gistfile1.txt

{ tmpdir ? "/custom-tmp"
}:
{
  custom_nix = pkgs.stdenv.mkDerivation {
    name = "nix-with-custom-tmpdir";
    buildInputs = [ pkgs.makeWrapper ];
    installPhase = ''
      mkdir -p $out/bin
      for script in ${pkgs.nix}/*; do
        ln -s $script $out/bin
      done
      for script in $out/bin/*; do
        wrapProgram $script --set TMPDIR "${tmpdir}" 
      done
    '';
  };
}