compress (Unix)

File Format
Name	compress (Unix)
Ontology	Electronic File Formats Compression compress (Unix)
Extension(s)	.Z
MIME Type(s)	application/x-compress
Wikidata ID	Q29209269
Released	~1984

This article is about a specific file format. For compression in general, see Compression.

compress is a Unix command line utility, and a general-purpose compressed file format. Its compression algorithm is based on LZW.

Identifiers

The conventional filename extension is a capitalized .Z.

Identification

Files begin with bytes 1f 9d.

See also

• SCO compress LZH - variant
• Quasijarus Strong Compression - variant
• pack (Unix) - predecessor
• compact (Unix) - predecessor
• Squash (RISC OS)

Formats that could be considered to be the successors of compress include Freeze/Melt, and (especially) Gzip.

The 0x1f compression family

There are several compressed file formats, with similar features, that begin with byte value 0x1f (octal 037; decimal 31). We arbitrarily choose compress as the representative example, and list the formats here.

Signature (hex)	Format
1f 1e	pack (Unix)
1f 1f	pack (Unix) - old format
1f 8b	gzip
1f 9d	compress
1f 9e	Freeze/Melt - old format
1f 9f	Freeze/Melt - new format
1f a0	SCO compress LZH
1f a1	Quasijarus Strong Compression
1f ff or ff 1f	compact (Unix)

Software

• ncompress
• Gzip can uncompress .Z files.
• 7-Zip
• liblzw
• Windows port of Compress utility
• Deark

External links

• Wikipedia article