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This manual is for GNU tar (version
1.22, 12 March 2009), which creates and extracts files
from archives.
Copyright © 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License".
(a) The FSF's Back-Cover Text is: “You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom.”
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GNU tar creates
and manipulates archives which are actually collections of
many other files; the program provides users with an organized and
systematic method for controlling a large amount of data.
The name “tar” originally came from the phrase “Tape ARchive”, but
archives need not (and these days, typically do not) reside on tapes.
| 1.1 What this Book Contains | ||
| 1.2 Some Definitions | ||
1.3 What tar Does | ||
1.4 How tar Archives are Named | ||
1.5 GNU tar Authors | ||
| 1.6 Reporting bugs or suggestions |
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The first part of this chapter introduces you to various terms that will
recur throughout the book. It also tells you who has worked on GNU tar
and its documentation, and where you should send bug reports
or comments.
The second chapter is a tutorial (see section Tutorial Introduction to tar) which provides a
gentle introduction for people who are new to using tar. It is
meant to be self contained, not requiring any reading from subsequent
chapters to make sense. It moves from topic to topic in a logical,
progressive order, building on information already explained.
Although the tutorial is paced and structured to allow beginners to
learn how to use tar, it is not intended solely for beginners.
The tutorial explains how to use the three most frequently used
operations (‘create’, ‘list’, and ‘extract’) as well as
two frequently used options (‘file’ and ‘verbose’). The other
chapters do not refer to the tutorial frequently; however, if a section
discusses something which is a complex variant of a basic concept, there
may be a cross reference to that basic concept. (The entire book,
including the tutorial, assumes that the reader understands some basic
concepts of using a Unix-type operating system; see section Tutorial Introduction to tar.)
The third chapter presents the remaining five operations, and
information about using tar options and option syntax.
The other chapters are meant to be used as a reference. Each chapter presents everything that needs to be said about a specific topic.
One of the chapters (see section Date input formats) exists in its
entirety in other GNU manuals, and is mostly self-contained.
In addition, one section of this manual (see section Basic Tar Format) contains a
big quote which is taken directly from tar sources.
In general, we give both long and short (abbreviated) option names at least once in each section where the relevant option is covered, so that novice readers will become familiar with both styles. (A few options have no short versions, and the relevant sections will indicate this.)
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The tar program is used to create and manipulate tar
archives. An archive is a single file which contains the contents
of many files, while still identifying the names of the files, their
owner(s), and so forth. (In addition, archives record access
permissions, user and group, size in bytes, and data modification time.
Some archives also record the file names in each archived directory, as
well as other file and directory information.) You can use tar
to create a new archive in a specified directory.
The files inside an archive are called members. Within this
manual, we use the term file to refer only to files accessible in
the normal ways (by ls, cat, and so forth), and the term
member to refer only to the members of an archive. Similarly, a
file name is the name of a file, as it resides in the file system,
and a member name is the name of an archive member within the
archive.
The term extraction refers to the process of copying an archive
member (or multiple members) into a file in the file system. Extracting
all the members of an archive is often called extracting the
archive. The term unpack can also be used to refer to the
extraction of many or all the members of an archive. Extracting an
archive does not destroy the archive's structure, just as creating an
archive does not destroy the copies of the files that exist outside of
the archive. You may also list the members in a given archive
(this is often thought of as “printing” them to the standard output,
or the command line), or append members to a pre-existing archive.
All of these operations can be performed using tar.
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tar Does The tar program provides the ability to create tar
archives, as well as various other kinds of manipulation. For example,
you can use tar on previously created archives to extract files,
to store additional files, or to update or list files which were already
stored.
Initially, tar archives were used to store files conveniently on
magnetic tape. The name tar comes from this use; it stands for
tape archiver. Despite the utility's name, tar can
direct its output to available devices, files, or other programs (using
pipes). tar may even access remote devices or files (as archives).
You can use tar archives in many ways. We want to stress a few
of them: storage, backup, and transportation.
Often, tar archives are used to store related files for
convenient file transfer over a network. For example, the
GNU Project distributes its software bundled into
tar archives, so that all the files relating to a particular
program (or set of related programs) can be transferred as a single
unit.
A magnetic tape can store several files in sequence. However, the tape
has no names for these files; it only knows their relative position on
the tape. One way to store several files on one tape and retain their
names is by creating a tar archive. Even when the basic transfer
mechanism can keep track of names, as FTP can, the nuisance of handling
multiple files, directories, and multiple links makes tar
archives useful.
Archive files are also used for long-term storage. You can think of
this as transportation from the present into the future. (It is a
science-fiction idiom that you can move through time as well as in
space; the idea here is that tar can be used to move archives in
all dimensions, even time!)
Because the archive created by tar is capable of preserving
file information and directory structure, tar is commonly
used for performing full and incremental backups of disks. A backup
puts a collection of files (possibly pertaining to many users and
projects) together on a disk or a tape. This guards against
accidental destruction of the information in those files.
GNU tar has special features that allow it to be
used to make incremental and full dumps of all the files in a
file system.
You can create an archive on one system, transfer it to another system, and extract the contents there. This allows you to transport a group of files from one system to another.
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tar Archives are Named Conventionally, tar archives are given names ending with
‘.tar’. This is not necessary for tar to operate properly,
but this manual follows that convention in order to accustom readers to
it and to make examples more clear.
Often, people refer to tar archives as “tar files,” and
archive members as “files” or “entries”. For people familiar with
the operation of tar, this causes no difficulty. However, in
this manual, we consistently refer to “archives” and “archive
members” to make learning to use tar easier for novice users.
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tar Authors GNU tar was originally written by John Gilmore,
and modified by many people. The GNU enhancements were
written by Jay Fenlason, then Joy Kendall, and the whole package has
been further maintained by Thomas Bushnell, n/BSG, François
Pinard, Paul Eggert, and finally Sergey Poznyakoff with the help of
numerous and kind users.
We wish to stress that tar is a collective work, and owes much to
all those people who reported problems, offered solutions and other
insights, or shared their thoughts and suggestions. An impressive, yet
partial list of those contributors can be found in the ‘THANKS’
file from the GNU tar distribution.
Jay Fenlason put together a draft of a GNU tar
manual, borrowing notes from the original man page from John Gilmore.
This was withdrawn in version 1.11. Thomas Bushnell, n/BSG and Amy
Gorin worked on a tutorial and manual for GNU tar.
François Pinard put version 1.11.8 of the manual together by
taking information from all these sources and merging them. Melissa
Weisshaus finally edited and redesigned the book to create version
1.12. The book for versions from 1.14 up to 1.22 were edited
by the current maintainer, Sergey Poznyakoff.
For version 1.12, Daniel Hagerty contributed a great deal of technical consulting. In particular, he is the primary author of Performing Backups and Restoring Files.
In July, 2003 GNU tar was put on CVS at savannah.gnu.org
(see http://savannah.gnu.org/projects/tar), and
active development and maintenance work has started
again. Currently GNU tar is being maintained by Paul Eggert, Sergey
Poznyakoff and Jeff Bailey.
Support for POSIX archives was added by Sergey Poznyakoff.
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If you find problems or have suggestions about this program or manual, please report them to ‘bug-tar@gnu.org’.
When reporting a bug, please be sure to include as much detail as possible, in order to reproduce it. .
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tar This chapter guides you through some basic examples of three tar
operations: ‘--create’, ‘--list’, and ‘--extract’. If
you already know how to use some other version of tar, then you
may not need to read this chapter. This chapter omits most complicated
details about how tar works.
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This chapter is paced to allow beginners to learn about tar
slowly. At the same time, we will try to cover all the basic aspects of
these three operations. In order to accomplish both of these tasks, we
have made certain assumptions about your knowledge before reading this
manual, and the hardware you will be using:
tar commands in. When we show file names,
we will assume that those names are relative to your home directory.
For example, my home directory is ‘/home/fsf/melissa’. All of
my examples are in a subdirectory of the directory named by that file
name; the subdirectory is called ‘practice’.
tar archives with tape drives.
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In the examples, ‘$’ represents a typical shell prompt. It
precedes lines you should type; to make this more clear, those lines are
shown in this font, as opposed to lines which represent the
computer's response; those lines are shown in this font, or
sometimes ‘like this’.
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tar Operations and Options tar can take a wide variety of arguments which specify and define
the actions it will have on the particular set of files or the archive.
The main types of arguments to tar fall into one of two classes:
operations, and options.
Some arguments fall into a class called operations; exactly one of
these is both allowed and required for any instance of using tar;
you may not specify more than one. People sometimes speak of
operating modes. You are in a particular operating mode when you
have specified the operation which specifies it; there are eight
operations in total, and thus there are eight operating modes.
The other arguments fall into the class known as options. You are
not required to specify any options, and you are allowed to specify more
than one at a time (depending on the way you are using tar at
that time). Some options are used so frequently, and are so useful for
helping you type commands more carefully that they are effectively
“required”. We will discuss them in this chapter.
You can write most of the tar operations and options in any
of three forms: long (mnemonic) form, short form, and old style. Some
of the operations and options have no short or “old” forms; however,
the operations and options which we will cover in this tutorial have
corresponding abbreviations. We will indicate those abbreviations
appropriately to get you used to seeing them. (Note that the “old
style” option forms exist in GNU tar for compatibility with Unix
tar. In this book we present a full discussion of this way
of writing options and operations (see section Old Option Style), and we discuss
the other two styles of writing options (See section Long Option Style, and
see section Short Option Style).
In the examples and in the text of this tutorial, we usually use the
long forms of operations and options; but the “short” forms produce
the same result and can make typing long tar commands easier.
For example, instead of typing
tar --create --verbose --file=afiles.tar apple angst aspic |
you can type
tar -c -v -f afiles.tar apple angst aspic |
or even
tar -cvf afiles.tar apple angst aspic |
For more information on option syntax, see Advanced GNU tar Operations. In
discussions in the text, when we name an option by its long form, we
also give the corresponding short option in parentheses.
The term, “option”, can be confusing at times, since “operations”
are often lumped in with the actual, optional “options” in certain
general class statements. For example, we just talked about “short and
long forms of options and operations”. However, experienced tar
users often refer to these by shorthand terms such as, “short and long
options”. This term assumes that the “operations” are included, also.
Context will help you determine which definition of “options” to use.
Similarly, the term “command” can be confusing, as it is often used in
two different ways. People sometimes refer to tar “commands”.
A tar command is the entire command line of user input
which tells tar what to do — including the operation, options,
and any arguments (file names, pipes, other commands, etc.). However,
you will also sometimes hear the term “the tar command”. When
the word “command” is used specifically like this, a person is usually
referring to the tar operation, not the whole line.
Again, use context to figure out which of the meanings the speaker
intends.
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Here are the three most frequently used operations (both short and long forms), as well as a brief description of their meanings. The rest of this chapter will cover how to use these operations in detail. We will present the rest of the operations in the next chapter.
Create a new tar archive.
List the contents of an archive.
Extract one or more members from an archive.
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To understand how to run tar in the three operating modes listed
previously, you also need to understand how to use two of the options to
tar: ‘--file’ (which takes an archive file as an argument)
and ‘--verbose’. (You are usually not required to specify
either of these options when you run tar, but they can be very
useful in making things more clear and helping you avoid errors.)
| The ‘--file’ Option | ||
| The ‘--verbose’ Option | ||
| Getting Help: Using the ‘--help’ Option |
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Specify the name of an archive file.
You can specify an argument for the ‘--file=archive-name’ (‘-f archive-name’) option whenever you
use tar; this option determines the name of the archive file
that tar will work on.
If you don't specify this argument, then tar will examine
the environment variable TAPE. If it is set, its value will be
used as the archive name. Otherwise, tar will use the
default archive, determined at the compile time. Usually it is
standard output or some physical tape drive attached to your machine
(you can verify what the default is by running tar
--show-defaults, see section Obtaining GNU tar default values). If there is no tape drive
attached, or the default is not meaningful, then tar will
print an error message. The error message might look roughly like one
of the following:
tar: can't open /dev/rmt8 : No such device or address tar: can't open /dev/rsmt0 : I/O error |
To avoid confusion, we recommend that you always specify an archive file
name by using ‘--file=archive-name’ (‘-f archive-name’) when writing your tar commands.
For more information on using the ‘--file=archive-name’ (‘-f archive-name’) option, see
Choosing and Naming Archive Files.
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Show the files being worked on as tar is running.
‘--verbose’ (‘-v’) shows details about the results of running
tar. This can be especially useful when the results might not be
obvious. For example, if you want to see the progress of tar as
it writes files into the archive, you can use the ‘--verbose’
option. In the beginning, you may find it useful to use
‘--verbose’ at all times; when you are more accustomed to
tar, you will likely want to use it at certain times but not at
others. We will use ‘--verbose’ at times to help make something
clear, and we will give many examples both using and not using
‘--verbose’ to show the differences.
Each instance of ‘--verbose’ on the command line increases the verbosity level by one, so if you need more details on the output, specify it twice.
When reading archives (‘--list’, ‘--extract’,
‘--diff’), tar by default prints only the names of
the members being extracted. Using ‘--verbose’ will show a full,
ls style member listing.
In contrast, when writing archives (‘--create’, ‘--append’,
‘--update’), tar does not print file names by
default. So, a single ‘--verbose’ option shows the file names
being added to the archive, while two ‘--verbose’ options
enable the full listing.
For example, to create an archive in verbose mode:
$ tar -cvf afiles.tar apple angst aspic apple angst aspic |
Creating the same archive with the verbosity level 2 could give:
$ tar -cvvf afiles.tar apple angst aspic -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic |
This works equally well using short or long forms of options. Using long forms, you would simply write out the mnemonic form of the option twice, like this:
$ tar --create --verbose --verbose … |
Note that you must double the hyphens properly each time.
Later in the tutorial, we will give examples using ‘--verbose --verbose’.
The full output consists of six fields:
ls -l output (see format=verbose: (fileutils)What information is listed section `Verbose listing' in GNU file utilities).
Depending on the file type, the name can be followed by some additional information, described in the following table:
The file or archive member is a symbolic link and link-name is the name of file it links to.
The file or archive member is a hard link and link-name is the name of file it links to.
The archive member is an old GNU format long link. You will normally not encounter this.
The archive member is an old GNU format long name. You will normally not encounter this.
The archive member is a GNU volume header (see section Tape Files).
Encountered only at the beginning of a multi-volume archive (see section Using Multiple Tapes). This archive member is a continuation from the previous volume. The number n gives the offset where the original file was split.
An archive member of unknown type. c is the type character from
the archive header. If you encounter such a message, it means that
either your archive contains proprietary member types GNU tar is not
able to handle, or the archive is corrupted.
For example, here is an archive listing containing most of the special suffixes explained above:
V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header-- -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at byte 32456-- -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues |
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The ‘--help’ option to tar prints out a very brief list of
all operations and option available for the current version of
tar available on your system.
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(This message will disappear, once this node revised.)
One of the basic operations of tar is ‘--create’ (‘-c’), which
you use to create a tar archive. We will explain
‘--create’ first because, in order to learn about the other
operations, you will find it useful to have an archive available to
practice on.
To make this easier, in this section you will first create a directory containing three files. Then, we will show you how to create an archive (inside the new directory). Both the directory, and the archive are specifically for you to practice on. The rest of this chapter and the next chapter will show many examples using this directory and the files you will create: some of those files may be other directories and other archives.
The three files you will archive in this example are called ‘blues’, ‘folk’, and ‘jazz’. The archive is called ‘collection.tar’.
This section will proceed slowly, detailing how to use ‘--create’
in verbose mode, and showing examples using both short and long
forms. In the rest of the tutorial, and in the examples in the next
chapter, we will proceed at a slightly quicker pace. This section
moves more slowly to allow beginning users to understand how
tar works.
| 2.6.1 Preparing a Practice Directory for Examples | ||
| 2.6.2 Creating the Archive | ||
| 2.6.3 Running ‘--create’ with ‘--verbose’ | ||
| 2.6.4 Short Forms with ‘create’ | ||
| 2.6.5 Archiving Directories |
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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 section 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.
