tar.texi

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@file{collection.tar}.

This section will proceed slowly, detailing how to use @option{--create}
in @code{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
@command{tar} works.

@menu
* prepare for examples::
* Creating the archive::
* create verbose::
* short create::
* create dir::
@end menu

@node prepare for examples
@subsection Preparing a Practice Directory for Examples

To follow along with this and future examples, create a new directory
called @file{practice} containing files called @file{blues}, @file{folk}
and @file{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 @file{practice}
is a subdirectory of your home directory.

Now @command{cd} to the directory named @file{practice}; @file{practice}
is now your @dfn{working directory}.  (@emph{Please note}: Although
the full file name of this directory is
@file{/@var{homedir}/practice}, in our examples we will refer to
this directory as @file{practice}; the @var{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 @command{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,
@samp{collection.tar}), or that you don't care about its contents.
Whenever you use @samp{create}, @command{tar} will erase the current
contents of the file named by @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) if it exists.  @command{tar}
will not tell you if you are about to overwrite an archive unless you
specify an option which does this (@pxref{backup}, for the
information on how to do so).  To add files to an existing archive,
you need to use a different option, such as @option{--append} (@option{-r}); see
@ref{append} for information on how to do this.

@node Creating the archive
@subsection Creating the Archive

@xopindex{create, introduced}
To place the files @file{blues}, @file{folk}, and @file{jazz} into an
archive named @file{collection.tar}, use the following command:

@smallexample
$ @kbd{tar --create --file=collection.tar blues folk jazz}
@end smallexample

The order of the arguments is not very important, @emph{when using long
option forms}.  You could also say:

@smallexample
$ @kbd{tar blues --create folk --file=collection.tar jazz}
@end smallexample

@noindent
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
@command{tar}, to avoid errors).

Note that the sequence
@option{--file=@-collection.tar} is considered to be @emph{one} argument.
If you substituted any other string of characters for
@kbd{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.
@xref{short create}, for more information on this.

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

When you create an archive, you @emph{must} specify which files you
want placed in the archive.  If you do not specify any archive
members, @GNUTAR{} will complain.

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

@smallexample
blues   folk   jazz   collection.tar
@end smallexample

@noindent
Creating the archive @samp{collection.tar} did not destroy the copies of
the files in the directory.

Keep in mind that if you don't indicate an operation, @command{tar} will not
run and will prompt you for one.  If you don't name any files, @command{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.

@emph{Caution}: Do not attempt to use @option{--create} (@option{-c}) to add files to
an existing archive; it will delete the archive and write a new one.
Use @option{--append} (@option{-r}) instead.  @xref{append}.

@node create verbose
@subsection Running @option{--create} with @option{--verbose}

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

@smallexample
$ @kbd{tar --create --verbose --file=collection.tar blues folk jazz}
blues
folk
jazz
@end smallexample

This example is just like the example we showed which did not use
@option{--verbose}, except that @command{tar} generated the remaining lines
@iftex
(note the different font styles).
@end iftex
@ifinfo
.
@end ifinfo

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

@node short create
@subsection Short Forms with @samp{create}

As we said before, the @option{--create} (@option{-c}) operation is one of the most
basic uses of @command{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 @ref{Styles}; for now, here is what the
previous example (including the @option{--verbose} (@option{-v}) option) looks like
using short option forms:

@smallexample
$ @kbd{tar -cvf collection.tar blues folk jazz}
blues
folk
jazz
@end smallexample

@noindent
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:

@smallexample
$ @kbd{tar -cfv collection.tar blues folk jazz}
@end smallexample

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

@smallexample
$ @kbd{tar blues --create folk --file=collection.tar jazz}
@end smallexample

@noindent
is confusing as it is.  When shown using short forms, however, it
becomes much more so:

@smallexample
$ @kbd{tar blues -c folk -f collection.tar jazz}
@end smallexample

@noindent
It would be very easy to put the wrong string of characters
immediately following the @option{-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.

@node create dir
@subsection Archiving Directories

@cindex Archiving Directories
@cindex Directories, Archiving
You can archive a directory by specifying its directory name as a
file name argument to @command{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:

@smallexample
$ @kbd{cd ..}
$
@end smallexample

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

@smallexample
$ @kbd{tar --create --verbose --file=music.tar practice}
@end smallexample

@noindent
@command{tar} should output:

@smallexample
practice/
practice/blues
practice/folk
practice/jazz
practice/collection.tar
@end smallexample

Note that the archive thus created is not in the subdirectory
@file{practice}, but rather in the current working directory---the
directory from which @command{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 @command{tar}.  For example, you will probably
not be able to store your home directory in an archive by invoking
@command{tar} from the root directory; @xref{absolute}.  (Note
also that @file{collection.tar}, the original archive file, has itself
been archived.  @command{tar} will accept any file as a file to be
archived, regardless of its content.  When @file{music.tar} is
extracted, the archive file @file{collection.tar} will be re-written
into the file system).

If you give @command{tar} a command such as

@smallexample
$ @kbd{tar --create --file=foo.tar .}
@end smallexample

@noindent
@command{tar} will report @samp{tar: ./foo.tar is the archive; not
dumped}.  This happens because @command{tar} creates the archive
@file{foo.tar} in the current directory before putting any files into
it.  Then, when @command{tar} attempts to add all the files in the
directory @file{.} to the archive, it notices that the file
@file{./foo.tar} is the same as the archive @file{foo.tar}, and skips
it.  (It makes no sense to put an archive into itself.)  @GNUTAR{}
will continue in this case, and create the archive
normally, except for the exclusion of that one file.  (@emph{Please
note:} Other implementations of @command{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
@GNUTAR{}.  In general, it is wise to always place the archive outside
of the directory being dumped.

@node list
@section How to List Archives

@opindex list
Frequently, you will find yourself wanting to determine exactly what a
particular archive contains.  You can use the @option{--list}
(@option{-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
@file{collection.tar} that you created in the last section with the
command,

@smallexample
$ @kbd{tar --list --file=collection.tar}
@end smallexample

@noindent
The output of @command{tar} would then be:

@smallexample
blues
folk
jazz
@end smallexample

@noindent
The archive @file{bfiles.tar} would list as follows:

@smallexample
./birds
baboon
./box
@end smallexample

@noindent
Be sure to use a @option{--file=@var{archive-name}} (@option{-f
@var{archive-name}}) option just as with @option{--create}
(@option{-c}) to specify the name of the archive.

@xopindex{list, using with @option{--verbose}}
@xopindex{verbose, using with @option{--list}}
If you use the @option{--verbose} (@option{-v}) option with
@option{--list}, then @command{tar} will print out a listing
reminiscent of @w{@samp{ls -l}}, showing owner, file size, and so
forth.  This output is described in detail in @ref{verbose member listing}.

If you had used @option{--verbose} (@option{-v}) mode, the example
above would look like:

@smallexample
$ @kbd{tar --list --verbose --file=collection.tar folk}
-rw-r--r-- myself user 62 1990-05-23 10:55 folk
@end smallexample