pkgs.stdenv.mkDerivation {
  name = "on-modify";
  src = "${pkgs.timewarrior}/share/doc/timew/ext";
  buildInputs = [ pkgs.python ];
  patchPhase = ''
    head -n 1 $src/on-modify.timewarrior
    patchShebangs $src
    head -n 1 $src/on-modify.timewarrior
  '';
  installPhase = ''
    mkdir $out
    cp $src/on-modify.timewarrior $out/
  '';
}