tar
tar
tar
Operations
tar
Operations
tar
Operations
--extract
tar
Usages
tar
Welcome to the GNU tar manual. GNU tar is
used to create and manipulate files (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 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.
@FIXME{this sounds more like a GNU Project Manuals Concept [tm] more than the reality. should think about whether this makes sense to say here, or not.} 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 The Standard Format) contains a big quote
which is taken directly from tar sources.
In general, we give both the 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.)
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
last 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 filesystem, 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
filesystem. 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 peformed using tar.
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).
@FIXME{the following table entries need a bit of work..}
You can use tar archives in many ways. We want to stress a
few of them: storage, backup, and transportation.
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!)
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 filesystem.
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.
@FIXME{must ask franc,ois about this. dan hagerty thinks this might be an issue, but we're not really sure at this time. dan just tried a test case of mixing up options' orders while the variable was set, and there was no problem...}
We make some of our recommendations throughout this book for one reason
in addition to what we think of as "good sense". The main
additional reason for a recommendation is to be compliant with the
POSIX standards. If you set the shell environment variable POSIXLY_CORRECT,
GNU tar will force you to adhere to these standards.
Therefore, if this variable is set and you violate one of the POSIX
standards in the way you phrase a command, for example, GNU tar
will not allow the command and will signal an error message. You would
then have to reorder the options or rephrase the command to comply with
the POSIX standards.
There is a chance in the future that, if you set this environment
variable, your archives will be forced to comply with POSIX standards,
also. No GNU tar extensions will be allowed.
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, and finally Fran@,{c}ois Pinard,
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.
@FIXME{i want all of these names mentioned, Absolutely. BUT, i'm not sure i want to spell out the history in this detail, at least not for the printed book. i'm just not sure it needs to be said this way. i'll think about it.}
@FIXME{History is more important, and surely more interesting, than actual names. Quoting names without history would be meaningless. FP}
Jay Fenlason put together a draft of a GNU tar manual,
borrowing notes from the original man page from John Gilmore. This
draft has been distributed in tar versions 1.04 (or even
before?) @FIXME{huh? IMO, either we know or we don't; the parenthetical
is confusing.} through 1.10, then withdrawn in version 1.11. Thomas
Bushnell, n/BSG and Amy Gorin worked on a tutorial and manual for GNU tar.
Fran@,{c}ois 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.
@FIXME{update version number as necessary; i'm being optimistic!}
@FIXME{Someone [maybe karl berry? maybe bob chassell? maybe melissa?
maybe julie sussman?] needs to properly index the thing.}
For version 1.12, Daniel Hagerty contributed a great deal of technical consulting. In particular, he is the primary author of section Performing Backups and Restoring Files.
If you find problems or have suggestions about this program or manual, please report them to `bug-gnu-utils@prep.ai.mit.edu'.
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.
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
path names, we will assume that those paths are relative to your home
directory. For example, my home directory path is `/home/fsf/melissa'.
All of my examples are in a subdirectory of the directory named by that
path name; the subdirectory is called `practice'.
tar
archives with tape drives. @FIXME{this is a cop out. need to add some
simple tape drive info.}
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'. When we have lines which are too
long to be displayed in any other way, we will show them like this:
This is an example of a line which would otherwise not fit in this space.
@FIXME{how often do we use smallexample?}
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. @FIXME{make sure this is
still the case, at the end} 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. We present a full discussion
of this way of writing options and operations appears in section Old Option Style, and we discuss the other
two styles of writing options in section Mnemonic
Option Style and 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 section 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.
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.
tar archive.
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.)
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 use a
default, usually some physical tape drive attached to your machine. 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 specfiy 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 section Choosing and Naming
Archive Files.
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.
Sometimes, a single instance of `--verbose' on the command line will show a full, `ls' style listing of an archive or files, giving sizes, owners, and similar information. Other times, `--verbose' will only show files or members that the particular operation is operating on at the time. In the latter case, you can use `--verbose' twice in a command to get a listing such as that in the former case. For example, instead of saying
tar -cvf afiles.tar apple angst aspic
above, you might say
tar -cvvf afiles.tar apple angst 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'.
--help
Optiontar prints out a
very brief list of all operations and option available for the current
version of tar available on your system.
@UNREVISED
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.
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 path 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 a file unless you
specify an option which does this @FIXME{xref to the node for
--backup!}. To add files to an existing archive, you need to use a
different option, such as --append (-r); see
section How to Add Files to Existing Archives: --append
for information on how to do this.
