native secret download

example.md

[clever@amd-nixos:~/nix-tests]$ nix repl --allow-unsafe-native-code-during-evaluation
Welcome to Nix version 2.0. Type :? for help.

nix-repl> import ./secret-download.nix
{ ... }; }

nix-repl> import ./secret-download.nix
{ downloader = «derivation /nix/store/vkvj32swicvjc3hya36p06q9lb60sp7g-downloader.drv»; foo = { ... }; }

nix-repl> (import ./secret-download.nix).foo
{ val1 = 25; val2 = "uid=1000(clever) gid=100(users) groups=100(users),1(wheel),72(vboxusers),131(docker),500(wireshark)"; }

secret-download.nix

with import <nixpkgs> {};

rec {
  downloader = writeScript "downloader" ''
    #!${stdenv.shell}
    echo "{val1 = 5 * 5; val2 = \"$(id)\"; } "
  '';
  foo = builtins.exec [ downloader ];
}