How to run shell commands when initializing nix-shell

{ pkgs ? import <nixpkgs> {} }:

with pkgs;

stdenv.mkDerivation {
  name = "substrate";
  buildInputs = [
    llvmPackages.libclang
    binaryen
  ];

  shellHook = "export LIBCLANG_PATH=${llvmPackages.libclang}/lib";
}