nix.sh

#! /usr/bin/env nix-shell
#! nix-shell -i python27 shell.nix
print "Hello world"

shell.nix

with import <nixpkgs> {};
stdenv.mkDerivation rec {
  name = "env";
  env = buildEnv { name = name; paths = buildInputs; };
  buildInputs = [
    python
    python27Packages.virtualenv
    python27Packages.pip
    libffi
    openssl
    moreutils
    ruby
    curl
  ];
}