File headers
Compression headers
Zip (.zip) format description, starts with 0x50, 0x4b, 0x03, 0x04 (unless empty — then the last two are 0x05, 0x06 or 0x06, 0x06)
Gzip (.gz) format description, starts with 0x1f, 0x8b, 0x08
xz (.xz) format description, starts with 0xfd, 0x37, 0x7a, 0x58, 0x5a, 0x00
zlib (.zz) format description, starts with (in bits) 0aaa1000 bbbccccc, where ccccc is chosen so that the first byte times 256 plus the second byte is a multiple of 31.
compress (.Z) starts with 0x1f, 0x9d
Gzip (.gz) format description, starts with 0x1f, 0x8b, 0x08
xz (.xz) format description, starts with 0xfd, 0x37, 0x7a, 0x58, 0x5a, 0x00
zlib (.zz) format description, starts with (in bits) 0aaa1000 bbbccccc, where ccccc is chosen so that the first byte times 256 plus the second byte is a multiple of 31.
compress (.Z) starts with 0x1f, 0x9d