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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. You could also say:
$ tar blues --create folk --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 section 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 section 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 section 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 section How to Add Files to Existing Archives: ‘--append’.
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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 the remaining 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.
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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 blues --create folk --file=collection.tar jazz |
is confusing as it is. When shown using short forms, however, it becomes much more so:
$ tar blues -c folk -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.
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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 section 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.
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Frequently, you will find yourself wanting to determine exactly what a particular archive contains. You can use the ‘--list’ (‘-t’) operation to get the member names as they currently appear in the archive, as well as various attributes of the files at the time they were archived. For example, you can examine the archive ‘collection.tar’ that you created in the last section with the command,
$ tar --list --file=collection.tar |
The output of tar would then be:
blues folk jazz |
The archive ‘bfiles.tar’ would list as follows:
./birds baboon ./box |
Be sure to use a ‘--file=archive-name’ (‘-f archive-name’) option just as with ‘--create’ (‘-c’) to specify the name of the archive.
If you use the ‘--verbose’ (‘-v’) option with
‘--list’, then tar will print out a listing
reminiscent of ‘ls -l’, showing owner, file size, and so
forth. This output is described in detail in verbose member listing.
If you had used ‘--verbose’ (‘-v’) mode, the example above would look like:
$ tar --list --verbose --file=collection.tar folk -rw-r--r-- myself user 62 1990-05-23 10:55 folk |
It is important to notice that the output of tar --list
--verbose does not necessarily match that produced by tar
--create --verbose while creating the archive. It is because
GNU tar, unless told explicitly not to do so, removes some directory
prefixes from file names before storing them in the archive
(See section Absolute File Names, for more information). In other
words, in verbose mode GNU tar shows file names when creating
an archive and member names when listing it. Consider this
example:
$ tar --create --verbose --file archive /etc/mail tar: Removing leading `/' from member names /etc/mail/ /etc/mail/sendmail.cf /etc/mail/aliases $ tar --test --file archive etc/mail/ etc/mail/sendmail.cf etc/mail/aliases |
This default behavior can sometimes be inconvenient. You can force
GNU tar show member names when creating archive by supplying
‘--show-stored-names’ option.
Print member (as opposed to file) names when creating the archive.
You can specify one or more individual member names as arguments when
using ‘list’. In this case, tar will only list the
names of members you identify. For example, tar --list
--file=afiles.tar apple would only print ‘apple’.
Because tar preserves file names, these must be specified as
they appear in the archive (i.e., relative to the directory from which
the archive was created). Therefore, it is essential when specifying
member names to tar that you give the exact member names.
For example, tar --list --file=bfiles.tar birds would produce an
error message something like ‘tar: birds: Not found in archive’,
because there is no member named ‘birds’, only one named
‘./birds’. While the names ‘birds’ and ‘./birds’ name
the same file, member names by default are compared verbatim.
However, tar --list --file=bfiles.tar baboon would respond with ‘baboon’, because this exact member name is in the archive file ‘bfiles.tar’. If you are not sure of the exact file name, use globbing patterns, for example:
$ tar --list --file=bfiles.tar --wildcards '*b*' |
will list all members whose name contains ‘b’. See section Wildcards Patterns and Matching,
for a detailed discussion of globbing patterns and related
tar command line options.
| Listing the Contents of a Stored Directory |
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To get information about the contents of an archived directory, use the directory name as a file name argument in conjunction with ‘--list’ (‘-t’). To find out file attributes, include the ‘--verbose’ (‘-v’) option.
For example, to find out about files in the directory ‘practice’, in the archive file ‘music.tar’, type:
$ tar --list --verbose --file=music.tar practice |
tar responds:
drwxrwxrwx myself user 0 1990-05-31 21:49 practice/ -rw-r--r-- myself user 42 1990-05-21 13:29 practice/blues -rw-r--r-- myself user 62 1990-05-23 10:55 practice/folk -rw-r--r-- myself user 40 1990-05-21 13:30 practice/jazz -rw-r--r-- myself user 10240 1990-05-31 21:49 practice/collection.tar |
When you use a directory name as a file name argument, tar acts on
all the files (including sub-directories) in that directory.
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Creating an archive is only half the job—there is no point in storing files in an archive if you can't retrieve them. The act of retrieving members from an archive so they can be used and manipulated as unarchived files again is called extraction. To extract files from an archive, use the ‘--extract’ (‘--get’ or ‘-x’) operation. As with ‘--create’, specify the name of the archive with ‘--file’ (‘-f’) option. Extracting an archive does not modify the archive in any way; you can extract it multiple times if you want or need to.
Using ‘--extract’, you can extract an entire archive, or specific files. The files can be directories containing other files, or not. As with ‘--create’ (‘-c’) and ‘--list’ (‘-t’), you may use the short or the long form of the operation without affecting the performance.
| 2.8.1 Extracting an Entire Archive | ||
| 2.8.2 Extracting Specific Files | ||
| 2.8.3 Extracting Files that are Directories | ||
| 2.8.4 Extracting Archives from Untrusted Sources | ||
| 2.8.5 Commands That Will Fail |
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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-- 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 |
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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. tar --extract --file=bfiles.tar birds will fail, because there is no member named ‘birds’. To extract the member named ‘./birds’, you must specify tar --extract --file=bfiles.tar ./birds. If you don't remember the exact member names, use ‘--list’ (‘-t’) option (see section How to List Archives). You can also extract those members that match a specific globbing pattern. For example, to extract from ‘bfiles.tar’ all files that begin with ‘b’, no matter their directory prefix, you could type:
$ tar -x -f bfiles.tar --wildcards --no-anchored 'b*' |
Here, ‘--wildcards’ instructs tar to treat
command line arguments as globbing patterns and ‘--no-anchored’
informs it that the patterns apply to member names after any ‘/’
delimiter. The use of globbing patterns is discussed in detail in
See section Wildcards Patterns and Matching.
You can extract a file to standard output by combining the above options with the ‘--to-stdout’ (‘-O’) option (see section Writing to Standard Output).
If you give the ‘--verbose’ option, then ‘--extract’ will print the names of the archive members as it extracts them.
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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 section 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.
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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’).
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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/folk practice/jazz practice/rock |
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.
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tar (This message will disappear, once this node revised.)
This chapter is about how one invokes the GNU tar
command, from the command synopsis (see section General Synopsis of tar). There are
numerous options, and many styles for writing them. One mandatory
option specifies the operation tar should perform
(see section Operations), other options are meant to detail how
this operation should be performed (see section tar Options).
Non-option arguments are not always interpreted the same way,
depending on what the operation is.
You will find in this chapter everything about option styles and rules for
writing them (see section The Three Option Styles). On the other hand, operations and options
are fully described elsewhere, in other chapters. Here, you will find
only synthetic descriptions for operations and options, together with
pointers to other parts of the tar manual.
Some options are so special they are fully described right in this
chapter. They have the effect of inhibiting the normal operation of
tar or else, they globally alter the amount of feedback the user
receives about what is going on. These are the ‘--help’ and
‘--version’ (see section GNU tar documentation), ‘--verbose’ (see section Checking tar progress)
and ‘--interactive’ options (see section Asking for Confirmation During Operations).
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tar The GNU tar program is invoked as either one of:
tar option… [name]… tar letter… [argument]… [option]… [name]… |
The second form is for when old options are being used.
You can use tar to store files in an archive, to extract them from
an archive, and to do other types of archive manipulation. The primary
argument to tar, which is called the operation, specifies
which action to take. The other arguments to tar are either
options, which change the way tar performs an operation,
or file names or archive members, which specify the files or members
tar is to act on.
You can actually type in arguments in any order, even if in this manual
the options always precede the other arguments, to make examples easier
to understand. Further, the option stating the main operation mode
(the tar main command) is usually given first.
Each name in the synopsis above is interpreted as an archive member
name when the main command is one of ‘--compare’
(‘--diff’, ‘-d’), ‘--delete’, ‘--extract’
(‘--get’, ‘-x’), ‘--list’ (‘-t’) or
‘--update’ (‘-u’). When naming archive members, you
must give the exact name of the member in the archive, as it is
printed by ‘--list’. For ‘--append’ (‘-r’) and
‘--create’ (‘-c’), these name arguments specify
the names of either files or directory hierarchies to place in the archive.
These files or hierarchies should already exist in the file system,
prior to the execution of the tar command.
tar interprets relative file names as being relative to the
working directory. tar will make all file names relative
(by removing leading slashes when archiving or restoring files),
unless you specify otherwise (using the ‘--absolute-names’
option). See section Absolute File Names, for more information about
‘--absolute-names’.
If you give the name of a directory as either a file name or a member
name, then tar acts recursively on all the files and directories
beneath that directory. For example, the name ‘/’ identifies all
the files in the file system to tar.
The distinction between file names and archive member names is especially
important when shell globbing is used, and sometimes a source of confusion
for newcomers. See section Wildcards Patterns and Matching, for more information about globbing.
The problem is that shells may only glob using existing files in the
file system. Only tar itself may glob on archive members, so when
needed, you must ensure that wildcard characters reach tar without
being interpreted by the shell first. Using a backslash before ‘*’
or ‘?’, or putting the whole argument between quotes, is usually
sufficient for this.
Even if names are often specified on the command line, they can also be read from a text file in the file system, using the ‘--files-from=file-of-names’ (‘-T file-of-names’) option.
If you don't use any file name arguments, ‘--append’ (‘-r’),
‘--delete’ and ‘--concatenate’ (‘--catenate’,
‘-A’) will do nothing, while ‘--create’ (‘-c’)
will usually yield a diagnostic and inhibit tar execution.
The other operations of tar (‘--list’,
‘--extract’, ‘--compare’, and ‘--update’)
will act on the entire contents of the archive.
Besides successful exits, GNU tar may fail for
many reasons. Some reasons correspond to bad usage, that is, when the
tar command line is improperly written. Errors may be
encountered later, while processing the archive or the files. Some
errors are recoverable, in which case the failure is delayed until
tar has completed all its work. Some errors are such that
it would be not meaningful, or at least risky, to continue processing:
tar then aborts processing immediately. All abnormal exits,
whether immediate or delayed, should always be clearly diagnosed on
stderr, after a line stating the nature of the error.
Possible exit codes of GNU tar are summarized in the following
table:
‘Successful termination’.
‘Some files differ’. If tar was invoked with ‘--compare’ (‘--diff’, ‘-d’) command line option, this means that some files in the archive differ from their disk counterparts (see section Comparing Archive Members with the File System). If tar was given ‘--create’, ‘--append’ or ‘--update’ option, this exit code means that some files were changed while being archived and so the resulting archive does not contain the exact copy of the file set.
‘Fatal error’. This means that some fatal, unrecoverable error occurred.
If tar has invoked a subprocess and that subprocess exited with a
nonzero exit code, tar exits with that code as well.
This can happen, for example, if tar was given some
compression option (see section Creating and Reading Compressed Archives) and the external compressor program
failed. Another example is rmt failure during backup to the
remote device (see section The Remote Tape Server).
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tar Options GNU tar has a total of eight operating modes which
allow you to perform a variety of tasks. You are required to choose
one operating mode each time you employ the tar program by
specifying one, and only one operation as an argument to the
tar command (the corresponding options may be found
at The Three Most Frequently Used Operations and The Five Advanced tar Operations). Depending on
circumstances, you may also wish to customize how the chosen operating
mode behaves. For example, you may wish to change the way the output
looks, or the format of the files that you wish to archive may require
you to do something special in order to make the archive look right.
You can customize and control tar's performance by running
tar with one or more options (such as ‘--verbose’
(‘-v’), which we used in the tutorial). As we said in the
tutorial, options are arguments to tar which are (as
their name suggests) optional. Depending on the operating mode, you
may specify one or more options. Different options will have different
effects, but in general they all change details of the operation, such
as archive format, archive name, or level of user interaction. Some
options make sense with all operating modes, while others are
meaningful only with particular modes. You will likely use some
options frequently, while you will only use others infrequently, or
not at all. (A full list of options is available in see section All tar Options.)
The TAR_OPTIONS environment variable specifies default options to
be placed in front of any explicit options. For example, if
TAR_OPTIONS is ‘-v --unlink-first’, tar behaves as
if the two options ‘-v’ and ‘--unlink-first’ had been
specified before any explicit options. Option specifications are
separated by whitespace. A backslash escapes the next character, so it
can be used to specify an option containing whitespace or a backslash.
Note that tar options are case sensitive. For example, the
options ‘-T’ and ‘-t’ are different; the first requires an
argument for stating the name of a file providing a list of names,
while the second does not require an argument and is another way to
write ‘--list’ (‘-t’).
In addition to the eight operations, there are many options to
tar, and three different styles for writing both: long (mnemonic)
form, short form, and old style. These styles are discussed below.
Both the options and the operations can be written in any of these three
styles.
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There are three styles for writing operations and options to the command
line invoking tar. The different styles were developed at
different times during the history of tar. These styles will be
presented below, from the most recent to the oldest.
Some options must take an argument. (For example, ‘--file’
(‘-f’)) takes the name of an archive file as an argument. If
you do not supply an archive file name, tar will use a
default, but this can be confusing; thus, we recommend that you always
supply a specific archive file name.) Where you place the
arguments generally depends on which style of options you choose. We
will detail specific information relevant to each option style in the
sections on the different option styles, below. The differences are
subtle, yet can often be very important; incorrect option placement
can cause you to overwrite a number of important files. We urge you
to note these differences, and only use the option style(s) which
makes the most sense to you until you feel comfortable with the others.
Some options may take an argument. Such options may have at most long and short forms, they do not have old style equivalent. The rules for specifying an argument for such options are stricter than those for specifying mandatory arguments. Please, pay special attention to them.
| 3.3.1 Long Option Style | ||
| 3.3.2 Short Option Style | ||
| 3.3.3 Old Option Style | ||
| 3.3.4 Mixing Option Styles |
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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’.
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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 argument(2).
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.
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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(3). 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’.
On the other hand, this old style syntax makes 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.
Old options are kept for compatibility with old versions of tar.
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 |
As far as we know, all tar programs, GNU and
non-GNU, support old options. GNU tar
supports them not only for historical reasons, but also because many
people are used to them. For compatibility with Unix tar,
the first argument is always treated as containing command and option
letters even if it doesn't start with ‘-’. Thus, ‘tar c’ is
equivalent to ‘tar -c’: both of them specify the
‘--create’ (‘-c’) command to create an archive.
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All three styles may be intermixed in a single tar command,
so long as the rules for each style are fully
respected(4). 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.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
tar Options The coming manual sections contain an alphabetical listing of all
tar operations and options, with brief descriptions and cross
references to more in-depth explanations in the body of the manual.
They also contain an alphabetically arranged table of the short option
forms with their corresponding long option. You can use this table as
a reference for deciphering tar commands in scripts.
| 3.4.1 Operations | ||
3.4.2 tar Options | ||
| 3.4.3 Short Options Cross Reference |
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
Appends files to the end of the archive. See section How to Add Files to Existing Archives: ‘--append’.
Same as ‘--concatenate’. See section Combining Archives with ‘--concatenate’.
Compares archive members with their counterparts in the file system, and reports differences in file size, mode, owner, modification date and contents. See section Comparing Archive Members with the File System.
Appends other tar archives to the end of the archive.
See section Combining Archives with ‘--concatenate’.
Creates a new tar archive. See section How to Create Archives.
Deletes members from the archive. Don't try this on a archive on a tape! See section Removing Archive Members Using ‘--delete’.
Same ‘--compare’. See section Comparing Archive Members with the File System.
Extracts members from the archive into the file system. See section How to Extract Members from an Archive.
Same as ‘--extract’. See section How to Extract Members from an Archive.
Lists the members in an archive. See section How to List Archives.
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 section Updating an Archive.
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tar Options Normally when creating an archive, tar strips an initial
‘/’ from member names. This option disables that behavior.
See section Absolute File Names.