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 part of the command which says, --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) @FIXME{xref here to the discussion of file name args?}. Now that they are are in the archive, they are called archive members, not files @FIXME{xref to definitions?}.
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.
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 (note the
different font styles).
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.
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 section 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.
@FIXME{i don't like how this is worded:} 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.
(Placing options in an unusual order can also cause tar to
report an error if you have set the shell environment variable, POSIXLY_CORRECT;
see section POSIX Compliance for more
information on this.)
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, 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
versions of tar are not 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.
@FIXME{bob doesn't like this sentence, since he does it all the time,
and we've been doing it in the editing passes for this manual: In
general, make sure that the archive is not inside a directory being
dumped.})
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
@FIXME{we hope this will change. if it doesn't, need to show the creation of bfiles somewhere above!!! : }
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.
If you had used --verbose (-v) mode, the example above would look like:
$ tar --list --verbose --file=collection.tar folk -rw-rw-rw- myself user 62 1990-05-23 10:55 folk
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'.
@FIXME{we hope the relevant aspects of this will change:}Because tar
preserves paths, file names must be specified as they appear in the
archive (ie., 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 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 are compared using a
simplistic name comparison, in which an exact match is necessary. See
section Absolute File Names.
However, tar --list --file=collection.tar folk would respond
with `folk', because `folk' is in the archive file `collection.tar'.
If you are not sure of the exact file name, try listing all the files
in the archive and searching for the one you expect to find; remember
that if you use `--list' with no file names as arguments, tar
will print the names of all the members stored in the specified
archive.
@UNREVISED
@FIXME{i changed the order of these nodes around and haven't had a chance to play around with this node's example, yet. i have to play with it and see what it actually does for my own satisfaction, even if what it says *is* correct..}
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-rw-rw- myself user 42 1990-05-21 13:29 practice/blues -rw-rw-rw- myself user 62 1990-05-23 10:55 practice/folk -rw-rw-rw- myself user 40 1990-05-21 13:30 practice/jazz -rw-rw-rw- 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.
@UNREVISED
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, -x) operation. As with --create (-c), specify the name of the archive with --file=archive-name (-f archive-name). 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.
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-rw-rw- me user 28 1996-10-18 16:31 jazz -rw-rw-rw- me user 21 1996-09-23 16:44 blues -rw-rw-rw- me user 20 1996-09-23 16:44 folk
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. It will be identical to the original file `blues' that you deleted. @FIXME{check this; will the times, permissions, owner, etc be the same, also?}
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,
creation times, and owner. @FIXME{This is only accidentally true, but
not in general. In most cases, one has to be root for restoring the
owner, and use a special option for restoring permissions. Here, it
just happens that the restoring user is also the owner of the archived
members, and that the current umask is compatible with
original permissions.} (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).
@FIXME{we hope this will change:}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. To find the exact member names of the members of an archive, use --list (-t) (see section How to List Archives).
If you give the --verbose (-v) option, then --extract (--get, -x) will print the names of the archive members as it extracts them.
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 overwrite 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.
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
@FIXME{need to show tar's response; used verbose above. also, here's a good place to demonstrate the -v -v thing. have to write that up (should be trivial, but i'm too tired!).}
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.
@FIXME{IMPORTANT! show the final structure, here. figure out what it will be.}
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
@FIXME{make sure the above works when going through the examples in order...}
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 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.
@FIXME{more examples, here? hag thinks it's a good idea.}
@FIXME{need to write up a node here about the things that are going to be in the rest of the manual.}
tar@UNREVISED
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 (-v) (see section Checking tar progress) and --interactive
(-w) options (see section Asking
for Confirmation During Operations).
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 (-t). 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
(-P) option). See section Absolute
File Names, for more information about --absolute-names (-P).
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 filesystem 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 (-t), --extract
(--get, -x), --compare (--diff, -d),
and --update (-u)) 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 is improperly written. Errors may be
encountered later, while encountering an error 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 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.
GNU tar returns only a few exit statuses. I'm really
aiming simplicity in that area, for now. If you are not using the --compare
(--diff, -d) option, zero means that everything
went well, besides maybe innocuous warnings. Nonzero means that
something went wrong. Right now, as of today, "nonzero" is
almost always 2, except for remote operations, where it may be 128.
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 (two lists of four operations each may be found at section The Three Most Frequently Used Operations
and section 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.)
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.
@FIXME{menu at end of this node. need to think of an actual outline for this chapter; probably do that after stuff from chap. 4 is incorporated.}
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=archive-name
(-f archive-name) 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.
