How do I unpack a compressed tar file
( files ending in *.tar.Z or *.tar.gz )?

When downloading files from FTP archives, you will find that they are normally of the form filename.tar.Z or filename.tar.gz These files have been archived then compressed or zipped.

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Uncompressing a .Z file

Files ending in .Z have been compressed using the compress command. Compressed files can be restored to their original form using the uncompress command. Type:

        uncompress filename.tar.Z 

This replaces filename.tar.Z with filename.tar

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Unzipping a .gz file

Files ending in .gz have been compressed using the gzip command. Zipped files can be restored to their original form using the gunzip command. Type:

         gunzip filename.tar.gz 

This replaces filename.tar.gz with filename.tar

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Extracting tar files

The tar command is used for packing several files or even a whole directory into a single tarfile.

To unpack a tar file, type:

         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!

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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.

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M.Stonebank@ee.surrey.ac.uk

10th November 1994