Datasheet

21
Working with the Shell
and standard error are saved to one file named alloutput if you append >&
alloutput. Finally, to append the output of a command to an already existing
file, the command must be followed by » instead of a single >.
21.1.8 Archives and Da ta Compression
Now that you have already created a number of files and directories, consider the
subject of archives and data compression. Suppose you want to have the entire
test directory packed in one file that you can save on a floppy disk as a backup
copy or send by e-mail. To do so, use the command tar (for tape archiver). With
tar --help, view all the options for the tar command. The most important of
these options are explained here:
-c (for create) Create a new archive.
-t (for table) Display the contents of an archive.
-x (for extract) Unpack the archive.
-v (for verbose) Show all files on screen while creating the archive.
-f (for file) Choose a file name for the archive file. When creating an archive,
this option must always be given as the last one.
To pack the test directory with all its files and subdirectories into an archive
named testarchive.tar, use the options -c and -f. For the testing purposes
of this example, also add -v to follow the progress of the archiving, although this
option is not mandatory. After using cd to change to your home directory where
the test directory is located, enter tar -cvf testarchive.tar test. After
that, view the contents of the archive file with tar -tf testarchive.tar.
The test directory with all its files and directories has remained unchanged on
your hard disk. To unpack the archive, enter tar -xvf testarchive.tar,
but do not try this yet.
For file compression, the obvious choice on Linux is the popular gzip pro-
gram. Just enter gzip testarchive.tar. With ls, now see that the file
testarchive.tar is no longer there and that the file testarchive.tar.gz
has been created instead. This file is much smaller and therefore much better
suited for transfer via e-mail or storage on a floppy.
Now, unpack this file in the test2 directory created earlier. To do so, en-
ter cp testarchive.tar.gz test2 to copy the file to that directory.
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