tar.texi

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@command{tar} archives with tape drives.

@FIXME{this is a cop out.  need to add some simple tape drive info.}
@end itemize

@node stylistic conventions
@section Stylistic Conventions

In the examples, @samp{$} represents a typical shell prompt.  It
precedes lines you should type; to make this more clear, those lines are
shown in @kbd{this font}, as opposed to lines which represent the
computer's response; those lines are shown in @code{this font}, or
sometimes @samp{like this}.

@c When we have lines which are too long to be
@c displayed in any other way, we will show them like this:

@node basic tar options
@section Basic @command{tar} Operations and Options

@command{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 @command{tar} fall into one of two classes:
operations, and options.

Some arguments fall into a class called @dfn{operations}; exactly one of
these is both allowed and required for any instance of using @command{tar};
you may @emph{not} specify more than one.  People sometimes speak of
@dfn{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 @dfn{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 @command{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 @command{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 @GNUTAR{} for compatibility with Unix
@command{tar}.  In this book we present a full discussion of this way
of writing options and operations (@pxref{Old Options}), and we discuss
the other two styles of writing options (@xref{Long Options}, and
@pxref{Short Options}).

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 @command{tar} commands easier.
For example, instead of typing

@smallexample
@kbd{tar --create --verbose --file=afiles.tar apple angst aspic}
@end smallexample

@noindent
you can type
@smallexample
@kbd{tar -c -v -f afiles.tar apple angst aspic}
@end smallexample

@noindent
or even
@smallexample
@kbd{tar -cvf afiles.tar apple angst aspic}
@end smallexample

@noindent
For more information on option syntax, see @ref{Advanced tar}.  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, @emph{optional} ``options'' in certain
general class statements.  For example, we just talked about ``short and
long forms of options and operations''.  However, experienced @command{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 @command{tar} ``commands''.
A @command{tar} @dfn{command} is the entire command line of user input
which tells @command{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 @command{tar} command''.  When
the word ``command'' is used specifically like this, a person is usually
referring to the @command{tar} @emph{operation}, not the whole line.
Again, use context to figure out which of the meanings the speaker
intends.

@node frequent operations
@section The Three Most Frequently Used Operations

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.

@table @option
@item --create
@itemx -c
Create a new @command{tar} archive.
@item --list
@itemx -t
List the contents of an archive.
@item --extract
@itemx -x
Extract one or more members from an archive.
@end table

@node Two Frequent Options
@section Two Frequently Used Options

To understand how to run @command{tar} in the three operating modes listed
previously, you also need to understand how to use two of the options to
@command{tar}: @option{--file} (which takes an archive file as an argument)
and @option{--verbose}.  (You are usually not @emph{required} to specify
either of these options when you run @command{tar}, but they can be very
useful in making things more clear and helping you avoid errors.)

@menu
* file tutorial::
* verbose tutorial::
* help tutorial::
@end menu

@node file tutorial
@unnumberedsubsec The @option{--file} Option

@table @option
@xopindex{file, tutorial}
@item --file=@var{archive-name}
@itemx -f @var{archive-name}
Specify the name of an archive file.
@end table

You can specify an argument for the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option whenever you
use @command{tar}; this option determines the name of the archive file
that @command{tar} will work on.

@vrindex TAPE
If you don't specify this argument, then @command{tar} will examine
the environment variable @env{TAPE}.  If it is set, its value will be
used as the archive name.  Otherwise, @command{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 @kbd{tar
--show-defaults}, @pxref{defaults}).  If there is no tape drive
attached, or the default is not meaningful, then @command{tar} will
print an error message.  The error message might look roughly like one
of the following:

@smallexample
tar: can't open /dev/rmt8 : No such device or address
tar: can't open /dev/rsmt0 : I/O error
@end smallexample

@noindent
To avoid confusion, we recommend that you always specify an archive file
name by using @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) when writing your @command{tar} commands.
For more information on using the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option, see
@ref{file}.

