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.
Files begin with bytes
The gzip source code mentions an "old pack format" that begins with
- GNU gzip [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 (write-only)