(See ‘--newer’, see section Operating Only on New Files)
A pattern must match an initial subsequence of the name's components. See section Controlling Pattern-Matching.
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 system does not support
‘--atime-preserve=system’, you might be able to preserve access
times reliably by 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.
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 section Creating and Reading Compressed Archives.
Rather than deleting files from the file system, tar will
back them up using simple or numbered backups, depending upon
backup-type. See section Backup options.
With this option present, tar prints error messages for read errors
with the block number in the archive file. See block-number.
Sets the blocking factor tar uses to blocking x 512 bytes per
record. See section The Blocking Factor of an Archive.
This option tells tar to read or write archives through
bzip2. See section Creating and Reading Compressed Archives.
Check device numbers when creating a list of modified files for incremental archiving. This is the default. See device numbers, for a detailed description.
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
‘--checklist-action’ below. For a detailed description, see
Checkpoints.
Instruct tar to execute an action upon hitting a
breakpoint. Here we give only a brief outline. See section Checkpoints,
for a complete description.
The action argument can be one of the following:
Produce an audible bell on the console.
Print a single dot on the standard listing stream.
Display a textual message on the standard error, with the status and number of the checkpoint. This is the default.
Display string on the standard error. Before output, the string is subject to meta-character expansion.
Execute the given command.
Wait for time seconds.
Output string on the current console (‘/dev/tty’).
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.
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 section Hard Links.
tar will use the compress program when reading or
writing the archive. This allows you to directly act on archives
while saving space. See section Creating and Reading Compressed Archives.
(See ‘--interactive’.) See section Asking for Confirmation During Operations.
Delay setting modification times and permissions of extracted directories until the end of extraction. See section Directory Modification Times and Permissions.
When creating a tar archive, tar will archive the
file that a symbolic link points to, rather than archiving the
symlink. See section Symbolic Links.
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 section Changing the Working Directory.
When performing operations, tar will skip files that match
pattern. See section Excluding Some Files.
Similar to ‘--exclude’, except tar will use the list of
patterns in the file file. See section Excluding Some Files.
Exclude from dump any directory containing a valid cache directory tag file, but still dump the directory node and the tag file itself.
See section Excluding Some Files.
Exclude from dump any directory containing a valid cache directory tag file, but still dump the directory node itself.
See section Excluding Some Files.
Exclude from dump any directory containing a valid cache directory tag file. See section Excluding Some Files.
Exclude from dump any directory containing file named file, but dump the directory node and file itself. See section Excluding Some Files.
Exclude from dump the contents of any directory containing file named file, but dump the directory node itself. See section Excluding Some Files.
Exclude from dump any directory containing file named file. See section Excluding Some Files.
Exclude from dump directories and files, that are internal for some widely used version control systems.
See section Excluding Some Files.
tar will use the file archive as the tar archive it
performs operations on, rather than tar's compilation dependent
default. See section The ‘--file’ Option.
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 section Reading Names from a File.
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.
Selects output archive format. Format may be one of the following:
Creates an archive that is compatible with Unix V7 tar.
Creates an archive that is compatible with GNU tar version
1.12 or earlier.
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.
Creates a POSIX.1-1988 compatible archive.
Creates a POSIX.1-2001 archive.
See section Controlling the Archive Format, for a detailed discussion of these formats.
Files added to the tar archive will have a group ID of group,
rather than the group from the source file. group is first decoded
as a group symbolic name, but if this interpretation fails, it has to be
a decimal numeric group ID. See section Overriding File Metadata.
Also see the comments for the ‘--owner=user’ option.
This option tells tar to read or write archives through
gzip, allowing tar to directly operate on several
kinds of compressed archives transparently. See section Creating and Reading Compressed Archives.
When creating an archive, dereference hard links and store the files they refer to, instead of creating usual hard link members.
See section Hard Links.
tar will print out a short message summarizing the operations and
options to tar and exit. See section GNU tar documentation.
Ignore case when matching member or file names with patterns. See section Controlling Pattern-Matching.
Ignore exit codes of subprocesses. See section Writing to an External Program.
Do not exit unsuccessfully merely because an unreadable file was encountered. See section Options to Help Read Archives.
With this option, tar will ignore zeroed blocks in the
archive, which normally signals EOF. See section Options to Help Read Archives.
Informs tar that it is working with an old
GNU-format incremental backup archive. It is intended
primarily for backwards compatibility only. See section Using tar to Perform Incremental Dumps,
for a detailed discussion of incremental archives.
Send verbose output to file instead of to standard output.
When tar is performing multi-tape backups, script-file is run
at the end of each tape. If script-file exits with nonzero status,
tar fails immediately. See info-script, for a detailed
discussion of script-file.
Specifies that tar should ask the user for confirmation before
performing potentially destructive options, such as overwriting files.
See section Asking for Confirmation During Operations.
Do not replace existing files that are newer than their archive copies when extracting files from an archive.
Do not overwrite existing files when extracting files from an archive. See section Keep Old Files.
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 section Tape Files.
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 section Using tar to Perform Incremental Dumps.
This option tells tar to read or write archives through
lzma. See section Creating and Reading Compressed Archives.
This option tells tar to read or write archives through
lzop. See section Creating and Reading Compressed Archives.
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 section Overriding File Metadata.
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 section 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 section Overriding File Metadata.
Informs tar that it should create or otherwise operate on a
multi-volume tar archive. See section Using Multiple Tapes.
(see –info-script)
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 section Operating Only on New Files.
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 section Operating Only on New Files.
An exclude pattern can match any subsequence of the name's components. See section Controlling Pattern-Matching.
Disables automatic compressed format recognition based on the archive suffix. See –auto-compress. See section Creating and Reading Compressed Archives.
Do not check device numbers when creating a list of modified files for incremental archiving. See device numbers, for a detailed description.
Modification times and permissions of extracted directories are set when all files from this directory have been extracted. This is the default. See section Directory Modification Times and Permissions.
Use case-sensitive matching. See section Controlling Pattern-Matching.
Print warnings about subprocesses that terminated with a nonzero exit code. See section Writing to an External Program.
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.
Preserve metadata of existing directories when extracting files from an archive. See section Overwrite Old Files.
Remove characters listed in string from the list of quoted characters set by the previous ‘--quote-chars’ option (see section Quoting Member Names).
With this option, tar will not recurse into directories.
See section Descending into Directories.
When extracting an archive, do not attempt to preserve the owner
specified in the tar archive. This the default behavior
for ordinary users.
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.
Treat all input file or member names literally, do not interpret escape sequences. See input name quoting.
Do not use wildcards. See section Controlling Pattern-Matching.
Wildcards do not match ‘/’. See section Controlling Pattern-Matching.
When tar is using the ‘--files-from’ option, this option
instructs tar to expect file names terminated with NUL, so
tar can correctly work with file names that contain newlines.
See section NUL Terminated File Names.
This option will notify tar that it should use numeric user
and group IDs when creating a tar file, rather than names.
See section Handling File Attributes.
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 section Changes, for more information.
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.
Synonym for ‘--format=v7’.
Used when creating an archive. Prevents tar from recursing into
directories that are on different file systems from the current
directory.
Overwrite existing files and directory metadata when extracting files from an archive. See section Overwrite Old Files.
Overwrite the metadata of existing directories when extracting files from an archive. See section Overwrite Old Files.
Specifies that tar should use user as the owner of members
when creating archives, instead of the user associated with the source
file. user is first decoded as a user symbolic name, but if
this interpretation fails, it has to be a decimal numeric user ID.
See section Overriding File Metadata.
This option does not affect extraction from archives.
This option is meaningful only with POSIX.1-2001 archives
(see section GNU tar and POSIX tar). It modifies the way tar handles the
extended header keywords. Keyword-list is a comma-separated
list of keyword options. See section Controlling Extended Header Keywords, for a detailed
discussion.
Synonym for ‘--format=v7’.
Same as ‘--format=posix’.
Synonymous with specifying both ‘--preserve-permissions’ and ‘--same-order’. See section Setting Access Permissions.
(See ‘--same-order’; see section Options to Help Read Archives.)
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 section Setting Access Permissions.
Always quote characters from string, even if the selected quoting style would not quote them (see section Quoting Member Names).
Set quoting style to use when printing member and file names
(see section 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.
Specifies that tar should reblock its input, for reading
from pipes on systems with buggy implementations. See section Options to Help Read Archives.
Instructs tar to use size bytes per record when accessing the
archive. See section The Blocking Factor of an Archive.
With this option, tar recurses into directories (default).
See section Descending into Directories.
Remove existing directory hierarchies before extracting directories of the same name from the archive. See section Recursive Unlink.
Directs tar to remove the source file from the file system after
appending it to an archive. See section Removing Files.
Disable use of some potentially harmful tar options.
Currently this option disables shell invocation from multi-volume menu
(see section Using Multiple Tapes).
Notifies tar that it should use cmd instead of
the default ‘/usr/libexec/rmt’ (see section The Remote Tape Server).
Notifies tar that is should use cmd to communicate with remote
devices. See section Device Selection and Switching.
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 section Options to Help Read Archives.
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 section Handling File Attributes.
(See ‘--preserve-permissions’; see section Setting Access Permissions.)
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.
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 |
Instructs tar to mention the directories it is skipping when
operating on a tar archive. See show-omitted-dirs.
Display file or member names after applying any transformations
(see section 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.
Invokes a GNU extension when adding files to an archive that handles sparse files efficiently. See section Archiving Sparse Files.
Specifies the format version to use when archiving sparse files. Implies ‘--sparse’. See section Archiving Sparse Files. For the description of the supported sparse formats, See section Storing Sparse Files.
This option affects extraction only; tar will skip extracting
files in the archive until it finds one that matches name.
See section Coping with Scarce Resources.
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’.
Alters the suffix tar uses when backing up files from the default
‘~’. See section Backup options.
Specifies the length of tapes that tar is writing as being
num x 1024 bytes long. See section Using Multiple Tapes.
Reads the volume label. If an argument is specified, test whether it matches the volume label. See –test-label option.
During extraction tar will pipe extracted files to the
standard input of command. See section Writing to an External Program.
During extraction, tar will extract files to stdout rather
than to the file system. See section Writing to Standard Output.
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.
Sets the data modification time of extracted files to the extraction time, rather than the data modification time stored in the archive. See section Setting Data Modification Times.
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 section Modifying File and Member Names.
To see transformed member names in verbose listings, use ‘--show-transformed-names’ option (see show-transformed-names).
(See ‘--compress’. see section Creating and Reading Compressed Archives)
(See ‘--gzip’. see section Creating and Reading Compressed Archives)
Directs tar to remove the corresponding file from the file
system before extracting it from the archive. See section Unlink First.
Enable unquoting input file or member names (default). See input name quoting.
Instructs tar to access the archive through prog, which is
presumed to be a compression program of some sort. See section Creating and Reading Compressed Archives.
Display file modification dates in UTC. This option implies ‘--verbose’.
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 section Checking tar progress.
Verifies that the archive was correctly written when creating an archive. See section Verifying Data as It is Stored.
Print information about the program's name, version, origin and legal
status, all on standard output, and then exit successfully.
See section GNU tar documentation.
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.
Use wildcards when matching member names with patterns. See section Controlling Pattern-Matching.
Wildcards match ‘/’. See section Controlling Pattern-Matching.
Use xz for compressing or decompressing the archives. See section Creating and Reading Compressed Archives.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
Here is an alphabetized list of all of the short option forms, matching them with the equivalent long option.
Short Option | Reference |
|---|---|
-A | |
-B | |
-C | |
-F | |
-G | |
-J | –xz. |
-K | |
-L | |
-M | |
-N | |
-O | |
-P | |
-R | |
-S | |
-T | |
-U | |
-V | |
-W | |
-X | |
-Z | |
-b | |
-c | |
-d | |
-f | |
-g | |
-h | |
-i | |
-j | |
-k | |
-l | |
-m | |
-o | When creating, –no-same-owner, when extracting — –portability. The latter usage is deprecated. It is retained for compatibility with
the earlier versions of GNU |
-p | |
-r | |
-s | |
-t | |
-u | |
-v | |
-w | |
-x | |
-z |
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
tar documentation Being careful, the first thing is really checking that you are using
GNU tar, indeed. The ‘--version’ option
causes tar to print information about its name, version,
origin and legal status, all on standard output, and then exit
successfully. For example, ‘tar --version’ might print:
tar (GNU tar) 1.22 Copyright (C) 2008 Free Software Foundation, Inc. This is free software. You may redistribute copies of it under the terms of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>. There is NO WARRANTY, to the extent permitted by law. Written by John Gilmore and Jay Fenlason. |
The first occurrence of ‘tar’ in the result above is the program
name in the package (for example, rmt is another program),
while the second occurrence of ‘tar’ is the name of the package
itself, containing possibly many programs. The package is currently
named ‘tar’, after the name of the main program it
contains(6).
Another thing you might want to do is checking the spelling or meaning
of some particular tar option, without resorting to this
manual, for once you have carefully read it. GNU tar
has a short help feature, triggerable through the
‘--help’ option. By using this option, tar will
print a usage message listing all available options on standard
output, then exit successfully, without doing anything else and
ignoring all other options. Even if this is only a brief summary, it
may be several screens long. So, if you are not using some kind of
scrollable window, you might prefer to use something like:
$ tar --help | less |
presuming, here, that you like using less for a pager. Other
popular pagers are more and pg. If you know about some
keyword which interests you and do not want to read all the
‘--help’ output, another common idiom is doing:
tar --help | grep keyword |
for getting only the pertinent lines. Notice, however, that some
tar options have long description lines and the above
command will list only the first of them.
The exact look of the option summary displayed by tar --help is configurable. See section Configuring Help Summary, for a detailed description.
If you only wish to check the spelling of an option, running tar
--usage may be a better choice. This will display a terse list of
tar option without accompanying explanations.
The short help output is quite succinct, and you might have to get
back to the full documentation for precise points. If you are reading
this paragraph, you already have the tar manual in some
form. This manual is available in a variety of forms from
http://www.gnu.org/software/tar/manual. It may be printed out of the GNU tar
distribution, provided you have TeX already installed somewhere,
and a laser printer around. Just configure the distribution, execute
the command ‘make dvi’, then print ‘doc/tar.dvi’ the
usual way (contact your local guru to know how). If GNU tar
has been conveniently installed at your place, this
manual is also available in interactive, hypertextual form as an Info
file. Just call ‘info tar’ or, if you do not have the
info program handy, use the Info reader provided within
GNU Emacs, calling ‘tar’ from the main Info menu.
There is currently no man page for GNU tar.
If you observe such a man page on the system you are running,
either it does not belong to GNU tar, or it has not
been produced by GNU. Some package maintainers convert
tar --help output to a man page, using help2man. In
any case, please bear in mind that the authoritative source of
information about GNU tar is this Texinfo documentation.
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tar default values GNU tar has some predefined defaults that are used when you do not
explicitly specify another values. To obtain a list of such
defaults, use ‘--show-defaults’ option. This will output the
values in the form of tar command line options:
tar --show-defaults --format=gnu -f- -b20 --quoting-style=escape --rmt-command=/etc/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.
The above output shows that this version of GNU tar defaults to
using ‘gnu’ archive format (see section Controlling the Archive Format), it uses standard
output as the archive, if no ‘--file’ option has been given
(see section The ‘--file’ Option), the default blocking factor is 20
(see section The Blocking Factor of an Archive). It also shows the default locations where
tar will look for rmt and rsh binaries.
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tar progress Typically, tar performs most operations without reporting any
information to the user except error messages. When using tar
with many options, particularly ones with complicated or
difficult-to-predict behavior, it is possible to make serious mistakes.
tar provides several options that make observing tar
easier. These options cause tar to print information as it
progresses in its job, and you might want to use them just for being
more careful about what is going on, or merely for entertaining
yourself. If you have encountered a problem when operating on an
archive, however, you may need more information than just an error
message in order to solve the problem. The following options can be
helpful diagnostic tools.
