[clever@amd-nixos:~]$ nix-repl
Welcome to Nix version 1.11.4. Type :? for help.

nix-repl> :l <nixpkgs>
Added 6841 variables.

nix-repl> builtins.unsafeGetAttrPos "fetchurl" pkgs
{ column = 3; file = "/nix/store/k984k6xncihdsiajy99wk82gn3zhhy7x-nixos-17.03pre95306.a24728f/nixos/pkgs/top-level/all-packages.nix"; line = 188; }