It would be really cool if kbd would link against the compression libs directly instead of shelling out. Shelling out produces all kinds of packaging problems in Nixpkgs/NixOS:

• We need to have /bin/sh which we don't necessarily want
• We need to include the binary outputs of the compression tools instead of the lib outputs in kbd

Is that something you could consider? It would make the kbd closure a little smaller and solve all sorts of headaches on our side without making life any harder for others (distro packagers).