@FIXME{hag to write a brief paragraph on the option(s) which can optionally take an argument}
@FIXME{have to decide whether or ot to replace other occurrences of "mnemonic" with "long", or *ugh* vice versa.}
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 mnemonic option has many different 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 mnemonic 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.)
Mnemonic 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.
Mnemonic options which require arguments take those arguments
immediately following the option name; they are introduced by an equal
sign. 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 the notation `--file=archive.tar'
for the mnemonic option.
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' 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(1).
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.
@UNREVISED
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(2). This set of letters must be the first to appear
on the command line, after the tar program name and some
whitespace; 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
mnemonic option `--list'. So for example, the command `tar
cv' specifies the option `-v' in addition to the
operation `-c'.
@FIXME{bob suggests having an uglier example. :-) }
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
@FIXME{still could explain this better; it's redundant:}
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.
All three styles may be intermixed in a single tar
command, so long as the rules for each style are fully respected(3). 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
whitespace). 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. @FIXME{not sure i liked the first sentence of
this paragraph..}
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.
--append.
--concatenate.
tar archives to the end of the archive.
See section Combining Archives with --concatenate.
tar archive. See section How to Create Archives.
tar Optionstar strips an
initial `/' from member names. This option disables
that behavior. @FIXME-xref{}.
tar to preserve the access time field in a
file's inode when dumping it. @FIXME-xref{}.
tar
will back them up using simple or numbered backups, depending upon backup-type.
@FIXME-xref{}.
tar prints error messages
for read errors with the block number in the archive file.
@FIXME-xref{}.
tar uses to blocking
x 512 bytes per record. @FIXME-xref{}.
tar to print periodic checkpoint
messages as it reads through the archive. Its intended for when you
want a visual indication that tar is still running,
but don't want to see `--verbose' output.
@FIXME-xref{}.
tar will use the compress program when
reading or writing the archive. This allows you to directly act on
archives while saving space. @FIXME-xref{}.
tar archive, tar will
archive the file that a symbolic link points to, rather than archiving
the symlink. @FIXME-xref{}.
tar will change its
current directory to dir before performing any
operations. When this option is used during archive creation, it is
order sensitive. @FIXME-xref{}.
tar will skip files that
match pattern. @FIXME-xref{}.
tar will
use the list of patterns in the file file.
@FIXME-xref{}.
tar will use the file archive as the tar
archive it performs operations on, rather than tar's
compilation dependent default. @FIXME-xref{}.
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. @FIXME-xref{}.
tar to interpret the filename given to `--file'
as a local file, even if it looks like a remote tape drive name.
@FIXME-xref{}.
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. @FIXME-xref{}. Also see
the comments for the --owner=user option.
tar to read or write archives
through gzip, allowing tar to directly
operate on several kinds of compressed archives transparently.
@FIXME-xref{}.
tar will print out a short message summarizing the
operations and options to tar and exit. @FIXME-xref{}.
tar to exit successfully if it encounters an
unreadable file. See section Options to
Help Read Archives.
tar
Writes Files.)
tar will ignore zeroed blocks in the
archive, which normally signals EOF. See section Options to Help Read Archives.
tar that it is working with an old
GNU-format incremental backup archive. It is intended primarily for
backwards compatibility only. @FIXME-xref{}.
tar is performing multi-tape backups, script-file
is run at the end of each tape. @FIXME-xref{}.
tar should ask the user for
confirmation before performing potentially destructive options, such as
overwriting files. @FIXME-xref{}.
tar will not
overwrite existing files if this option is present. See section Changing How tar Writes Files.
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. @FIXME-xref{}.
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. @FIXME-xref{}.
tar will use permissions
for the archive members, rather than the permissions from the files.
The program chmod and this tar option
share the same syntax for what permissions might be. See
section `File permissions' in GNU file utilities. This
reference also has useful information for those not being overly
familiar with the Unix permission system. Of course, permissions
might be plainly specified as an octal number. However, by using
generic symbolic modifications to mode bits, this allows 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 that it should create or otherwise operate
on a multi-volume tar archive. @FIXME-xref{}.
tar will only add files that
have changed since date. @FIXME-xref{}.
tar will
only add files whose contents have changed (as opposed to just `--newer',
which will also back up files for which any status information has
changed).
tar will not recurse into
directories unless a directory is explicitly named as an argument to tar.
@FIXME-xref{}.
tar is using the `--files-from'
option, this option instructs tar to expect filenames
terminated with NUL, so tar can correctly
work with file names that contain newlines. @FIXME-xref{}.
tar that it should use numeric
user and group IDs when creating a tar file, rather
than names. @FIXME-xref{}.
tar from
recursing into directories that are on different file systems from the
current directory. @FIXME-xref{}.
