The UNIX operating system has several
integrated utilities that allow multiple files to be backed up and
compressed. The tar
(tape archive) command enables you to back up single or multiple files
in a directory hierarchy. The tar
command is standard with all
versions of the UNIX operating system. Although it was originally
developed for use with tape drives, tar
can copy files to other
locations on the hard disk or to a floppy disk and other removable
media. The tar
command can create an archive
from a single file, but it is primarily used to combine multiple
files, such as the contents of a directory, into a single file and
then extract them later if they are needed. By itself, it does not
compress the files as it bundles them like the zip/winzip programs for
PC's. The most frequently used options available with the tar
command are c, t, and
x. It is not necessary (but accepted) to precede these with a dash (-) as with
other UNIX command options. The command syntax is shown below. Roll
over Figure for an example with an explanation of the syntax.
Figure shows the functions (letters and modifiers) that are
used with the tar
command.
| Command Format: |
| tar function
[modifier] [output file] filename(s)/directory(s) |
Tar Functions:
- c (create) - used to archive
one or more files or directories to create an archive file.
Note: When specifying the name of the output file to be
created, be sure to specify a .tar extension so tar files can be easily distinguished from
others.
- t (table of contents) - used
to see a table of contents of the tar file. This is a listing of
the files that were combined to make the one tar file.
- x (extract) - used to extract
the file(s) from the archive and separate them into multiple files
again. The tar file still exists after this is done.
Function Modifiers:
- f (file) - allows you to
specify a tar file to Create (c), Extract from (x) or see the
Table of contents of (t).
- v (verbose) - modifier
executes the command in verbose mode which allows you to see the
detailed results of the tar
command as they occur.
Figure
illustrates some
examples using the tar
command. These are explained in
greater detail below.
- Example 1 - Archives all
files in the user1 directory to tape. If no file name (f) option
is specified, the default output device is tape (/dev/rmt/0 -
raw magnetic tape 0 is the first tape drive).
- Example 2 - Archives all
files and subdirectories in the dir2 to a tar file called dir2.tar
and places it in the /home/user2/backup directory. If you refer to
the class file tree, you will see that beans and recipes are
subdirectories whereas notes is a file. Any files in
subdirectories will also be included in the resulting tar file.
- Example 3 - Combines several
files to create an archive file called files.tar in the default
directory of the hard drive (usually your home directory).
- Example 4 - Views the table
of contents of the tar file in verbose mode which displays the
detail of the files including permission and size, etc.
- Example 5 - Archives three
files to the floppy disk for backup.
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Interactive
Media Activity
(Flash,
95 kB) |
| |
Archiving
files with tar
In
this media activity, you are logged in as user2
and your current working directory is:
/home/user2. Refer to the Class File Tree
Structure by clicking the 'tree' button located on
the Menu Bar and type the commands that would
accomplish the requested objectives.
Note: Be sure to press enter after each one. Click
on step 1 to begin. |
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