The compress command is used to reduce the size of a file
to approximately one-third its original size. This can be useful
to reduce the size of .tar files (which can become extremely large)
as well as any other large file that you aren't currently using
but need to keep online. The format of the compress command
is simple:
compress <filename>
This produces a file with the same name as the original, but with a .Z
extension. Unlike the tar command, which archives without deleting
the target directory, compress replaces the original file with
the compressed version.
To restore a compressed file to its original uncompressed state:
uncompress <filename>