compress

Compress files

$ compress path/to/file1 path/to/file2

$ compress -f path/to/file

$ compress -b 12 path/to/file

$ compress -c path/to/file

$ compress -d path/to/file.Z

$ compress -v path/to/file

$ compress -k path/to/file

compress [-fkvcV] [-b bits] [file...]

compress is the classic Unix compression utility that implements the LZW (Lempel-Ziv-Welch) algorithm, producing files with the distinctive .Z extension. It was the standard compression tool on Unix systems before being largely superseded by gzip in the early 1990s. The algorithm uses adaptive dictionary-based compression, starting with 9-bit codes and expanding up to 16 bits as needed.
When compressing files, compress preserves important file metadata including ownership, permissions (modes), and timestamps. It operates safely by default, refusing to compress symbolic links and files with multiple hard links unless the -f force flag is used. Compressed files replace the originals unless the -c stdout option or -k keep option is specified.
The compression ratio varies by file type, with text files typically achieving 50-60% size reduction. Binary files may compress less effectively. While compress is considered obsolete for most purposes today, it remains available for compatibility with legacy .Z archives and systems that still use this format. Modern alternatives like gzip and bzip2 provide better compression ratios and are more widely supported.

-f

Force compression, overwriting existing files and compressing files with hard links

Keep (do not delete) input files

Verbose mode; display compression percentage for each file

Write output to stdout without modifying any files

Print version and patchlevel information

Operate recursively through directories

Set maximum bits per code (9-16, default 16)

Stop parsing options; treat remaining arguments as filenames

The program uses a modified Lempel-Ziv algorithm starting with 9-bit codes. Typical compression achieves 50-60% reduction for text files. Exit status is 0 for success, 2 if output would be larger than input, and 1 for errors. Use -b12 for compatibility with older systems.

compress implements the classic Unix LZW compression algorithm. While largely superseded by gzip and other modern compressors, it remains available for compatibility and for processing .Z files.

uncompress(1), gzip(1), bzip2(1), zcat(1)