --group options affect all files added to the archive. GNU tar provides also two options that allow for more detailed control over owner translation:

--owner-map=file

Read UID translation map from file.

When reading, empty lines are ignored. The ‘#’ sign, unless quoted, introduces a comment, which extends to the end of the line. Each nonempty line defines mapping for a single UID. It must consist of two fields separated by any amount of whitespace. The first field defines original username and UID. It can be a valid user name or a valid UID prefixed with a plus sign. In both cases the corresponding UID or user name is inferred from the current host’s user database.

The second field defines the UID and username to map the original one to. Its format can be the same as described above. Otherwise, it can have the form newname:newuid, in which case neither newname nor newuid are required to be valid as per the user database.

For example, consider the following file:

+10     bin
smith   root:0

Given this file, each input file that is owner by UID 10 will be stored in archive with owner name ‘bin’ and owner UID corresponding to ‘bin’. Each file owned by user ‘smith’ will be stored with owner name ‘root’ and owner ID 0. Other files will remain unchanged.

When used together with --owner-map, the --owner option affects only files whose owner is not listed in the map file.

--group-map=file

Read GID translation map from file.

The format of file is the same as for --owner-map option:

Each nonempty line defines mapping for a single GID. It must consist of two fields separated by any amount of whitespace. The first field defines original group name and GID. It can be a valid group name or a valid GID prefixed with a plus sign. In both cases the corresponding GID or user name is inferred from the current host’s group database.

The second field defines the GID and group name to map the original one to. Its format can be the same as described above. Otherwise, it can have the form newname:newgid, in which case neither newname nor newgid are required to be valid as per the group database.

When used together with --group-map, the --group option affects only files whose owner group is not rewritten using the map file.

4.3.2 Extended File Attributes ¶

Extended file attributes are name-value pairs that can be associated with each node in a file system. Despite the fact that POSIX.1e draft which proposed them has been withdrawn, the extended file attributes are supported by many file systems. GNU tar can store extended file attributes along with the files. This feature is controlled by the following command line arguments:

--xattrs

Enable extended attributes support. When used with --create, this option instructs GNU tar to store extended file attribute in the created archive. This implies POSIX.1-2001 archive format (--format=pax).

When used with --extract, this option tells tar, for each file extracted, to read stored attributes from the archive and to apply them to the file.

--no-xattrs

Disable extended attributes support. This is the default.

Attribute names are strings prefixed by a namespace name and a dot. Currently, four namespaces exist: ‘user’, ‘trusted’, ‘security’ and ‘system’. By default, when --xattrs is used, all names are stored in the archive (with --create), but only ‘user’ namespace is extracted (if using --extract). The reason for this behavior is that any other, system defined attributes don’t provide us sufficient compatibility promise. Storing all attributes is safe operation for the archiving purposes. Though extracting those (often security related) attributes on a different system than originally archived can lead to extraction failures, or even misinterpretations. This behavior can be controlled using the following options:

--xattrs-exclude=pattern

Specify exclude pattern for extended attributes.

--xattrs-include=pattern

Specify include pattern for extended attributes.

Here, the pattern is a globbing pattern. For example, the following command:

$ tar --xattrs --xattrs-exclude='user.*' -cf a.tar .

will include in the archive a.tar all attributes, except those from the ‘user’ namespace.

Users shall check the attributes are binary compatible with the target system before any other namespace is extracted with an explicit --xattrs-include option.

Any number of these options can be given, thereby creating lists of include and exclude patterns.

When both options are used, first --xattrs-include is applied to select the set of attribute names to keep, and then --xattrs-exclude is applied to the resulting set. In other words, only those attributes will be stored, whose names match one of the regexps in --xattrs-include and don’t match any of the regexps from --xattrs-exclude.

