gistfile1.txt

{ stdenv, lib, fetchurl}: stdenv.mkDerivation rec {
  name = "pkgname";
  version = "0.1";
  outputHashMode = "recursive";
  outputHashAlgo = "sha256";
  outputHash = "0v6a8x9hs9nyn3xih4fm6pp1s3si5vn9fkbb2817gcbmjln9zdz8"; # dummy, trying to obtain the real value by building the derivation
  phases = ["installPhase"];
  src = /directory;
  files = [
    "file1"
    "file2"
  ];

  installPhase = lib.concatMapStrings (file: ''
    install -Dm755 "$src/$file" "$out/$file"
  '') files;
}