Normally, the ‘--list’ (‘-t’) command to list an archive
prints just the file names (one per line) and the other commands are
silent. When used with most operations, the ‘--verbose’
(‘-v’) option causes tar to print the name of each
file or archive member as it is processed. This and the other options
which make tar print status information can be useful in
monitoring tar.
With ‘--create’ or ‘--extract’, ‘--verbose’ used
once just prints the names of the files or members as they are processed.
Using it twice causes tar to print a longer listing
(See verbose member listing, for the description) for each member.
Since ‘--list’ already prints the names of the members,
‘--verbose’ used once with ‘--list’ causes tar
to print an ‘ls -l’ type listing of the files in the archive.
The following examples both extract members with long list output:
$ tar --extract --file=archive.tar --verbose --verbose $ tar xvvf archive.tar |
Verbose output appears on the standard output except when an archive is
being written to the standard output, as with ‘tar --create
--file=- --verbose’ (‘tar cfv -’, or even ‘tar cv’—if the
installer let standard output be the default archive). In that case
tar writes verbose output to the standard error stream.
If ‘--index-file=file’ is specified, tar sends
verbose output to file rather than to standard output or standard
error.
The ‘--totals’ option causes tar to print on the
standard error the total amount of bytes transferred when processing
an archive. When creating or appending to an archive, this option
prints the number of bytes written to the archive and the average
speed at which they have been written, e.g.:
$ tar -c -f archive.tar --totals /home Total bytes written: 7924664320 (7.4GiB, 85MiB/s) |
When reading an archive, this option displays the number of bytes read:
$ tar -x -f archive.tar --totals Total bytes read: 7924664320 (7.4GiB, 95MiB/s) |
Finally, when deleting from an archive, the ‘--totals’ option displays both numbers plus number of bytes removed from the archive:
$ tar --delete -f foo.tar --totals --wildcards '*~' Total bytes read: 9543680 (9.2MiB, 201MiB/s) Total bytes written: 3829760 (3.7MiB, 81MiB/s) Total bytes deleted: 1474048 |
You can also obtain this information on request. When ‘--totals’ is used with an argument, this argument is interpreted as a symbolic name of a signal, upon delivery of which the statistics is to be printed:
Print statistics upon delivery of signal signo. Valid arguments
are: SIGHUP, SIGQUIT, SIGINT, SIGUSR1 and
SIGUSR2. Shortened names without ‘SIG’ prefix are also
accepted.
Both forms of ‘--totals’ option can be used simultaneously.
Thus, tar -x --totals --totals=USR1 instructs tar to
extract all members from its default archive and print statistics
after finishing the extraction, as well as when receiving signal
SIGUSR1.
The ‘--checkpoint’ option prints an occasional message
as tar reads or writes the archive. It is designed for
those who don't need the more detailed (and voluminous) output of
‘--block-number’ (‘-R’), but do want visual confirmation
that tar is actually making forward progress. By default it
prints a message each 10 records read or written. This can be changed
by giving it a numeric argument after an equal sign:
$ tar -c --checkpoint=1000 /var tar: Write checkpoint 1000 tar: Write checkpoint 2000 tar: Write checkpoint 3000 |
This example shows the default checkpoint message used by
tar. If you place a dot immediately after the equal
sign, it will print a ‘.’ at each checkpoint(7). For example:
$ tar -c --checkpoint=.1000 /var ... |
The ‘--checkpoint’ option provides a flexible mechanism for executing arbitrary actions upon hitting checkpoints, see the next section (see section Checkpoints), for more information on it.
The ‘--show-omitted-dirs’ option, when reading an archive—with ‘--list’ or ‘--extract’, for example—causes a message to be printed for each directory in the archive which is skipped. This happens regardless of the reason for skipping: the directory might not have been named on the command line (implicitly or explicitly), it might be excluded by the use of the ‘--exclude=pattern’ option, or some other reason.
If ‘--block-number’ (‘-R’) is used, tar prints, along with
every message it would normally produce, the block number within the
archive where the message was triggered. Also, supplementary messages
are triggered when reading blocks full of NULs, or when hitting end of
file on the archive. As of now, if the archive is properly terminated
with a NUL block, the reading of the file may stop before end of file
is met, so the position of end of file will not usually show when
‘--block-number’ (‘-R’) is used. Note that GNU tar
drains the archive before exiting when reading the
archive from a pipe.
This option is especially useful when reading damaged archives, since it helps pinpoint the damaged sections. It can also be used with ‘--list’ (‘-t’) when listing a file-system backup tape, allowing you to choose among several backup tapes when retrieving a file later, in favor of the tape where the file appears earliest (closest to the front of the tape). See section Backup options.
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A checkpoint is a moment of time before writing nth record to the archive (a write checkpoint), or before reading nth record from the archive (a read checkpoint). Checkpoints allow to periodically execute arbitrary actions.
The checkpoint facility is enabled using the following option:
Schedule checkpoints before writing or reading each nth record. The default value for n is 10.
A list of arbitrary actions can be executed at each checkpoint. These actions include: pausing, displaying textual messages, and executing arbitrary external programs. Actions are defined using the ‘--checkpoint-action’ option.
Execute an action at each checkpoint.
The simplest value of action is ‘echo’. It instructs
tar to display the default message on the standard error
stream upon arriving at each checkpoint. The default message is (in
POSIX locale) ‘Write checkpoint n’, for write
checkpoints, and ‘Read checkpoint n’, for read checkpoints.
Here, n represents ordinal number of the checkpoint.
In another locales, translated versions of this message are used.
This is the default action, so running:
$ tar -c --checkpoint=1000 --checkpoint-action=echo /var |
is equivalent to:
$ tar -c --checkpoint=1000 /var |
The ‘echo’ action also allows to supply a customized message. You do so by placing an equals sign and the message right after it, e.g.:
--checkpoint-action="echo=Hit %s checkpoint #%u" |
The ‘%s’ and ‘%u’ in the above example are meta-characters. The ‘%s’ meta-character is replaced with the type of the checkpoint: ‘write’ or ‘read’ (or a corresponding translated version in locales other than POSIX). The ‘%u’ meta-character is replaced with the ordinal number of the checkpoint. Thus, the above example could produce the following output when used with the ‘--create’ option:
tar: Hit write checkpoint #10 tar: Hit write checkpoint #20 tar: Hit write checkpoint #30 |
Aside from meta-character expansion, the message string is subject to unquoting, during which the backslash escape sequences are replaced with their corresponding ASCII characters (see escape sequences). E.g. the following action will produce an audible bell and the message described above at each checkpoint:
--checkpoint-action='echo=\aHit %s checkpoint #%u' |
There is also a special action which produces an audible signal: ‘bell’. It is not equivalent to ‘echo='\a'’, because ‘bell’ sends the bell directly to the console (‘/dev/tty’), whereas ‘echo='\a'’ sends it to the standard error.
The ‘ttyout=string’ action outputs string to
‘/dev/tty’, so it can be used even if the standard output is
redirected elsewhere. The string is subject to the same
modifications as with ‘echo’ action. In contrast to the latter,
‘ttyout’ does not prepend tar executable name to the
string, nor does it output a newline after it. For example, the
following action will print the checkpoint message at the same screen
line, overwriting any previous message:
--checkpoint-action="ttyout=\rHit %s checkpoint #%u" |
Another available checkpoint action is ‘dot’ (or ‘.’). It
instructs tar to print a single dot on the standard listing
stream, e.g.:
$ tar -c --checkpoint=1000 --checkpoint-action=dot /var ... |
For compatibility with previous GNU tar versions, this action can
be abbreviated by placing a dot in front of the checkpoint frequency,
as shown in the previous section.
Yet another action, ‘sleep’, pauses tar for a specified
amount of seconds. The following example will stop for 30 seconds at each
checkpoint:
$ tar -c --checkpoint=1000 --checkpoint-action=sleep=30 |
Finally, the exec action executes a given external program.
For example:
$ tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint |
This program is executed using /bin/sh -c, with no
additional arguments. Its exit code is ignored. It gets a copy of
tar's environment plus the following variables:
TAR_VERSIONGNU tar version number.
TAR_ARCHIVEThe name of the archive tar is processing.
TAR_BLOCKING_FACTORCurrent blocking factor (see section Blocking).
TAR_CHECKPOINTNumber of the checkpoint.
TAR_SUBCOMMANDA short option describing the operation tar is executing.
See section The Five Advanced tar Operations, for a complete list of subcommand options.
TAR_FORMATFormat of the archive being processed. See section Controlling the Archive Format, for a complete list of archive format names.
Any number of actions can be defined, by supplying several ‘--checkpoint-action’ options in the command line. For example, the command below displays two messages, pauses execution for 30 seconds and executes the ‘/sbin/cpoint’ script:
$ tar -c -f arc.tar \
--checkpoint-action='\aecho=Hit %s checkpoint #%u' \
--checkpoint-action='echo=Sleeping for 30 seconds' \
--checkpoint-action='sleep=30' \
--checkpoint-action='exec=/sbin/cpoint'
|
This example also illustrates the fact that ‘--checkpoint-action’ can be used without ‘--checkpoint’. In this case, the default checkpoint frequency (at each 10th record) is assumed.
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Typically, tar carries out a command without stopping for
further instructions. In some situations however, you may want to
exclude some files and archive members from the operation (for instance
if disk or storage space is tight). You can do this by excluding
certain files automatically (see section Choosing Files and Names for tar), or by performing
an operation interactively, using the ‘--interactive’ (‘-w’) option.
tar also accepts ‘--confirmation’ for this option.
When the ‘--interactive’ (‘-w’) option is specified, before
reading, writing, or deleting files, tar first prints a message
for each such file, telling what operation it intends to take, then asks
for confirmation on the terminal. The actions which require
confirmation include adding a file to the archive, extracting a file
from the archive, deleting a file from the archive, and deleting a file
from disk. To confirm the action, you must type a line of input
beginning with ‘y’. If your input line begins with anything other
than ‘y’, tar skips that file.
If tar is reading the archive from the standard input,
tar opens the file ‘/dev/tty’ to support the interactive
communications.
Verbose output is normally sent to standard output, separate from
other error messages. However, if the archive is produced directly
on standard output, then verbose output is mixed with errors on
stderr. Producing the archive on standard output may be used
as a way to avoid using disk space, when the archive is soon to be
consumed by another process reading it, say. Some people felt the need
of producing an archive on stdout, still willing to segregate between
verbose output and error output. A possible approach would be using a
named pipe to receive the archive, and having the consumer process to
read from that named pipe. This has the advantage of letting standard
output free to receive verbose output, all separate from errors.
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tar Operations | [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
tar Operations The basic tar operations, ‘--create’ (‘-c’),
‘--list’ (‘-t’) and ‘--extract’ (‘--get’,
‘-x’), are currently presented and described in the tutorial
chapter of this manual. This section provides some complementary notes
for these operations.
Creating an empty archive would have some kind of elegance. One can
initialize an empty archive and later use ‘--append’
(‘-r’) for adding all members. Some applications would not
welcome making an exception in the way of adding the first archive
member. On the other hand, many people reported that it is
dangerously too easy for tar to destroy a magnetic tape with
an empty archive(8). The two most common errors are:
create instead of extract, when the
intent was to extract the full contents of an archive. This error
is likely: keys c and x are right next to each other on
the QWERTY keyboard. Instead of being unpacked, the archive then
gets wholly destroyed. When users speak about exploding an
archive, they usually mean something else :-).
file, when the intent was to create
an archive with a single file in it. This error is likely because a
tired user can easily add the f key to the cluster of option
letters, by the mere force of habit, without realizing the full
consequence of doing so. The usual consequence is that the single
file, which was meant to be saved, is rather destroyed.
So, recognizing the likelihood and the catastrophic nature of these
errors, GNU tar now takes some distance from elegance, and
cowardly refuses to create an archive when ‘--create’ option is
given, there are no arguments besides options, and
‘--files-from’ (‘-T’) option is not used. To get
around the cautiousness of GNU tar and nevertheless create an
archive with nothing in it, one may still use, as the value for the
‘--files-from’ option, a file with no names in it, as shown in
the following commands:
tar --create --file=empty-archive.tar --files-from=/dev/null tar cfT empty-archive.tar /dev/null |
A socket is stored, within a GNU tar archive, as a pipe.
GNU tar now shows dates as ‘1996-08-30’,
while it used to show them as ‘Aug 30 1996’. Preferably,
people should get used to ISO 8601 dates. Local American dates should
be made available again with full date localization support, once
ready. In the meantime, programs not being localizable for dates
should prefer international dates, that's really the way to go.
Look up http://www.cl.cam.ac.uk/~mgk25/iso-time.html if you are curious, it contains a detailed explanation of the ISO 8601 standard.
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tar Operations Now that you have learned the basics of using GNU tar, you may want
to learn about further ways in which tar can help you.
This chapter presents five, more advanced operations which you probably
won't use on a daily basis, but which serve more specialized functions.
We also explain the different styles of options and why you might want
to use one or another, or a combination of them in your tar
commands. Additionally, this chapter includes options which allow you to
define the output from tar more carefully, and provide help and
error correction in special circumstances.
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tar Operations (This message will disappear, once this node revised.)
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’, ‘rock’, 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:
Add new entries to an archive that already exists.
Add more recent copies of archive members to the end of an archive, if they exist.
Add one or more pre-existing archives to the end of another archive.
Delete items from an archive (does not work on tapes).
Compare archive members to their counterparts in the file system.
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(This message will disappear, once this node revised.)
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 section 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 four
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 this(9). 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 section —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.)
| 4.2.2.1 Appending Files to an Archive | ||
| 4.2.2.2 Multiple Members with the Same Name |
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(This message will disappear, once this node revised.)
The simplest way to add a file to an already existing archive is the ‘--append’ (‘-r’) operation, which writes specified files into the archive whether or not they are already among the archived files.
When you use ‘--append’, you must specify file name arguments, as there is no default. If you specify a file that already exists in the archive, another copy of the file will be added to the end of the archive. As with other operations, the member names of the newly added files will be exactly the same as their names given on the command line. The ‘--verbose’ (‘-v’) option will print out the names of the files as they are written into the archive.
‘--append’ cannot be performed on some tape drives, unfortunately,
due to deficiencies in the formats those tape drives use. The archive
must be a valid tar archive, or else the results of using this
operation will be unpredictable. See section Tapes and Other Archive Media.
To demonstrate using ‘--append’ to add a file to an archive,
create a file called ‘rock’ in the ‘practice’ directory.
Make sure you are in the ‘practice’ directory. Then, run the
following tar command to add ‘rock’ to
‘collection.tar’:
$ tar --append --file=collection.tar rock |
If you now use the ‘--list’ (‘-t’) operation, you will see that ‘rock’ has been added to the archive:
$ 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 |
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You can use ‘--append’ (‘-r’) to add copies of files
which have been updated since the archive was created. (However, we
do not recommend doing this since there is another tar
option called ‘--update’; See section Updating an Archive, for more information.
We describe this use of ‘--append’ here for the sake of
completeness.) When you extract the archive, the older version will
be effectively lost. This works because files are extracted from an
archive in the order in which they were archived. Thus, when the
archive is extracted, a file archived later in time will replace a
file of the same name which was archived earlier, even though the
older version of the file will remain in the archive unless you delete
all versions of the file.
Supposing you change the file ‘blues’ and then append the changed version to ‘collection.tar’. As you saw above, the original ‘blues’ is in the archive ‘collection.tar’. If you change the file and append the new version of the file to the archive, there will be two copies in the archive. When you extract the archive, the older version of the file will be extracted first, and then replaced by the newer version when it is extracted.
You can append the new, changed copy of the file ‘blues’ to the archive in this way:
$ tar --append --verbose --file=collection.tar blues blues |
Because you specified the ‘--verbose’ option, tar has
printed the name of the file being appended as it was acted on. Now
list the contents of the archive:
$ 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 |
The newest version of ‘blues’ is now at the end of the archive (note the different creation dates and file sizes). If you extract the archive, the older version of the file ‘blues’ will be replaced by the newer version. You can confirm this by extracting the archive and running ‘ls’ on the directory.
