12.3 Backing Up, Compressing, and Restoring Files
12.3.2 Compressing files
It is frequently useful to archive files that have not been used for a while and then compress them so they take up less disk space. Any file, including those archives created with tar, can be compressed. Compression is a valuable tool since it reduces the amount of disk space files occupy while still keeping them readily available. The compress command is used to compress files and is included with all versions of the UNIX operating system. The compress utility uses a special format to reduce the size of the file anywhere from 20 percent to 80 percent depending on the type of file. If the compress utility determines that the file cannot be compressed or that there will be no reduction in file size, the file will remain unchanged.

When files are compressed with the compress command, the existing file is replaced using the same name but with a .Z suffix appended. Note that this is an uppercase letter Z. The Figure shows an example of the compress command with the verbose (-v) option. This will show the name of the input (bin.file) and output file (bin.file.Z) and the amount of compression achieved. Use the ls -l (list long) command before compressing a file to see its original size in bytes and then again afterward to see the compressed size. Multiple files can be compressed simultaneously and wildcard metacharacters are supported.

Command Format:
compress option file1 file2