Nar in bash

gistfile1.txt

let
  some-derivation = derivation {
    name = "hello-world";
    system = "x86_64-linux";
    builder = "/bin/sh";
    args = ["-c" "echo hello world > $out"];
  };
  a = derivation {
  name = "something.nar";
  builder = "/bin/sh";
  system = "x86_64-linux";
  args = ["-c" ''
    str(){
      len=''${#1}
      padlen=$(( (8 - (len % 8)) % 8  ))
      int $len
      printf "%s" "$1"
      pad $padlen
    }
    int(){
      x="$(printf "%016x" "$1")"
      rev=
      while read -n 2 a; do
        rev="$(printf '%s ' "$a" "$rev")"
      done <<EOF
      $(printf "$x")
    EOF
      rev="$(printf "\x%s " $rev)"
      printf "%b" $rev
    }
    pad(){
      x="$(printf %-''${1}s "")"
      printf "''${x// /$(printf "%s" "\x0")}"
    }

    {
    str nix-archive-1
    str "("
      str "type"
      str "directory"

      str "entry"
      str "("
        str "name"
        str "some-binary"
        str "node"
        str "("
          str "type"
          str "symlink"
          str "target"
          str "${some-derivation}"
        str ")"
      str ")"

      str "entry"
      str "("
        str "name"
        str "some-binary-2"
        str "node"
        str "("
          str "type"
          str "regular"
          str "executable" ; str ""
          str "contents"
          str "some-binary-contents"
        str ")"

      str ")"
    str ")"
    } >> $out
  ''];
};
in
derivation {
  name = "unpacker";
  builder = "builtin:fetchurl";
  outputHashMode = "flat";
  system = "no-system";
  unpack = true;
  url = "file://${a}";
}