A GUIDE TO LINUX DATA COMPRESSION

Linux users are fortunate in that their systems are equipped with a variety of free data compression utilities. The two most common types of compression are lossless compression, in which all of the original file's data is preserved intact, and lossy compression, in which some of the original data is discarded.

UNIX systems are generally distributed with the compress command, which automatically assigns the .Z extension to compressed files. However, the use of this command is deprecated in the Linux community because compress uses the patented LZW algorithm. If you encounter a file compressed with the compress command, you can translate it to a nonpatented format (gzip) using the znew command, which is included with most Linux distributions.

On Linux systems, the standard compression utility is gzip, one of the many useful utilities created by the Free Software Foundation's GNU Project. Gzip uses the patent-free LZ77 algorithm. The gzip command automatically assigns the *.gz extension to compressed files. Also employing a patent-free algorithm is bzip, which is claimed to offer significantly faster performance. The bzip utility automatically assigns the *.bz2 extension to compressed files.

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Typically included with most Linux distributions are a variety of additional commands, which can come in very handy in certain situations. The gzexe utility compresses an executable file (a script or program) so that it automatically decompresses when it is executed. Note that the compressed executables take longer to launch. This command can be used to reduce the amount of disk space occupied by infrequently used executables. The zforce utility adds the .gz extension to any files in the working directory that were compressed with gzip but lack the correct extension.

Available from online software archives such as SunSITE are a variety of additional utilities that may come in handy, including macunpack (extracts files from Macintosh MacBinary archives) and unarj, which decompresses files compressed with the ARJ compression program (used on MS-DOS and Amiga systems).

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