If you wish to extract the first occurrence of the file ‘blues’ from the archive, use ‘--occurrence’ option, as shown in the following example:
$ tar --extract -vv --occurrence --file=collection.tar blues -rw-r--r-- me user 21 1996-09-23 16:44 blues |
See section Changing How tar Writes Files, for more information on ‘--extract’ and
See section –occurrence, for the description of
‘--occurrence’ option.
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(This message will disappear, once this node revised.)
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 section Multiple Members with the Same Name, for a detailed discussion.
| 4.2.3.1 How to Update an Archive Using ‘--update’ |
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You must use file name arguments with the ‘--update’
(‘-u’) operation. If you don't specify any files,
tar won't act on any files and won't tell you that it didn't
do anything (which may end up confusing you).
To see the ‘--update’ option at work, create a new file,
‘classical’, in your practice directory, and some extra text to the
file ‘blues’, using any text editor. Then invoke tar with
the ‘update’ operation and the ‘--verbose’ (‘-v’)
option specified, using the names of all the files in the practice
directory as file name arguments:
$ tar --update -v -f collection.tar blues folk rock classical blues classical $ |
Because we have specified verbose mode, tar prints out the names
of the files it is working on, which in this case are the names of the
files that needed to be updated. If you run ‘tar --list’ and look
at the archive, you will see ‘blues’ and ‘classical’ at its
end. There will be a total of two versions of the member ‘blues’;
the one at the end will be newer and larger, since you added text before
updating it.
(The reason tar does not overwrite the older file when updating
it is because writing to the middle of a section of tape is a difficult
process. Tapes are not designed to go backward. See section Tapes and Other Archive Media, for more
information about tapes.
‘--update’ (‘-u’) is not suitable for performing backups for two
reasons: it does not change directory content entries, and it
lengthens the archive every time it is used. The GNU tar
options intended specifically for backups are more
efficient. If you need to run backups, please consult Performing Backups and Restoring Files.
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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 one.
(10)
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:
$ cd .. $ 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 section Ignoring Blocks of Zeros, for further
information on dealing with archives improperly combined using the
cat shell utility.
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(This message will disappear, once this node revised.)
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 section 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.
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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 later goal, See section Verifying Data as It is Stored.
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The previous chapter described the basics of how to use ‘--create’ (‘-c’) to create an archive from a set of files. See section How to Create Archives. This section described advanced options to be used with ‘--create’.
| 4.3.1 Overriding File Metadata | ||
| 4.3.2 Ignore Fail Read |
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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.
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 Permissions: (fileutils)File permissions section `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' . |
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 section Date input formats) or a name of the 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 UTC, January 1, 1970:
$ tar -c -f archive.tar --mtime='1970-01-01' . |
When used with ‘--verbose’ (see section 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 … |
Specifies that tar should use user as the owner of members
when creating archives, instead of the user associated with the source
file. The argument user can be either an existing user symbolic
name, or a decimal numeric user ID.
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 .
|
Files added to the tar archive will have a group ID of group,
rather than the group from the source file. The argument group
can be either an existing group symbolic name, or a decimal numeric group ID.
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Do not exit with nonzero on unreadable files or directories.
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The previous chapter showed how to use ‘--extract’ to extract
an archive into the file system. Various options cause tar to
extract more information than just file contents, such as the owner,
the permissions, the modification date, and so forth. This section
presents options to be used with ‘--extract’ when certain special
considerations arise. You may review the information presented in
How to Extract Members from an Archive for more basic information about the
‘--extract’ operation.
| 4.4.1 Options to Help Read Archives | ||
4.4.2 Changing How tar Writes Files | ||
| 4.4.3 Coping with Scarce Resources |
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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 section 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 section The Blocking Factor of an Archive.
| Reading Full Records | ||
| Ignoring Blocks of Zeros |
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Use in conjunction with ‘--extract’ (‘--get’, ‘-x’) to read an archive which contains incomplete records, or one which has a blocking factor less than the one specified.
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Normally, tar stops reading when it encounters a block of zeros
between file entries (which usually indicates the end of the archive).
‘--ignore-zeros’ (‘-i’) allows tar to
completely read an archive which contains a block of zeros before the
end (i.e., a damaged archive, or one that was created by concatenating
several archives together).
The ‘--ignore-zeros’ (‘-i’) option is turned off by default because many
versions of tar write garbage after the end-of-archive entry,
since that part of the media is never supposed to be read. GNU tar
does not write after the end of an archive, but seeks to
maintain compatibility among archiving utilities.
To ignore blocks of zeros (i.e., end-of-archive entries) which may be encountered while reading an archive. Use in conjunction with ‘--extract’ or ‘--list’.
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tar Writes Files (This message will disappear, once this node revised.)
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When extracting files, if tar discovers that the extracted
file already exists, it normally replaces the file by removing it before
extracting it, to prevent confusion in the presence of hard or symbolic
links. (If the existing file is a symbolic link, it is removed, not
followed.) However, if a directory cannot be removed because it is
nonempty, tar normally overwrites its metadata (ownership,
permission, etc.). The ‘--overwrite-dir’ option enables this
default behavior. To be more cautious and preserve the metadata of
such a directory, use the ‘--no-overwrite-dir’ option.
To be even more cautious and prevent existing files from being replaced, use
the ‘--keep-old-files’ (‘-k’) option. It causes tar to refuse
to replace or update a file that already exists, i.e., a file with the
same name as an archive member prevents extraction of that archive
member. Instead, it reports an error.
To be more aggressive about altering existing files, use the
‘--overwrite’ option. It causes tar to overwrite
existing files and to follow existing symbolic links when extracting.
Some people argue that GNU tar should not hesitate
to overwrite files with other files when extracting. When extracting
a tar archive, they expect to see a faithful copy of the
state of the file system when the archive was created. It is debatable
that this would always be a proper behavior. For example, suppose one
has an archive in which ‘usr/local’ is a link to
‘usr/local2’. Since then, maybe the site removed the link and
renamed the whole hierarchy from ‘/usr/local2’ to
‘/usr/local’. Such things happen all the time. I guess it would
not be welcome at all that GNU tar removes the
whole hierarchy just to make room for the link to be reinstated
(unless it also simultaneously restores the full
‘/usr/local2’, of course!) GNU tar is indeed
able to remove a whole hierarchy to reestablish a symbolic link, for
example, but only if ‘--recursive-unlink’ is specified
to allow this behavior. In any case, single files are silently
removed.
Finally, the ‘--unlink-first’ (‘-U’) option can improve performance in
some cases by causing tar to remove files unconditionally
before extracting them.
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Overwrite existing files and directory metadata when extracting files from an archive.
This causes tar to write extracted files into the file system without
regard to the files already on the system; i.e., files with the same
names as archive members are overwritten when the archive is extracted.
It also causes tar to extract the ownership, permissions,
and time stamps onto any preexisting files or directories.
If the name of a corresponding file name is a symbolic link, the file
pointed to by the symbolic link will be overwritten instead of the
symbolic link itself (if this is possible). Moreover, special devices,
empty directories and even symbolic links are automatically removed if
they are in the way of extraction.
Be careful when using the ‘--overwrite’ option, particularly when combined with the ‘--absolute-names’ (‘-P’) option, as this combination can change the contents, ownership or permissions of any file on your system. Also, many systems do not take kindly to overwriting files that are currently being executed.
Overwrite the metadata of directories when extracting files from an archive, but remove other files before extracting.
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Do not replace existing files from archive. The
‘--keep-old-files’ (‘-k’) option prevents tar
from replacing existing files with files with the same name from the
archive. The ‘--keep-old-files’ option is meaningless with
‘--list’ (‘-t’). Prevents tar from replacing
files in the file system during extraction.
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Do not replace existing files that are newer than their archive copies. This option is meaningless with ‘--list’ (‘-t’).
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Remove files before extracting over them.
This can make tar run a bit faster if you know in advance
that the extracted files all need to be removed. Normally this option
slows tar down slightly, so it is disabled by default.
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When this option is specified, try removing files and directory hierarchies before extracting over them. This is a dangerous option!
If you specify the ‘--recursive-unlink’ option,
tar removes anything that keeps you from extracting a file
as far as current permissions will allow it. This could include removal
of the contents of a full directory hierarchy.
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Normally, tar sets the data modification times of extracted
files to the corresponding times recorded for the files in the archive, but
limits the permissions of extracted files by the current umask
setting.
To set the data modification times of extracted files to the time when the files were extracted, use the ‘--touch’ (‘-m’) option in conjunction with ‘--extract’ (‘--get’, ‘-x’).
Sets the data modification time of extracted archive members to the time they were extracted, not the time recorded for them in the archive. Use in conjunction with ‘--extract’ (‘--get’, ‘-x’).
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To set the modes (access permissions) of extracted files to those recorded for those files in the archive, use ‘--same-permissions’ in conjunction with the ‘--extract’ (‘--get’, ‘-x’) operation.
Set modes of extracted archive members to those recorded in the archive, instead of current umask settings. Use in conjunction with ‘--extract’ (‘--get’, ‘-x’).
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After successfully extracting a file member, GNU tar normally
restores its permissions and modification times, as described in the
previous sections. This cannot be done for directories, because
after extracting a directory tar will almost certainly
extract files into that directory and this will cause the directory
modification time to be updated. Moreover, restoring that directory
permissions may not permit file creation within it. Thus, restoring
directory permissions and modification times must be delayed at least
until all files have been extracted into that directory. GNU tar
restores directories using the following approach.
The extracted directories are created with the mode specified in the
archive, as modified by the umask of the user, which gives sufficient
permissions to allow file creation. The meta-information about the
directory is recorded in the temporary list of directories. When
preparing to extract next archive member, GNU tar checks if the
directory prefix of this file contains the remembered directory. If
it does not, the program assumes that all files have been extracted
into that directory, restores its modification time and permissions
and removes its entry from the internal list. This approach allows
to correctly restore directory meta-information in the majority of
cases, while keeping memory requirements sufficiently small. It is
based on the fact, that most tar archives use the predefined
order of members: first the directory, then all the files and
subdirectories in that directory.
However, this is not always true. The most important exception are
incremental archives (see section Using tar to Perform Incremental Dumps). The member order in
an incremental archive is reversed: first all directory members are
stored, followed by other (non-directory) members. So, when extracting
from incremental archives, GNU tar alters the above procedure. It
remembers all restored directories, and restores their meta-data
only after the entire archive has been processed. Notice, that you do
not need to specify any special options for that, as GNU tar
automatically detects archives in incremental format.
There may be cases, when such processing is required for normal archives too. Consider the following example:
$ tar --no-recursion -cvf archive \
foo foo/file1 bar bar/file foo/file2
foo/
foo/file1
bar/
bar/file
foo/file2
|
During the normal operation, after encountering ‘bar’
GNU tar will assume that all files from the directory ‘foo’
were already extracted and will therefore restore its timestamp and
permission bits. However, after extracting ‘foo/file2’ the
directory timestamp will be offset again.
To correctly restore directory meta-information in such cases, use ‘delay-directory-restore’ command line option:
Delays restoring of the modification times and permissions of extracted directories until the end of extraction. This way, correct meta-information is restored even if the archive has unusual member ordering.
Cancel the effect of the previous ‘--delay-directory-restore’.
Use this option if you have used ‘--delay-directory-restore’ in
TAR_OPTIONS variable (see TAR_OPTIONS) and wish to
temporarily disable it.
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To write the extracted files to the standard output, instead of creating the files on the file system, use ‘--to-stdout’ (‘-O’) in conjunction with ‘--extract’ (‘--get’, ‘-x’). This option is useful if you are extracting files to send them through a pipe, and do not need to preserve them in the file system. If you extract multiple members, they appear on standard output concatenated, in the order they are found in the archive.
Writes files to the standard output. Use only in conjunction with
‘--extract’ (‘--get’, ‘-x’). When this option is
used, instead of creating the files specified, tar writes
the contents of the files extracted to its standard output. This may
be useful if you are only extracting the files in order to send them
through a pipe. This option is meaningless with ‘--list’
(‘-t’).
This can be useful, for example, if you have a tar archive containing a big file and don't want to store the file on disk before processing it. You can use a command like this:
tar -xOzf foo.tgz bigfile | process |
or even like this if you want to process the concatenation of the files:
tar -xOzf foo.tgz bigfile1 bigfile2 | process |
However, ‘--to-command’ may be more convenient for use with multiple files. See the next section.
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You can instruct tar to send the contents of each extracted
file to the standard input of an external program:
Extract files and pipe their contents to the standard input of
command. When this option is used, instead of creating the
files specified, tar invokes command and pipes the
contents of the files to its standard output. Command may
contain command line arguments. The program is executed via
sh -c. Notice, that command is executed once for each regular file
extracted. Non-regular files (directories, etc.) are ignored when this
option is used.
The command can obtain the information about the file it processes from the following environment variables:
TAR_FILETYPEType of the file. It is a single letter with the following meaning:
f | Regular file |
d | Directory |
l | Symbolic link |
h | Hard link |
b | Block device |
c | Character device |
Currently only regular files are supported.
TAR_MODEFile mode, an octal number.
TAR_FILENAMEThe name of the file.
TAR_REALNAMEName of the file as stored in the archive.
TAR_UNAMEName of the file owner.
TAR_GNAMEName of the file owner group.
TAR_ATIMETime of last access. It is a decimal number, representing seconds since the epoch. If the archive provides times with nanosecond precision, the nanoseconds are appended to the timestamp after a decimal point.
TAR_MTIMETime of last modification.
TAR_CTIMETime of last status change.
TAR_SIZESize of the file.
TAR_UIDUID of the file owner.
TAR_GIDGID of the file owner.
In addition to these variables, TAR_VERSION contains the
GNU tar version number.
If command exits with a non-0 status, tar will print
an error message similar to the following:
tar: 2345: Child returned status 1 |
Here, ‘2345’ is the PID of the finished process.
If this behavior is not wanted, use ‘--ignore-command-error’:
Ignore exit codes of subprocesses. Notice that if the program exits on signal or otherwise terminates abnormally, the error message will be printed even if this option is used.
Cancel the effect of any previous ‘--ignore-command-error’
option. This option is useful if you have set
‘--ignore-command-error’ in TAR_OPTIONS
(see TAR_OPTIONS) and wish to temporarily cancel it.
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Remove files after adding them to the archive.
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| Starting File | ||
| Same Order |
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Starts an operation in the middle of an archive. Use in conjunction with ‘--extract’ (‘--get’, ‘-x’) or ‘--list’ (‘-t’).
If a previous attempt to extract files failed due to lack of disk
space, you can use ‘--starting-file=name’ (‘-K
name’) to start extracting only after member name of the
archive. This assumes, of course, that there is now free space, or
that you are now extracting into a different file system. (You could
also choose to suspend tar, remove unnecessary files from
the file system, and then restart the same tar operation.
In this case, ‘--starting-file’ is not necessary.
See section Using tar to Perform Incremental Dumps, See section Asking for Confirmation During Operations, and Excluding Some Files.)
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To process large lists of file names on machines with small amounts of memory. Use in conjunction with ‘--compare’ (‘--diff’, ‘-d’), ‘--list’ (‘-t’) or ‘--extract’ (‘--get’, ‘-x’).
The ‘--same-order’ (‘--preserve-order’, ‘-s’) option tells tar that the list of file
names to be listed or extracted is sorted in the same order as the
files in the archive. This allows a large list of names to be used,
even on a small machine that would not otherwise be able to hold all
the names in memory at the same time. Such a sorted list can easily be
created by running ‘tar -t’ on the archive and editing its output.
This option is probably never needed on modern computer systems.
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GNU tar offers options for making backups of files
before writing new versions. These options control the details of
these backups. They may apply to the archive itself before it is
created or rewritten, as well as individual extracted members. Other
GNU programs (cp, install, ln,
and mv, for example) offer similar options.
Backup options may prove unexpectedly useful when extracting archives containing many members having identical name, or when extracting archives on systems having file name limitations, making different members appear as having similar names through the side-effect of name truncation.
