As compressors go, zstd is awesome. It's very fast while beating any commonly used alternative except xz in compression ratio. But alas, its command-line tool leaves much to be wished for:

• its package takes over 2MB, 1.2MB for the main executable
• it fails to remove files it's done with
• its compression levels use a different scale than the rest of the world (1..19 sometimes 22 instead of 1..9)
• turning off its chattiness makes you lose warnings

The first bit is a blocker towards making that tool a guaranteed (“essential”) part of a Linux distribution — it'd bloat the size of minimal systems (eg. containers) too much.

The other bits sometimes interfere with making zstd a drop-in replacement: in most places you can insert arbitrary arguments but it's not always the case.

On the other hand, libzstd is already essential! And while we're here, there's three other essential compressor libraries: zlib libbz2 liblzma (xz). Why not provide all four from a single small binary?

Thus, let's unify popular compressors and avoid weirdness of their command-line tools.

• zst
• xz
• gz
• bz2

This tool should be considered of beta quality.

• guess algorithm via header
• threaded [de]compression
• threading when multiple files
• sparse files
• io optimizations
• decent test coverage
• dlopen non-essential compressors?
• behave according to argv[0]
• --rsyncable