@node verbose tutorial
@unnumberedsubsec The @option{--verbose} Option

@table @option
@xopindex{verbose, introduced}
@item --verbose
@itemx -v
Show the files being worked on as @command{tar} is running.
@end table

@option{--verbose} (@option{-v}) shows details about the results of running
@command{tar}.  This can be especially useful when the results might not be
obvious.  For example, if you want to see the progress of @command{tar} as
it writes files into the archive, you can use the @option{--verbose}
option.  In the beginning, you may find it useful to use
@option{--verbose} at all times; when you are more accustomed to
@command{tar}, you will likely want to use it at certain times but not at
others.  We will use @option{--verbose} at times to help make something
clear, and we will give many examples both using and not using
@option{--verbose} to show the differences.

Each instance of @option{--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 (@option{--list}, @option{--extract},
@option{--diff}), @command{tar} by default prints only the names of
the members being extracted.  Using @option{--verbose} will show a full,
@command{ls} style member listing.

In contrast, when writing archives (@option{--create}, @option{--append},
@option{--update}), @command{tar} does not print file names by
default.  So, a single @option{--verbose} option shows the file names
being added to the archive, while two @option{--verbose} options
enable the full listing.

For example, to create an archive in verbose mode:

@smallexample
$ @kbd{tar -cvf afiles.tar apple angst aspic}
apple
angst
aspic
@end smallexample

@noindent
Creating the same archive with the verbosity level 2 could give:

@smallexample
$ @kbd{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
@end smallexample

@noindent
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:

@smallexample
$ @kbd{tar --create --verbose --verbose @dots{}}
@end smallexample

@noindent
Note that you must double the hyphens properly each time.

Later in the tutorial, we will give examples using @w{@option{--verbose
--verbose}}.

@anchor{verbose member listing}
The full output consists of six fields:

@itemize @bullet
@item File type and permissions in symbolic form.
These are displayed in the same format as the first column of
@command{ls -l} output (@pxref{What information is listed,
format=verbose, Verbose listing, fileutils, GNU file utilities}).

@item Owner name and group separated by a slash character.
If these data are not available (for example, when listing a @samp{v7} format
archive), numeric @acronym{ID} values are printed instead.

@item Size of the file, in bytes.

@item File modification date in ISO 8601 format.

@item File modification time.

@item File name.
If the name contains any special characters (white space, newlines,
etc.) these are displayed in an unambiguous form using so called
@dfn{quoting style}.  For the detailed discussion of available styles
and on how to use them, see @ref{quoting styles}.

Depending on the file type, the name can be followed by some
additional information, described in the following table:

@table @samp
@item -> @var{link-name}
The file or archive member is a @dfn{symbolic link} and
@var{link-name} is the name of file it links to.

@item link to @var{link-name}
The file or archive member is a @dfn{hard link} and @var{link-name} is
the name of file it links to.

@item --Long Link--
The archive member is an old GNU format long link.  You will normally
not encounter this.

@item --Long Name--
The archive member is an old GNU format long name.  You will normally
not encounter this.

@item --Volume Header--
The archive member is a GNU @dfn{volume header} (@pxref{Tape Files}).

@item --Continued at byte @var{n}--
Encountered only at the beginning of a multi-volume archive
(@pxref{Using Multiple Tapes}).  This archive member is a continuation
from the previous volume. The number @var{n} gives the offset where
the original file was split.

@item  unknown file type @var{c}
An archive member of unknown type. @var{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 @GNUTAR{} is not
able to handle, or the archive is corrupted.
@end table

@end itemize

For example, here is an archive listing containing most of the special
suffixes explained above:

@smallexample
@group
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
@end group
@end smallexample

@smallexample
@end smallexample

@node help tutorial
@unnumberedsubsec Getting Help: Using the @option{--help} Option

@table @option
@opindex help
@item --help

The @option{--help} option to @command{tar} prints out a very brief list of
all operations and option available for the current version of
@command{tar} available on your system.
@end table

@node create
@section How to Create Archives
@UNREVISED

@cindex Creation of the archive
@cindex Archive, creation of
One of the basic operations of @command{tar} is @option{--create} (@option{-c}), which
you use to create a @command{tar} archive.  We will explain
@option{--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
@emph{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
@file{blues}, @file{folk}, and @file{jazz}.  The archive is called