When any existing file is backed up before being overwritten by extraction, then clashing files are automatically be renamed to be unique, and the true name is kept for only the last file of a series of clashing files. By using verbose mode, users may track exactly what happens.
At the detail level, some decisions are still experimental, and may change in the future, we are waiting comments from our users. So, please do not learn to depend blindly on the details of the backup features. For example, currently, directories themselves are never renamed through using these options, so, extracting a file over a directory still has good chances to fail. Also, backup options apply to created archives, not only to extracted members. For created archives, backups will not be attempted when the archive is a block or character device, or when it refers to a remote file.
For the sake of simplicity and efficiency, backups are made by renaming old files prior to creation or extraction, and not by copying. The original name is restored if the file creation fails. If a failure occurs after a partial extraction of a file, both the backup and the partially extracted file are kept.
Back up files that are about to be overwritten or removed. Without this option, the original versions are destroyed.
Use method to determine the type of backups made.
If method is not specified, use the value of the VERSION_CONTROL
environment variable. And if VERSION_CONTROL is not set,
use the ‘existing’ method.
This option corresponds to the Emacs variable ‘version-control’; the same values for method are accepted as in Emacs. This option also allows more descriptive names. The valid methods are:
Always make numbered backups.
Make numbered backups of files that already have them, simple backups of the others.
Always make simple backups.
Append suffix to each backup file made with ‘--backup’. If this
option is not specified, the value of the SIMPLE_BACKUP_SUFFIX
environment variable is used. And if SIMPLE_BACKUP_SUFFIX is not
set, the default is ‘~’, just as in Emacs.
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tar Usages (This message will disappear, once this node revised.)
You can easily use archive files to transport a group of files from
one system to another: put all relevant files into an archive on one
computer system, transfer the archive to another system, and extract
the contents there. The basic transfer medium might be magnetic tape,
Internet FTP, or even electronic mail (though you must encode the
archive with uuencode in order to transport it properly by
mail). Both machines do not have to use the same operating system, as
long as they both support the tar program.
For example, here is how you might copy a directory's contents from one disk to another, while preserving the dates, modes, owners and link-structure of all the files therein. In this case, the transfer medium is a pipe, which is one a Unix redirection mechanism:
$ (cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -) |
You can avoid subshells by using ‘-C’ option:
$ tar -C sourcedir -cf - . | tar -C targetdir -xf - |
The command also works using short option forms:
$ (cd sourcedir; tar --create --file=- . ) \
| (cd targetdir; tar --extract --file=-)
# Or:
$ tar --directory sourcedir --create --file=- . ) \
| tar --directory targetdir --extract --file=-
|
This is one of the easiest methods to transfer a tar archive.
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You have now seen how to use all eight of the operations available to
tar, and a number of the possible options. The next chapter
explains how to choose and change file and archive names, how to use
files to store names of other files which you can then call as
arguments to tar (this can help you save time if you expect to
archive the same list of files a number of times), and so forth.
If there are too many files to conveniently list on the command line,
you can list the names in a file, and tar will read that file.
See section Reading Names from a File.
There are various ways of causing tar to skip over some files,
and not archive them. See section Choosing Files and Names for tar.
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(This message will disappear, once this node revised.)
GNU tar is distributed along with the scripts
which the Free Software Foundation uses for performing backups. There
is no corresponding scripts available yet for doing restoration of
files. Even if there is a good chance those scripts may be satisfying
to you, they are not the only scripts or methods available for doing
backups and restore. You may well create your own, or use more
sophisticated packages dedicated to that purpose.
Some users are enthusiastic about Amanda (The Advanced Maryland
Automatic Network Disk Archiver), a backup system developed by James
da Silva ‘jds@cs.umd.edu’ and available on many Unix systems.
This is free software, and it is available at these places:
http://www.cs.umd.edu/projects/amanda/amanda.html ftp://ftp.cs.umd.edu/pub/amanda |
This chapter documents both the provided shell scripts and tar
options which are more specific to usage as a backup tool.
To back up a file system means to create archives that contain all the files in that file system. Those archives can then be used to restore any or all of those files (for instance if a disk crashes or a file is accidentally deleted). File system backups are also called dumps.
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tar to Perform Full Dumps (This message will disappear, once this node revised.)
Full dumps should only be made when no other people or programs
are modifying files in the file system. If files are modified while
tar is making the backup, they may not be stored properly in
the archive, in which case you won't be able to restore them if you
have to. (Files not being modified are written with no trouble, and do
not corrupt the entire archive.)
You will want to use the ‘--label=archive-label’ (‘-V archive-label’) option to give the archive a volume label, so you can tell what this archive is even if the label falls off the tape, or anything like that.
Unless the file system you are dumping is guaranteed to fit on one volume, you will need to use the ‘--multi-volume’ (‘-M’) option. Make sure you have enough tapes on hand to complete the backup.
If you want to dump each file system separately you will need to use
the ‘--one-file-system’ option to prevent
tar from crossing file system boundaries when storing
(sub)directories.
The ‘--incremental’ (‘-G’) (see section Using tar to Perform Incremental Dumps)
option is not needed, since this is a complete copy of everything in
the file system, and a full restore from this backup would only be
done onto a completely
empty disk.
Unless you are in a hurry, and trust the tar program (and your
tapes), it is a good idea to use the ‘--verify’ (‘-W’)
option, to make sure your files really made it onto the dump properly.
This will also detect cases where the file was modified while (or just
after) it was being archived. Not all media (notably cartridge tapes)
are capable of being verified, unfortunately.
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tar to Perform Incremental Dumps Incremental backup is a special form of GNU tar archive that
stores additional metadata so that exact state of the file system
can be restored when extracting the archive.
GNU tar currently offers two options for handling incremental
backups: ‘--listed-incremental=snapshot-file’ (‘-g
snapshot-file’) and ‘--incremental’ (‘-G’).
The option ‘--listed-incremental’ instructs tar to operate on an incremental archive with additional metadata stored in a standalone file, called a snapshot file. The purpose of this file is to help determine which files have been changed, added or deleted since the last backup, so that the next incremental backup will contain only modified files. The name of the snapshot file is given as an argument to the option:
Handle incremental backups with snapshot data in file.
To create an incremental backup, you would use ‘--listed-incremental’ together with ‘--create’ (see section How to Create Archives). For example:
$ tar --create \
--file=archive.1.tar \
--listed-incremental=/var/log/usr.snar \
/usr
|
This will create in ‘archive.1.tar’ an incremental backup of the ‘/usr’ file system, storing additional metadata in the file ‘/var/log/usr.snar’. If this file does not exist, it will be created. The created archive will then be a level 0 backup; please see the next section for more on backup levels.
Otherwise, if the file ‘/var/log/usr.snar’ exists, it determines which files are modified. In this case only these files will be stored in the archive. Suppose, for example, that after running the above command, you delete file ‘/usr/doc/old’ and create directory ‘/usr/local/db’ with the following contents:
$ ls /usr/local/db /usr/local/db/data /usr/local/db/index |
Some time later you create another incremental backup. You will then see:
$ tar --create \
--file=archive.2.tar \
--listed-incremental=/var/log/usr.snar \
/usr
tar: usr/local/db: Directory is new
usr/local/db/
usr/local/db/data
usr/local/db/index
|
The created archive ‘archive.2.tar’ will contain only these
three members. This archive is called a level 1 backup. Notice
that ‘/var/log/usr.snar’ will be updated with the new data, so if
you plan to create more ‘level 1’ backups, it is necessary to
create a working copy of the snapshot file before running
tar. The above example will then be modified as follows:
$ cp /var/log/usr.snar /var/log/usr.snar-1
$ tar --create \
--file=archive.2.tar \
--listed-incremental=/var/log/usr.snar-1 \
/usr
|
Incremental dumps depend crucially on time stamps, so the results are unreliable if you modify a file's time stamps during dumping (e.g., with the ‘--atime-preserve=replace’ option), or if you set the clock backwards.
Metadata stored in snapshot files include device numbers, which, obviously are supposed to be a non-volatile values. However, it turns out that NFS devices have undependable values when an automounter gets in the picture. This can lead to a great deal of spurious redumping in incremental dumps, so it is somewhat useless to compare two NFS devices numbers over time. The solution implemented currently is to considers all NFS devices as being equal when it comes to comparing directories; this is fairly gross, but there does not seem to be a better way to go.
Apart from using NFS, there are a number of cases where relying on device numbers can cause spurious redumping of unmodified files. For example, this occurs when archiving LVM snapshot volumes. To avoid this, use ‘--no-check-device’ option:
Do not rely on device numbers when preparing a list of changed files for an incremental dump.
Use device numbers when preparing a list of changed files
for an incremental dump. This is the default behavior. The purpose
of this option is to undo the effect of the ‘--no-check-device’
if it was given in TAR_OPTIONS environment variable
(see TAR_OPTIONS).
There is also another way to cope with changing device numbers. It is described in detail in Fixing Snapshot Files.
Note that incremental archives use tar extensions and may
not be readable by non-GNU versions of the tar program.
To extract from the incremental dumps, use
‘--listed-incremental’ together with ‘--extract’
option (see section Extracting Specific Files). In this case, tar does
not need to access snapshot file, since all the data necessary for
extraction are stored in the archive itself. So, when extracting, you
can give whatever argument to ‘--listed-incremental’, the usual
practice is to use ‘--listed-incremental=/dev/null’.
Alternatively, you can use ‘--incremental’, which needs no
arguments. In general, ‘--incremental’ (‘-G’) can be
used as a shortcut for ‘--listed-incremental’ when listing or
extracting incremental backups (for more information, regarding this
option, see incremental-op).
When extracting from the incremental backup GNU tar attempts to
restore the exact state the file system had when the archive was
created. In particular, it will delete those files in the file
system that did not exist in their directories when the archive was
created. If you have created several levels of incremental files,
then in order to restore the exact contents the file system had when
the last level was created, you will need to restore from all backups
in turn. Continuing our example, to restore the state of ‘/usr’
file system, one would do(11):
$ tar --extract \
--listed-incremental=/dev/null \
--file archive.1.tar
$ tar --extract \
--listed-incremental=/dev/null \
--file archive.2.tar
|
To list the contents of an incremental archive, use ‘--list’ (see section How to List Archives), as usual. To obtain more information about the archive, use ‘--listed-incremental’ or ‘--incremental’ combined with two ‘--verbose’ options(12):
tar --list --incremental --verbose --verbose archive.tar |
This command will print, for each directory in the archive, the list of files in that directory at the time the archive was created. This information is put out in a format which is both human-readable and unambiguous for a program: each file name is printed as
x file |
where x is a letter describing the status of the file: ‘Y’ if the file is present in the archive, ‘N’ if the file is not included in the archive, or a ‘D’ if the file is a directory (and is included in the archive). See section Dumpdir, for the detailed description of dumpdirs and status codes. Each such line is terminated by a newline character. The last line is followed by an additional newline to indicate the end of the data.
The option ‘--incremental’ (‘-G’) gives the same behavior as ‘--listed-incremental’ when used with ‘--list’ and ‘--extract’ options. When used with ‘--create’ option, it creates an incremental archive without creating snapshot file. Thus, it is impossible to create several levels of incremental backups with ‘--incremental’ option.
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An archive containing all the files in the file system is called a full backup or full dump. You could insure your data by creating a full dump every day. This strategy, however, would waste a substantial amount of archive media and user time, as unchanged files are daily re-archived.
It is more efficient to do a full dump only occasionally. To back up files between full dumps, you can use incremental dumps. A level one dump archives all the files that have changed since the last full dump.
A typical dump strategy would be to perform a full dump once a week, and a level one dump once a day. This means some versions of files will in fact be archived more than once, but this dump strategy makes it possible to restore a file system to within one day of accuracy by only extracting two archives—the last weekly (full) dump and the last daily (level one) dump. The only information lost would be in files changed or created since the last daily backup. (Doing dumps more than once a day is usually not worth the trouble).
GNU tar comes with scripts you can use to do full
and level-one (actually, even level-two and so on) dumps. Using
scripts (shell programs) to perform backups and restoration is a
convenient and reliable alternative to typing out file name lists
and tar commands by hand.
Before you use these scripts, you need to edit the file ‘backup-specs’, which specifies parameters used by the backup scripts and by the restore script. This file is usually located in ‘/etc/backup’ directory. See section Setting Parameters for Backups and Restoration, for its detailed description. Once the backup parameters are set, you can perform backups or restoration by running the appropriate script.
The name of the backup script is backup. The name of the
restore script is restore. The following sections describe
their use in detail.
Please Note: The backup and restoration scripts are
designed to be used together. While it is possible to restore files by
hand from an archive which was created using a backup script, and to create
an archive by hand which could then be extracted using the restore script,
it is easier to use the scripts. See section Using tar to Perform Incremental Dumps, before
making such an attempt.
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The file ‘backup-specs’ specifies backup parameters for the
backup and restoration scripts provided with tar. You must
edit ‘backup-specs’ to fit your system configuration and schedule
before using these scripts.
Syntactically, ‘backup-specs’ is a shell script, containing
mainly variable assignments. However, any valid shell construct
is allowed in this file. Particularly, you may wish to define
functions within that script (e.g., see RESTORE_BEGIN below).
For more information about shell script syntax, please refer to
the definition of the Shell Command Language. See also
(bashref)Top section `Bash Features' in Bash Reference Manual.
The shell variables controlling behavior of backup and
restore are described in the following subsections.
| 5.4.1 General-Purpose Variables | ||
| 5.4.2 Magnetic Tape Control | ||
| 5.4.3 User Hooks | ||
| 5.4.4 An Example Text of ‘Backup-specs’ |
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The user name of the backup administrator. Backup scripts
sends a backup report to this address.
The hour at which the backups are done. This can be a number from 0 to 23, or the time specification in form hours:minutes, or the string ‘now’.
This variable is used by backup. Its value may be overridden
using ‘--time’ option (see section Using the Backup Scripts).
The device tar writes the archive to. If TAPE_FILE
is a remote archive (see remote-dev), backup script will suppose
that your mt is able to access remote devices. If RSH
(see RSH) is set, ‘--rsh-command’ option will be added to
invocations of mt.
The blocking factor tar will use when writing the dump archive.
See section The Blocking Factor of an Archive.
A list of file systems to be dumped (for backup), or restored
(for restore). You can include any directory
name in the list — subdirectories on that file system will be
included, regardless of how they may look to other networked machines.
Subdirectories on other file systems will be ignored.
The host name specifies which host to run tar on, and should
normally be the host that actually contains the file system. However,
the host machine must have GNU tar installed, and
must be able to access the directory containing the backup scripts and
their support files using the same file name that is used on the
machine where the scripts are run (i.e., what pwd will print
when in that directory on that machine). If the host that contains
the file system does not have this capability, you can specify another
host as long as it can access the file system through NFS.
If the list of file systems is very long you may wish to put it
in a separate file. This file is usually named
‘/etc/backup/dirs’, but this name may be overridden in
‘backup-specs’ using DIRLIST variable.
The name of the file that contains a list of file systems to backup or restore. By default it is ‘/etc/backup/dirs’.
A list of individual files to be dumped (for backup), or restored
(for restore). These should be accessible from the machine on
which the backup script is run.
If the list of file systems is very long you may wish to store it
in a separate file. This file is usually named
‘/etc/backup/files’, but this name may be overridden in
‘backup-specs’ using FILELIST variable.
The name of the file that contains a list of individual files to backup or restore. By default it is ‘/etc/backup/files’.
Full file name of mt binary.
Full file name of rsh binary or its equivalent. You may wish to
set it to ssh, to improve security. In this case you will have
to use public key authentication.
Full file name of rsh binary on remote machines. This will
be passed via ‘--rsh-command’ option to the remote invocation
of GNU tar.
Name of temporary file to hold volume numbers. This needs to be accessible by all the machines which have file systems to be dumped.