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. @FIXME-xref{}. 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.
tar to create an archive that is compatible with
Unix V7 tar. @FIXME-xref{}.
tar to create a POSIX compliant tar
archive. @FIXME-xref{}.
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 Changing How tar
Writes Files.
tar should reblock its input, for
reading from pipes on systems with buggy implementations. See section Options to Help Read Archives.
tar to use size bytes per record
when accessing the archive. @FIXME-xref{}.
tar Writes Files.
tar to remove the source file from the file
system after appending it to an archive. @FIXME-xref{}.
tar that is should use cmd to
communicate with remote devices. @FIXME-xref{}.
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.
tar will attempt to
preserve the owner specified in the tar archive with
this option present. @FIXME-xref{}.
tar Writes Files.)
tar to mention directories its skipping over
when operating on a tar archive. @FIXME-xref{}.
tar will skip
extracting files in the archive until it finds one that matches name.
See section Coping with Scarce Resources.
tar uses when backing up files from
the default `~'. @FIXME-xref{}.
tar is writing as
being num x 1024 bytes long. @FIXME-xref{}.
tar will extract files to stdout
rather than to the file system. See section Changing How tar Writes Files.
tar Writes Files.
tar to remove the corresponding file from the
file system before extracting it from the archive. See section Changing How tar Writes Files.
tar to access the archive through prog,
which is presumed to be a compression program of some sort.
@FIXME-xref{}.
tar should be more verbose about the
operations its performing. This option can be specified multiple times
for some operations to increase the amount of information displayed.
@FIXME-xref{}.
tar will print an informational message about what
version it is and a copyright message, some credits, and then exit.
@FIXME-xref{}.
tar
will keep track of which volume of a multi-volume archive its working
in file. @FIXME-xref{}.
Here is an alphabetized list of all of the short option forms, matching them with the equivalent long option.
tar documentation
Being careful, the first thing is really checking that you are using
GNU tar, indeed. The --version option will
generate a message giving confirmation that you are using GNU tar,
with the precise version of GNU tar you are using. tar
identifies itself and prints the version number to the standard
output, then immediately exits successfully, without doing anything
else, ignoring all other options. For example, `tar --version'
might return:
tar (GNU tar) 1.12
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(4).
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.
The perceptive reader would have noticed some contradiction in the previous paragraphs. It is written that both --version and --help print something, and have all other options ignored. In fact, they cannot ignore each other, and one of them has to win. We do not specify which is stronger, here; experiment if you really wonder!
The short help output is quite succint, 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 printed form, as a kind of small book. It
may 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 long to GNU tar, or it has not
been produced by GNU. Currently, GNU tar documentation is
provided in Texinfo format only, if we except, of course, the short
result of tar --help.
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 (-c) or --extract (--get, -x), --verbose
(-v) 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 (reminiscent of `ls -l') for
each member. Since --list (-t) already prints the
names of the members, --verbose (-v) used once
with --list (-t) 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 xvv 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.
The --totals option--which is only meaningful when used with --create
(-c)---causes tar to print the total amount
written to the archive, after it has been fully created.
The --checkpoint option prints an occasional message as tar
reads or writes the archive. In fact, it print directory names while
reading 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.
@FIXME{There is some confusion here. It seems that -R once wrote a message at `every' record read or written.}
The --show-omitted-dirs option, when reading an archive--with --list (-t) or --extract (--get, -x), 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
if 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). @FIXME-xref{when the node name is set and the backup section written}.
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.
tar Operationstar
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.
tar
to destroy a magnetic tape with an empty archive(5). 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 ot 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 catastrophical nature of these
errors, GNU tar now takes some distance from elegance,
and cowardly refuses to create an archive when --create (-c)
option is given, there are no arguments besides options, and --files-from=file-of-names
(-T file-of-names) 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=file-of-names
(-T file-of-names) 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
tar archive, as a
pipe.
tar now shows dates as `1996-11-09',
while it used to show them as `Nov 11 1996'. (One can
revert to the old behavior by defining USE_OLD_CTIME
in `src/list.c' before reinstalling.) But preferrably,
people you should get used to ISO 8601 dates. Local American dates
should be made available again with full date localisation support,
once ready. In the meantime, programs not being localisable for dates
should prefer international dates, that's really the way to go. Look up http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html
if you are curious, it contains a detailed explanation of the ISO 8601
standard.
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 defin