When listing the archive, if both --xattrs and --verbose options are given, files that have extended attributes are marked with an asterisk following their permission mask. For example:

-rw-r--r--* smith/users      110 2016-03-16 16:07 file

When two or more --verbose options are given, a detailed listing of extended attributes is printed after each file entry. Each attribute is listed on a separate line, which begins with two spaces and the letter ‘x’ indicating extended attribute. It is followed by a colon, length of the attribute and its name, e.g.:

-rw-r--r--* smith/users      110 2016-03-16 16:07 file
  x:  7 user.mime_type
  x: 32 trusted.md5sum

File access control lists (ACL) are another actively used feature proposed by the POSIX.1e standard. Each ACL consists of a set of ACL entries, each of which describes the access permissions on the file for an individual user or a group of users as a combination of read, write and search/execute permissions.

Whether or not to use ACLs is controlled by the following two options:

--acls

Enable POSIX ACLs support. When used with --create, this option instructs GNU tar to store ACLs in the created archive. This implies POSIX.1-2001 archive format (--format=pax).

When used with --extract, this option tells tar, to restore ACLs for each file extracted (provided they are present in the archive).

--no-acls

Disable POSIX ACLs support. This is the default.

When listing the archive, if both --acls and --verbose options are given, files that have ACLs are marked with a plus sign following their permission mask. For example:

-rw-r--r--+ smith/users      110 2016-03-16 16:07 file

When two or more --verbose options are given, a detailed listing of ACL is printed after each file entry:

-rw-r--r--+ smith/users      110 2016-03-16 16:07 file
  a: user::rw-,user:gray:-w-,group::r--,mask::rw-,other::r--

Security-Enhanced Linux (SELinux for short) is a Linux kernel security module that provides a mechanism for supporting access control security policies, including so-called mandatory access controls (MAC). Support for SELinux attributes is controlled by the following command line options:

--selinux

Enable the SELinux context support.

--no-selinux

Disable SELinux context support.

4.3.3 Ignore Failed Read ¶

--ignore-failed-read ¶

Do not exit with nonzero if there are mild problems while reading.

This option has effect only during creation. It instructs tar to treat as mild conditions any missing or unreadable files (directories), or files that change while reading. Such failures don’t affect the program exit code, and the corresponding diagnostic messages are marked as warnings, not errors. These warnings can be suppressed using the --warning=failed-read option (see Controlling Warning Messages).

4.4.1 Options to Help Read Archives ¶

Normally, tar will request data in full record increments from an archive storage device. If the device cannot return a full record, tar will report an error. However, some devices do not always return full records, or do not require the last record of an archive to be padded out to the next record boundary. To keep reading until you obtain a full record, or to accept an incomplete record if it contains an end-of-archive marker, specify the --read-full-records (-B) option in conjunction with the --extract or --list operations. See Blocking.

The --read-full-records (-B) option is turned on by default when tar reads an archive from standard input, or from a remote machine. This is because on BSD Unix systems, attempting to read a pipe returns however much happens to be in the pipe, even if it is less than was requested. If this option were not enabled, tar would fail as soon as it read an incomplete record from the pipe.

If you’re not sure of the blocking factor of an archive, you can read the archive by specifying --read-full-records (-B) and --blocking-factor=512-size (-b 512-size), using a blocking factor larger than what the archive uses. This lets you avoid having to determine the blocking factor of an archive. See The Blocking Factor of an Archive.

• Reading Full Records
• Ignoring Blocks of Zeros

4.4.2 Changing How tar Writes Files ¶

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• Options Controlling the Overwriting of Existing Files
• Overwrite Old Files
• Keep Old Files
• Keep Newer Files
• Unlink First
• Recursive Unlink
• Setting Data Modification Times
• Setting Access Permissions
• Directory Modification Times and Permissions
• Writing to Standard Output
• Writing to an External Program
• Removing Files

$ ls
blues
$ tar -x -k -f archive.tar
tar: blues: Cannot open: File exists
tar: Exiting with failure status due to previous errors

$ tar --no-recursion -cvf archive \
    foo foo/file1 bar bar/file foo/file2
foo/
foo/file1
bar/
bar/file
foo/file2

tar -xOzf foo.tgz bigfile | process

tar -xOzf foo.tgz bigfile1 bigfile2 | process

$ tar -x -f archive.tar \
       --to-command='proc $TAR_FILENAME $TAR_SIZE'

tar: 2345: Child returned status 1

4.4.3 Coping with Scarce Resources ¶

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• Starting File
• Same Order