Comment by ulbu

yes, i agree, nix should be considered the bible of bad documentations. it’s very bad at spotlighting the essentials and putting the non-essentials aside. it’s especially surprising for derivations, because nix is really, in the end, a frontend for building derivations. everything else converges on it.

and then i go to nix.dev and derivations are presented after fetchers? no surprise it’s so confusing, even though the concept is quite simple.

a derivation is a dict that is composed of (1) a shell script and (2) environment parameters it will have access to. a nix command will read the derivation, create the environment with only these parameters and execute the script. that’s it.

everything else about nix language is about building derivations. like copying files into its store. for example, evaluating “${pkgs.hello}” will be interpolated into a path. so in your derivation, you can define an env variable “hello = ${pkgs.hello}/bin” and it will be available in your script as “$hello” and will have the value of “/nix/store/<hash>-hello/bin”. nix will do the fetching and storing for you. so you can have “command $hello” in your script. neat!

play around with evaluating the ‘derivation’ built-in function.