How do I unpack a compressed tar file

Unzipping a .gz file

gunzip filename.tar.gz

This replaces filename.tar.gz with filename.tar

Extracting tar files

tar xvf filename.tar

Note: Always move to an empty directory before unpacking a tarfile. When you unpack a tarfile its contents are written to the current directory. Any file or directory with the same name as the contents of the tarfile will be overwritten!

A quick method

Alternatively, you can unpack a compressed/zipped tarfile using the zcat or gzcat command. (gzcat is a local alias for the GNU zcat command). This leaves the compressed .Z or .gz tarfile intact. For example:

zcat filename.tar.Z  | tar xvf -

or

gzcat filename.tar.gz | tar xvf -

The zcat command recreates the uncompressed tarfile, which is then piped into the tar command to extract the files.

Source: http://info.eps.surrey.ac.uk/FAQ/unpack.html