nix-wrap: shebang to make your Nix file into executable

nix-wrap

#!/usr/bin/env bash

#echo '$@ = ' "$@"

nixfile="$1"; shift
#echo "nixfile =" "$nixfile"

outpath="$(nix-build --pure $nixfile)"
#echo "outpath =" "$outpath"

[ $# -eq 0 ] && echo "Available subcommands:" $(ls "$outpath/bin") && exit 0

cmd="$1"; shift
#echo "cmd =" "$cmd"

#for ARG in "$@"; do
#    echo "ARG =" $ARG
#done

exec "$outpath/bin/$cmd" "$@"

venv.nix

#!/usr/bin/env nix-wrap

# Usages:
#$ ./venv.nix bash
#$ nix run -f ./venv.nix '' -- -c 'python --version'
#$ nix run -f ./venv.nix ''
#$ nix bundle -f ./venv.nix

let
  makeOverridable = f: f {} // { override = y: makeOverridable (x: f (x // y)); };
in
  makeOverridable ({ pkgs ? import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/c9a97ff47bb0db44f4a504015a5d1cedb3094c85.tar.gz") {} }:
    pkgs.buildFHSUserEnv {
      name = "bash";
      targetPkgs = pkgs: (with pkgs; [
        python37
        python37Packages.pip
        python37Packages.virtualenv
        pythonManylinuxPackages.manylinux2014Package
      ]);
      profile = ''
        python3 -m venv ${builtins.toString ./.venv-py37}
        source ${builtins.toString ./.venv-py37/bin/activate}
      '';
      runScript = "bash";
    }
  )