mkShell vs. buildEnv?

I’ve seen examples of nix-shell environments, sometimes based on buildEnv, sometimes on mkShell; are there some important differences? Which one should I use and why?

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Let’s first take a look at buildEnv:

This is basically a wrapper around the builder.pl, and simply provides you with a bunch of symlinks. I’m not sure why you’d use it for a nix-shell, but it seems like some people like to put all their buildInputs through buildEnv to get a reference to all their dependencies within a single directory.

mkShell

This one is super simple compared to buildEnv and the one I use every day, all it does is provide some defaults for a stdenv.mkDerivation. So you don’t need to give it a src or name, all you really need is buildInputs, maybe a shellHook that runs when you enter the nix-shell, and any env variables you want.

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See also Nixpkgs issue 58624, " mkShell needs more documentation in the manual" for more info.