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To understand how to run tar in the three operating modes listed
previously, you also need to understand how to use two of the options to
tar: ‘--file’ (which takes an archive file as an argument)
and ‘--verbose’. (You are usually not required to specify
either of these options when you run tar, but they can be very
useful in making things more clear and helping you avoid errors.)
| The ‘--file’ Option | ||
| The ‘--verbose’ Option | ||
| Getting Help: Using the ‘--help’ Option |
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Specify the name of an archive file.
You can specify an argument for the ‘--file=archive-name’ (‘-f archive-name’) option whenever you
use tar; this option determines the name of the archive file
that tar will work on.
If you don’t specify this argument, then tar will examine
the environment variable TAPE. If it is set, its value will be
used as the archive name. Otherwise, tar will use the
default archive, determined at compile time. Usually it is
standard output or some physical tape drive attached to your machine
(you can verify what the default is by running tar
--show-defaults, see section Obtaining GNU tar default values). If there is no tape drive
attached, or the default is not meaningful, then tar will
print an error message. The error message might look roughly like one
of the following:
tar: can't open /dev/rmt8 : No such device or address tar: can't open /dev/rsmt0 : I/O error
To avoid confusion, we recommend that you always specify an archive file
name by using ‘--file=archive-name’ (‘-f archive-name’) when writing your tar commands.
For more information on using the ‘--file=archive-name’ (‘-f archive-name’) option, see
Choosing and Naming Archive Files.
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Show the files being worked on as tar is running.
‘--verbose’ (‘-v’) shows details about the results of running
tar. This can be especially useful when the results might not be
obvious. For example, if you want to see the progress of tar as
it writes files into the archive, you can use the ‘--verbose’
option. In the beginning, you may find it useful to use
‘--verbose’ at all times; when you are more accustomed to
tar, you will likely want to use it at certain times but not at
others. We will use ‘--verbose’ at times to help make something
clear, and we will give many examples both using and not using
‘--verbose’ to show the differences.
Each instance of ‘--verbose’ on the command line increases the verbosity level by one, so if you need more details on the output, specify it twice.
When reading archives (‘--list’, ‘--extract’,
‘--diff’), tar by default prints only the names of
the members being extracted. Using ‘--verbose’ will show a full,
ls style member listing.
In contrast, when writing archives (‘--create’, ‘--append’,
‘--update’), tar does not print file names by
default. So, a single ‘--verbose’ option shows the file names
being added to the archive, while two ‘--verbose’ options
enable the full listing.
For example, to create an archive in verbose mode:
$ tar -cvf afiles.tar apple angst aspic apple angst aspic
Creating the same archive with the verbosity level 2 could give:
$ tar -cvvf afiles.tar apple angst aspic -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic
This works equally well using short or long forms of options. Using long forms, you would simply write out the mnemonic form of the option twice, like this:
$ tar --create --verbose --verbose …
Note that you must double the hyphens properly each time.
Later in the tutorial, we will give examples using ‘--verbose --verbose’.
The ‘--verbose’ option also enables several warning messages, that tar does not issue otherwise, such as the warning about record size being used (see section The Blocking Factor of an Archive), selecting the decompress program and the like. If these are of no interest to you, you can suppress them using the ‘--warning’ option after ‘--verbose’, e.g.:
$ tar -c -v --warning=no-verbose -f afiles.tar apple angst aspic
See section verbose, for details.
The full output consists of six fields:
ls -l output (see Verbose listing in GNU core utilities).
Depending on the file type, the name can be followed by some additional information, described in the following table:
The file or archive member is a symbolic link and link-name is the name of file it links to.
The file or archive member is a hard link and link-name is the name of file it links to.
The archive member is an old GNU format long link. You will normally not encounter this.
The archive member is an old GNU format long name. You will normally not encounter this.
The archive member is a GNU volume header (see section Tape Files).
Encountered only at the beginning of a multi-volume archive (see section Using Multiple Tapes). This archive member is a continuation from the previous volume. The number n gives the offset where the original file was split.
An archive member of unknown type. c is the type character from
the archive header. If you encounter such a message, it means that
either your archive contains proprietary member types GNU tar is not
able to handle, or the archive is corrupted.
For example, here is an archive listing containing most of the special suffixes explained above:
V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header-- -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at byte 32456-- -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues
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The ‘--help’ option to tar prints out a very brief list of
all operations and option available for the current version of
tar available on your system.
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