Therefore, to archive a group of files and compress the result, you can use the commands:
# tar cvf backup.tar /etc
# gzip -9 backup.tar
The result will be backup.tar.gz. To unpack this file, use the reverse set of commands:
# gunzip backup.tar.gz
# tar xvf backup.tar
Of course always make sure that you are in the correct directory before unpacking a tar file.
You can use some UNIX cleverness to do all of this on one command line, as in the following:
# tar cvf - /etc 
gzip -9c > backup.tar.gz
Here, we are sending the tar file to ``-'', which stands for tar's standard output. This is piped to gzip, which compresses the incoming tar file, and the result is saved in backup.tar.gz. The -c option to gzip tells gzip to send its output to stdout, which is redirected to backup.tar.gz.
A single command used to unpack this archive would be:
# gunzip -c backup.tar.gz 
tar xvf -
Again, gunzip uncompresses the contents of backup.tar.gz and sends the resulting tar file to stdout. This is piped to tar, which reads ``-'', this time referring to tar's standard input.
Happily, the tar command also includes the z option to automatically compress/uncompress files on the fly, using the gzip compression algorithm.
For example, the command
# tar cvfz backup.tar.gz /etc
is equivalent to
# tar cvf backup.tar /etc
# gzip backup.tar
Just as the command
# tar xvfz backup.tar.Z
may be used instead of
# uncompress backup.tar.Z
# tar xvf backup.tar
Refer to the man pages for tar and gzip for more information.