Name of exclude file list. An exclude file list is a file located on the remote machine and containing the list of files to be excluded from the backup. Exclude file lists are searched in /etc/tar-backup directory. A common use for exclude file lists is to exclude files containing security-sensitive information (e.g., ‘/etc/shadow’ from backups).
This variable affects only backup.
Time to sleep between dumps of any two successive file systems
This variable affects only backup.
Script to be run when it's time to insert a new tape in for the next
volume. Administrators may want to tailor this script for their site.
If this variable isn't set, GNU tar will display its built-in
prompt, and will expect confirmation from the console. For the
description of the default prompt, see change volume prompt.
Message to display on the terminal while waiting for dump time. Usually this will just be some literal text.
Full file name of the GNU tar executable. If this is not set, backup
scripts will search tar in the current shell path.
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Backup scripts access tape device using special hook functions. These functions take a single argument – the name of the tape device. Their names are kept in the following variables:
The name of begin function. This function is called before accessing the drive. By default it retensions the tape:
MT_BEGIN=mt_begin
mt_begin() {
mt -f "$1" retension
}
|
The name of rewind function. The default definition is as follows:
MT_REWIND=mt_rewind
mt_rewind() {
mt -f "$1" rewind
}
|
The name of the function switching the tape off line. By default it is defined as follows:
MT_OFFLINE=mt_offline
mt_offline() {
mt -f "$1" offl
}
|
The name of the function used to obtain the status of the archive device, including error count. Default definition:
MT_STATUS=mt_status
mt_status() {
mt -f "$1" status
}
|
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User hooks are shell functions executed before and after
each tar invocation. Thus, there are backup
hooks, which are executed before and after dumping each file
system, and restore hooks, executed before and
after restoring a file system. Each user hook is a shell function
taking four arguments:
Its arguments are:
Current backup or restore level.
Name or IP address of the host machine being dumped or restored.
Full file name of the file system being dumped or restored.
File system name with directory separators replaced with colons. This is useful, e.g., for creating unique files.
Following variables keep the names of user hook functions
Dump begin function. It is executed before dumping the file system.
Executed after dumping the file system.
Executed before restoring the file system.
Executed after restoring the file system.
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The following is an example of ‘backup-specs’:
# site-specific parameters for file system backup. ADMINISTRATOR=friedman BACKUP_HOUR=1 TAPE_FILE=/dev/nrsmt0 # Use |
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The syntax for running a backup script is:
backup --level=level --time=time |
The ‘level’ option requests the dump level. Thus, to produce
a full dump, specify --level=0 (this is the default, so
‘--level’ may be omitted if its value is 0).
(13)
The ‘--time’ option determines when should the backup be run. Time may take three forms:
The dump must be run at hh hours mm minutes.
The dump must be run at hh hours
The dump must be run immediately.
You should start a script with a tape or disk mounted. Once you
start a script, it prompts you for new tapes or disks as it
needs them. Media volumes don't have to correspond to archive
files — a multi-volume archive can be started in the middle of a
tape that already contains the end of another multi-volume archive.
The restore script prompts for media by its archive volume,
so to avoid an error message you should keep track of which tape
(or disk) contains which volume of the archive (see section Using the Restore Script).
The backup scripts write two files on the file system. The first is a record file in ‘/etc/tar-backup/’, which is used by the scripts to store and retrieve information about which files were dumped. This file is not meant to be read by humans, and should not be deleted by them. See section Format of the Incremental Snapshot Files, for a more detailed explanation of this file.
The second file is a log file containing the names of the file systems and files dumped, what time the backup was made, and any error messages that were generated, as well as how much space was left in the media volume after the last volume of the archive was written. You should check this log file after every backup. The file name is ‘log-mm-dd-yyyy-level-n’, where mm-dd-yyyy represents current date, and n represents current dump level number.
The script also prints the name of each system being dumped to the standard output.
Following is the full list of options accepted by backup
script:
Do backup level level (default 0).
Force backup even if today's log file already exists.
Set verbosity level. The higher the level is, the more debugging information will be output during execution. Default level is 100, which means the highest debugging level.
Wait till time, then do backup.
Display short help message and exit.
Display information about the program's name, version, origin and legal status, all on standard output, and then exit successfully.
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To restore files that were archived using a scripted backup, use the
restore script. Its usage is quite straightforward. In the
simplest form, invoke restore --all, it will
then restore all the file systems and files specified in
‘backup-specs’ (see section BACKUP_DIRS).
You may select the file systems (and/or files) to restore by
giving restore list of patterns in its command
line. For example, running
restore 'albert:*' |
will restore all file systems on the machine ‘albert’. A more complicated example:
restore 'albert:*' '*:/var' |
This command will restore all file systems on the machine ‘albert’ as well as ‘/var’ file system on all machines.
By default restore will start restoring files from the lowest
available dump level (usually zero) and will continue through
all available dump levels. There may be situations where such a
thorough restore is not necessary. For example, you may wish to
restore only files from the recent level one backup. To do so,
use ‘--level’ option, as shown in the example below:
restore --level=1 |
The full list of options accepted by restore follows:
Restore all file systems and files specified in ‘backup-specs’
Start restoring from the given backup level, instead of the default 0.
Set verbosity level. The higher the level is, the more debugging information will be output during execution. Default level is 100, which means the highest debugging level.
Display short help message and exit.
Display information about the program's name, version, origin and legal status, all on standard output, and then exit successfully.
You should start the restore script with the media containing the first volume of the archive mounted. The script will prompt for other volumes as they are needed. If the archive is on tape, you don't need to rewind the tape to to its beginning—if the tape head is positioned past the beginning of the archive, the script will rewind the tape as needed. See section Tape Positions and Tape Marks, for a discussion of tape positioning.
Warning: The script will delete files from the active file system if they were not in the file system when the archive was made.
See section Using tar to Perform Incremental Dumps, for an explanation of how the script makes
that determination.
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tar (This message will disappear, once this node revised.)
Certain options to tar enable you to specify a name for your
archive. Other options let you decide which files to include or exclude
from the archive, based on when or whether files were modified, whether
the file names do or don't match specified patterns, or whether files
are in specified directories.
This chapter discusses these options in detail.
| 6.1 Choosing and Naming Archive Files | Choosing the Archive's Name | |
| 6.2 Selecting Archive Members | ||
| 6.3 Reading Names from a File | ||
| 6.4 Excluding Some Files | ||
| 6.5 Wildcards Patterns and Matching | ||
| 6.6 Quoting Member Names | Ways of Quoting Special Characters in Names | |
| 6.7 Modifying File and Member Names | ||
| 6.8 Operating Only on New Files | ||
| 6.9 Descending into Directories | ||
| 6.10 Crossing File System Boundaries |
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(This message will disappear, once this node revised.)
By default, tar uses an archive file name that was compiled when
it was built on the system; usually this name refers to some physical
tape drive on the machine. However, the person who installed tar
on the system may not have set the default to a meaningful value as far as
most users are concerned. As a result, you will usually want to tell
tar where to find (or create) the archive. The
‘--file=archive-name’ (‘-f archive-name’)
option allows you to either specify or name a file to use as the archive
instead of the default archive file location.
Name the archive to create or operate on. Use in conjunction with any operation.
For example, in this tar command,
$ tar -cvf collection.tar blues folk jazz |
‘collection.tar’ is the name of the archive. It must directly
follow the ‘-f’ option, since whatever directly follows ‘-f’
will end up naming the archive. If you neglect to specify an
archive name, you may end up overwriting a file in the working directory
with the archive you create since tar will use this file's name
for the archive name.
An archive can be saved as a file in the file system, sent through a pipe or over a network, or written to an I/O device such as a tape, floppy disk, or CD write drive.
If you do not name the archive, tar uses the value of the
environment variable TAPE as the file name for the archive. If
that is not available, tar uses a default, compiled-in archive
name, usually that for tape unit zero (i.e., ‘/dev/tu00’).
If you use ‘-’ as an archive-name, tar reads the
archive from standard input (when listing or extracting files), or
writes it to standard output (when creating an archive). If you use
‘-’ as an archive-name when modifying an archive,
tar reads the original archive from its standard input and
writes the entire new archive to its standard output.
The following example is a convenient way of copying directory hierarchy from ‘sourcedir’ to ‘targetdir’.
$ (cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -) |
The ‘-C’ option allows to avoid using subshells:
$ tar -C sourcedir -cf - . | tar -C targetdir -xpf - |
In both examples above, the leftmost tar invocation archives
the contents of ‘sourcedir’ to the standard output, while the
rightmost one reads this archive from its standard input and
extracts it. The ‘-p’ option tells it to restore permissions
of the extracted files.
To specify an archive file on a device attached to a remote machine, use the following:
--file=hostname:/dev/file-name |
tar will complete the remote connection, if possible, and
prompt you for a username and password. If you use
‘--file=@hostname:/dev/file-name’, tar
will complete the remote connection, if possible, using your username
as the username on the remote machine.
If the archive file name includes a colon (‘:’), then it is assumed
to be a file on another machine. If the archive file is
‘user@host:file’, then file is used on the
host host. The remote host is accessed using the rsh
program, with a username of user. If the username is omitted
(along with the ‘@’ sign), then your user name will be used.
(This is the normal rsh behavior.) It is necessary for the
remote machine, in addition to permitting your rsh access, to
have the ‘rmt’ program installed (This command is included in
the GNU tar distribution and by default is installed under
‘prefix/libexec/rmt’, were prefix means your
installation prefix). If you need to use a file whose name includes a
colon, then the remote tape drive behavior
can be inhibited by using the ‘--force-local’ option.
When the archive is being created to ‘/dev/null’, GNU tar
tries to minimize input and output operations. The Amanda backup
system, when used with GNU tar, has an initial sizing pass which
uses this feature.
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File Name arguments specify which files in the file system
tar operates on, when creating or adding to an archive, or which
archive members tar operates on, when reading or deleting from
an archive. See section The Five Advanced tar Operations.
To specify file names, you can include them as the last arguments on the command line, as follows:
tar operation [option1 option2 …] [file name-1 file name-2 …] |
If a file name begins with dash (‘-’), precede it with ‘--add-file’ option to prevent it from being treated as an option.
By default GNU tar attempts to unquote each file or member
name, replacing escape sequences according to the following
table:
Escape | Replaced with |
|---|---|
\a | Audible bell (ASCII 7) |
\b | Backspace (ASCII 8) |
\f | Form feed (ASCII 12) |
\n | New line (ASCII 10) |
\r | Carriage return (ASCII 13) |
\t | Horizontal tabulation (ASCII 9) |
\v | Vertical tabulation (ASCII 11) |
\? | ASCII 127 |
\n | ASCII n (n should be an octal number of up to 3 digits) |
A backslash followed by any other symbol is retained.
This default behavior is controlled by the following command line option:
Enable unquoting input file or member names (default).
Disable unquoting input file or member names.
If you specify a directory name as a file name argument, all the files
in that directory are operated on by tar.
If you do not specify files, tar behavior differs depending
on the operation mode as described below:
When tar is invoked with ‘--create’ (‘-c’),
tar will stop immediately, reporting the following:
$ tar cf a.tar tar: Cowardly refusing to create an empty archive Try `tar --help' or `tar --usage' for more information. |
If you specify either ‘--list’ (‘-t’) or
‘--extract’ (‘--get’, ‘-x’), tar
operates on all the archive members in the archive.
If run with ‘--diff’ option, tar will compare the archive with the contents of the current working directory.
If you specify any other operation, tar does nothing.
By default, tar takes file names from the command line. However,
there are other ways to specify file or member names, or to modify the
manner in which tar selects the files or members upon which to
operate. In general, these methods work both for specifying the names
of files and archive members.
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Instead of giving the names of files or archive members on the command
line, you can put the names into a file, and then use the
‘--files-from=file-of-names’ (‘-T
file-of-names’) option to tar. Give the name of the
file which contains the list of files to include as the argument to
‘--files-from’. In the list, the file names should be separated by
newlines. You will frequently use this option when you have generated
the list of files to archive with the find utility.
Get names to extract or create from file file-name.
If you give a single dash as a file name for ‘--files-from’, (i.e.,
you specify either --files-from=- or -T -), then the file
names are read from standard input.
Unless you are running tar with ‘--create’, you can not use
both --files-from=- and --file=- (-f -) in the same
command.
Any number of ‘-T’ options can be given in the command line.
The following example shows how to use find to generate a list of
files smaller than 400K in length and put that list into a file
called ‘small-files’. You can then use the ‘-T’ option to
tar to specify the files from that file, ‘small-files’, to
create the archive ‘little.tgz’. (The ‘-z’ option to
tar compresses the archive with gzip; see section Creating and Reading Compressed Archives for
more information.)
$ find . -size -400 -print > small-files $ tar -c -v -z -T small-files -f little.tgz |
In the file list given by ‘-T’ option, any file name beginning
with ‘-’ character is considered a tar option and is
processed accordingly.(14) For example,
the common use of this feature is to change to another directory by
specifying ‘-C’ option:
$ cat list -C/etc passwd hosts -C/lib libc.a $ tar -c -f foo.tar --files-from list |
In this example, tar will first switch to ‘/etc’
directory and add files ‘passwd’ and ‘hosts’ to the
archive. Then it will change to ‘/lib’ directory and will archive
the file ‘libc.a’. Thus, the resulting archive ‘foo.tar’ will
contain:
$ tar tf foo.tar passwd hosts libc.a |
Notice that the option parsing algorithm used with ‘-T’ is stricter than the one used by shell. Namely, when specifying option arguments, you should observe the following rules:
-Cdir.
--directory=dir.
--directory dir |
and
-C dir |
If you happen to have a file whose name starts with ‘-’,
precede it with ‘--add-file’ option to prevent it from
being recognized as an option. For example: --add-file=--my-file.
6.3.1 NUL Terminated File Names |
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NUL Terminated File Names The ‘--null’ option causes
‘--files-from=file-of-names’ (‘-T file-of-names’)
to read file names terminated by a NUL instead of a newline, so
files whose names contain newlines can be archived using
‘--files-from’.
Only consider NUL terminated file names, instead of files that
terminate in a newline.
Undo the effect of any previous ‘--null’ option.
The ‘--null’ option is just like the one in GNU
xargs and cpio, and is useful with the
‘-print0’ predicate of GNU find. In
tar, ‘--null’ also disables special handling for
file names that begin with dash.
This example shows how to use find to generate a list of files
larger than 800K in length and put that list into a file called
‘long-files’. The ‘-print0’ option to find is just
like ‘-print’, except that it separates files with a NUL
rather than with a newline. You can then run tar with both the
‘--null’ and ‘-T’ options to specify that tar get the
files from that file, ‘long-files’, to create the archive
‘big.tgz’. The ‘--null’ option to tar will cause
tar to recognize the NUL separator between files.
$ find . -size +800 -print0 > long-files $ tar -c -v --null --files-from=long-files --file=big.tar |
The ‘--no-null’ option can be used if you need to read both zero-terminated and newline-terminated files on the same command line. For example, if ‘flist’ is a newline-terminated file, then the following command can be used to combine it with the above command:
$ find . -size +800 -print0 | tar -c -f big.tar --null -T - --no-null -T flist |
This example uses short options for typographic reasons, to avoid very long lines.
GNU tar is able to automatically detect null-terminated file lists, so
it is safe to use them even without the ‘--null’ option. In
this case tar will print a warning and continue reading such
a file as if ‘--null’ were actually given:
$ find . -size +800 -print0 | tar -c -f big.tar -T - tar: -: file name read contains nul character |
The null terminator, however, remains in effect only for this particular file, any following ‘-T’ options will assume newline termination. Of course, the null autodetection applies to these eventual surplus ‘-T’ options as well.
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(This message will disappear, once this node revised.)
To avoid operating on files whose names match a particular pattern, use the ‘--exclude’ or ‘--exclude-from’ options.
Causes tar to ignore files that match the pattern.
The ‘--exclude=pattern’ option prevents any file or member whose name matches the shell wildcard (pattern) from being operated on. For example, to create an archive with all the contents of the directory ‘src’ except for files whose names end in ‘.o’, use the command ‘tar -cf src.tar --exclude='*.o' src’.
