pack (Unix)

File Format
Name	pack (Unix)
Ontology	Electronic File Formats Compression pack (Unix)
Extension(s)	.z
Wikidata ID	Q29650301

pack is a command in Unix-style operating systems to compress files using Huffman coding. Files normally have a lowercase .z extension, appended to their names including any other extension they may already have in their uncompressed versions, e.g., file.txt.z.

See also

• compress (Unix)
• compact (Unix)

Identification

Files begin with bytes 0x1F 0x1E.

The gzip source code mentions an "old pack format" that begins with 0x1F 0x1F.

See also compress (Unix)#The 0x1f compression family.

Software

• GNU gzip (decompression only) [Note: Broken in v1.6 - 1.8]
• Tenth Edition of Unix → v10src.tar.bz2 → cmd/pack/ - Source code
• illumos: pack, unpack - Source code
• https://github.com/koalaman/pack - A modern implementation in Haskell

References

• pack man page (MKS Toolkit)
• pack man page (IBM)
• An ode to pack: gzip’s forgotten decompressor