You may give multiple ‘--exclude’ options.
Causes tar to ignore files that match the patterns listed in
file.
Use the ‘--exclude-from’ option to read a
list of patterns, one per line, from file; tar will
ignore files matching those patterns. Thus if tar is
called as ‘tar -c -X foo .’ and the file ‘foo’ contains a
single line ‘*.o’, no files whose names end in ‘.o’ will be
added to the archive.
Notice, that lines from file are read verbatim. One of the frequent errors is leaving some extra whitespace after a file name, which is difficult to catch using text editors.
However, empty lines are OK.
Exclude files and directories used by following version control systems: ‘CVS’, ‘RCS’, ‘SCCS’, ‘SVN’, ‘Arch’, ‘Bazaar’, ‘Mercurial’, and ‘Darcs’.
As of version 1.22, the following files are excluded:
When creating an archive, the ‘--exclude-caches’ option family
causes tar to exclude all directories that contain a cache
directory tag. A cache directory tag is a short file with the
well-known name ‘CACHEDIR.TAG’ and having a standard header
specified in http://www.brynosaurus.com/cachedir/spec.html.
Various applications write cache directory tags into directories they
use to hold regenerable, non-precious data, so that such data can be
more easily excluded from backups.
There are three ‘exclude-caches’ options, each providing a different exclusion semantics:
Do not archive the contents of the directory, but archive the directory itself and the ‘CACHEDIR.TAG’ file.
Do not archive the contents of the directory, nor the ‘CACHEDIR.TAG’ file, archive only the directory itself.
Omit directories containing ‘CACHEDIR.TAG’ file entirely.
Another option family, ‘--exclude-tag’, provides a generalization of this concept. It takes a single argument, a file name to look for. Any directory that contains this file will be excluded from the dump. Similarly to ‘exclude-caches’, there are three options in this option family:
Do not dump the contents of the directory, but dump the directory itself and the file.
Do not dump the contents of the directory, nor the file, archive only the directory itself.
Omit directories containing file file entirely.
Multiple ‘--exclude-tag*’ options can be given.
For example, given this directory:
$ find dir dir dir/blues dir/jazz dir/folk dir/folk/tagfile dir/folk/sanjuan dir/folk/trote |
The ‘--exclude-tag’ will produce the following:
$ tar -cf archive.tar --exclude-tag=tagfile -v dir dir/ dir/blues dir/jazz dir/folk/ tar: dir/folk/: contains a cache directory tag tagfile; contents not dumped dir/folk/tagfile |
Both the ‘dir/folk’ directory and its tagfile are preserved in the archive, however the rest of files in this directory are not.
Now, using the ‘--exclude-tag-under’ option will exclude ‘tagfile’ from the dump, while still preserving the directory itself, as shown in this example:
$ tar -cf archive.tar --exclude-tag-under=tagfile -v dir dir/ dir/blues dir/jazz dir/folk/ ./tar: dir/folk/: contains a cache directory tag tagfile; contents not dumped |
Finally, using ‘--exclude-tag-all’ omits the ‘dir/folk’ directory entirely:
$ tar -cf archive.tar --exclude-tag-all=tagfile -v dir dir/ dir/blues dir/jazz ./tar: dir/folk/: contains a cache directory tag tagfile; directory not dumped |
Problems with Using the exclude Options |
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exclude Options Some users find ‘exclude’ options confusing. Here are some common pitfalls:
tar does not act on a file name
explicitly listed on the command line, if one of its file name
components is excluded. In the example above, if
you create an archive and exclude files that end with ‘*.o’, but
explicitly name the file ‘dir.o/foo’ after all the options have been
listed, ‘dir.o/foo’ will be excluded from the archive.
tar sees wildcard characters
like ‘*’. If you do not do this, the shell might expand the
‘*’ itself using files at hand, so tar might receive a
list of files instead of one pattern, or none at all, making the
command somewhat illegal. This might not correspond to what you want.
For example, write:
$ tar -c -f archive.tar --exclude '*.o' directory |
rather than:
# Wrong! $ tar -c -f archive.tar --exclude *.o directory |
regexp
syntax, when using exclude options in tar. If you try to use
regexp syntax to describe files to be excluded, your command
might fail.
tar, what is now the
‘--exclude-from’ option was called ‘--exclude’ instead.
Now, ‘--exclude’ applies to patterns listed on the command
line and ‘--exclude-from’ applies to patterns listed in a
file.
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Globbing is the operation by which wildcard characters,
‘*’ or ‘?’ for example, are replaced and expanded into all
existing files matching the given pattern. GNU tar can use wildcard
patterns for matching (or globbing) archive members when extracting
from or listing an archive. Wildcard patterns are also used for
verifying volume labels of tar archives. This section has the
purpose of explaining wildcard syntax for tar.
A pattern should be written according to shell syntax, using wildcard characters to effect globbing. Most characters in the pattern stand for themselves in the matched string, and case is significant: ‘a’ will match only ‘a’, and not ‘A’. The character ‘?’ in the pattern matches any single character in the matched string. The character ‘*’ in the pattern matches zero, one, or more single characters in the matched string. The character ‘\’ says to take the following character of the pattern literally; it is useful when one needs to match the ‘?’, ‘*’, ‘[’ or ‘\’ characters, themselves.
The character ‘[’, up to the matching ‘]’, introduces a character class. A character class is a list of acceptable characters for the next single character of the matched string. For example, ‘[abcde]’ would match any of the first five letters of the alphabet. Note that within a character class, all of the “special characters” listed above other than ‘\’ lose their special meaning; for example, ‘[-\\[*?]]’ would match any of the characters, ‘-’, ‘\’, ‘[’, ‘*’, ‘?’, or ‘]’. (Due to parsing constraints, the characters ‘-’ and ‘]’ must either come first or last in a character class.)
If the first character of the class after the opening ‘[’ is ‘!’ or ‘^’, then the meaning of the class is reversed. Rather than listing character to match, it lists those characters which are forbidden as the next single character of the matched string.
Other characters of the class stand for themselves. The special construction ‘[a-e]’, using an hyphen between two letters, is meant to represent all characters between a and e, inclusive.
Periods (‘.’) or forward slashes (‘/’) are not considered special for wildcard matches. However, if a pattern completely matches a directory prefix of a matched string, then it matches the full matched string: thus, excluding a directory also excludes all the files beneath it.
| Controlling Pattern-Matching |
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For the purposes of this section, we call exclusion members all member names obtained while processing ‘--exclude’ and ‘--exclude-from’ options, and inclusion members those member names that were given in the command line or read from the file specified with ‘--files-from’ option.
These two pairs of member lists are used in the following operations: ‘--diff’, ‘--extract’, ‘--list’, ‘--update’.
There are no inclusion members in create mode (‘--create’ and ‘--append’), since in this mode the names obtained from the command line refer to files, not archive members.
By default, inclusion members are compared with archive members literally (15) and exclusion members are treated as globbing patterns. For example:
$ tar tf foo.tar a.c b.c a.txt [remarks] # Member names are used verbatim: $ tar -xf foo.tar -v '[remarks]' [remarks] # Exclude member names are globbed: $ tar -xf foo.tar -v --exclude '*.c' a.txt [remarks] |
This behavior can be altered by using the following options:
Treat all member names as wildcards.
Treat all member names as literal strings.
Thus, to extract files whose names end in ‘.c’, you can use:
$ tar -xf foo.tar -v --wildcards '*.c' a.c b.c |
Notice quoting of the pattern to prevent the shell from interpreting it.
The effect of ‘--wildcards’ option is canceled by ‘--no-wildcards’. This can be used to pass part of the command line arguments verbatim and other part as globbing patterns. For example, the following invocation:
$ tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]' |
instructs tar to extract from ‘foo.tar’ all files whose
names end in ‘.txt’ and the file named ‘[remarks]’.
Normally, a pattern matches a name if an initial subsequence of the name's components matches the pattern, where ‘*’, ‘?’, and ‘[...]’ are the usual shell wildcards, ‘\’ escapes wildcards, and wildcards can match ‘/’.
Other than optionally stripping leading ‘/’ from names (see section Absolute File Names), patterns and names are used as-is. For example, trailing ‘/’ is not trimmed from a user-specified name before deciding whether to exclude it.
However, this matching procedure can be altered by the options listed below. These options accumulate. For example:
--ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme' |
ignores case when excluding ‘makefile’, but not when excluding ‘readme’.
If anchored, a pattern must match an initial subsequence of the name's components. Otherwise, the pattern can match any subsequence. Default is ‘--no-anchored’ for exclusion members and ‘--anchored’ inclusion members.
When ignoring case, upper-case patterns match lower-case names and vice versa. When not ignoring case (the default), matching is case-sensitive.
When wildcards match slash (the default for exclusion members), a wildcard like ‘*’ in the pattern can match a ‘/’ in the name. Otherwise, ‘/’ is matched only by ‘/’.
The ‘--recursion’ and ‘--no-recursion’ options (see section Descending into Directories) also affect how member patterns are interpreted. If recursion is in effect, a pattern matches a name if it matches any of the name's parent directories.
The following table summarizes pattern-matching default values:
Members | Default settings |
|---|---|
Inclusion | ‘--no-wildcards --anchored --no-wildcards-match-slash’ |
Exclusion | ‘--wildcards --no-anchored --wildcards-match-slash’ |
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When displaying member names, tar takes care to avoid
ambiguities caused by certain characters. This is called name
quoting. The characters in question are:
Character | ASCII | Character name |
|---|---|---|
\a | 7 | Audible bell |
\b | 8 | Backspace |
\f | 12 | Form feed |
\n | 10 | New line |
\r | 13 | Carriage return |
\t | 9 | Horizontal tabulation |
\v | 11 | Vertical tabulation |
The exact way tar uses to quote these characters depends on
the quoting style. The default quoting style, called
escape (see below), uses backslash notation to represent control
characters, space and backslash. Using this quoting style, control
characters are represented as listed in column ‘Character’ in the
above table, a space is printed as ‘\ ’ and a backslash as ‘\\’.
GNU tar offers seven distinct quoting styles, which can be selected
using ‘--quoting-style’ option:
Sets quoting style. Valid values for style argument are: literal, shell, shell-always, c, escape, locale, clocale.
These styles are described in detail below. To illustrate their effect, we will use an imaginary tar archive ‘arch.tar’ containing the following members:
# 1. Contains horizontal tabulation character. a tab # 2. Contains newline character a newline # 3. Contains a space a space # 4. Contains double quotes a"double"quote # 5. Contains single quotes a'single'quote # 6. Contains a backslash character: a\backslash |
Here is how usual ls command would have listed them, if they
had existed in the current working directory:
$ ls a\ttab a\nnewline a\ space a"double"quote a'single'quote a\\backslash |
Quoting styles:
No quoting, display each character as is:
$ tar tf arch.tar --quoting-style=literal ./ ./a space ./a'single'quote ./a"double"quote ./a\backslash ./a tab ./a newline |
Display characters the same way Bourne shell does: control characters, except ‘\t’ and ‘\n’, are printed using backslash escapes, ‘\t’ and ‘\n’ are printed as is, and a single quote is printed as ‘\'’. If a name contains any quoted characters, it is enclosed in single quotes. In particular, if a name contains single quotes, it is printed as several single-quoted strings:
$ tar tf arch.tar --quoting-style=shell ./ './a space' './a'\''single'\''quote' './a"double"quote' './a\backslash' './a tab' './a newline' |
Same as ‘shell’, but the names are always enclosed in single quotes:
$ tar tf arch.tar --quoting-style=shell-always './' './a space' './a'\''single'\''quote' './a"double"quote' './a\backslash' './a tab' './a newline' |
Use the notation of the C programming language. All names are enclosed in double quotes. Control characters are quoted using backslash notations, double quotes are represented as ‘\"’, backslash characters are represented as ‘\\’. Single quotes and spaces are not quoted:
$ tar tf arch.tar --quoting-style=c "./" "./a space" "./a'single'quote" "./a\"double\"quote" "./a\\backslash" "./a\ttab" "./a\nnewline" |
Control characters are printed using backslash notation, a space is printed as ‘\ ’ and a backslash as ‘\\’. This is the default quoting style, unless it was changed when configured the package.
$ tar tf arch.tar --quoting-style=escape ./ ./a space ./a'single'quote ./a"double"quote ./a\\backslash ./a\ttab ./a\nnewline |
Control characters, single quote and backslash are printed using backslash notation. All names are quoted using left and right quotation marks, appropriate to the current locale. If it does not define quotation marks, use ‘`’ as left and ‘'’ as right quotation marks. Any occurrences of the right quotation mark in a name are escaped with ‘\’, for example:
For example:
$ tar tf arch.tar --quoting-style=locale `./' `./a space' `./a\'single\'quote' `./a"double"quote' `./a\\backslash' `./a\ttab' `./a\nnewline' |
Same as ‘locale’, but ‘"’ is used for both left and right quotation marks, if not provided by the currently selected locale:
$ tar tf arch.tar --quoting-style=clocale "./" "./a space" "./a'single'quote" "./a\"double\"quote" "./a\\backslash" "./a\ttab" "./a\nnewline" |
You can specify which characters should be quoted in addition to those implied by the current quoting style:
Always quote characters from string, even if the selected quoting style would not quote them.
For example, using ‘escape’ quoting (compare with the usual escape listing above):
$ tar tf arch.tar --quoting-style=escape --quote-chars=' "' ./ ./a\ space ./a'single'quote ./a\"double\"quote ./a\\backslash ./a\ttab ./a\nnewline |
To disable quoting of such additional characters, use the following option:
Remove characters listed in string from the list of quoted characters set by the previous ‘--quote-chars’ option.
This option is particularly useful if you have added
‘--quote-chars’ to your TAR_OPTIONS (see TAR_OPTIONS)
and wish to disable it for the current invocation.
Note, that ‘--no-quote-chars’ does not disable those characters that are quoted by default in the selected quoting style.
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Tar archives contain detailed information about files stored
in them and full file names are part of that information. When
storing file to an archive, its file name is recorded in it,
along with the actual file contents. When restoring from an archive,
a file is created on disk with exactly the same name as that stored
in the archive. In the majority of cases this is the desired behavior
of a file archiver. However, there are some cases when it is not.
First of all, it is often unsafe to extract archive members with
absolute file names or those that begin with a ‘../’. GNU tar
takes special precautions when extracting such names and provides a
special option for handling them, which is described in
Absolute File Names.
Secondly, you may wish to extract file names without some leading directory components, or with otherwise modified names. In other cases it is desirable to store files under differing names in the archive.
GNU tar provides several options for these needs.
Strip given number of leading components from file names before extraction.
For example, suppose you have archived whole ‘/usr’ hierarchy to a tar archive named ‘usr.tar’. Among other files, this archive contains ‘usr/include/stdlib.h’, which you wish to extract to the current working directory. To do so, you type:
$ tar -xf usr.tar --strip=2 usr/include/stdlib.h |
The option ‘--strip=2’ instructs tar to strip the
two leading components (‘usr/’ and ‘include/’) off the file
name.
If you add the ‘--verbose’ (‘-v’) option to the invocation
above, you will note that the verbose listing still contains the
full file name, with the two removed components still in place. This
can be inconvenient, so tar provides a special option for
altering this behavior:
Display file or member names with all requested transformations applied.
For example:
$ tar -xf usr.tar -v --strip=2 usr/include/stdlib.h usr/include/stdlib.h $ tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h stdlib.h |
Notice that in both cases the file ‘stdlib.h’ is extracted to the current working directory, ‘--show-transformed-names’ affects only the way its name is displayed.
This option is especially useful for verifying whether the invocation will have the desired effect. Thus, before running
$ tar -x --strip=n |
it is often advisable to run
$ tar -t -v --show-transformed --strip=n |
to make sure the command will produce the intended results.
In case you need to apply more complex modifications to the file name,
GNU tar provides a general-purpose transformation option:
Modify file names using supplied expression.
The expression is a sed-like repl