In reply to @aftix:matrix.org
Is it possible to pin a flake's input to a specific package in nixpkgs? i.e. I would like to use a flake A from a "github:...", but A has an input B that points at another "github:...", and i'd like to point it at the pkgs.B i have in my environment.systemPackages instead

{ lib, stdenv, fetchurl, ...}:

stdenv.mkDerivation rec {
    name = "stereo_tool_gui_jack_64";
    version = "10.30";
    src = fetchurl {
        curlOpts = [ "-L" ];
        url = "https://www.stereotool.com/download/stereo_tool_gui_jack_64";
        sha = "b32d69b3892732548a55aa5241327afbc43bc7bd3f0a94548fb524596524ada2";
    };

    installPhase = ''
        mkdir -p $out/bin
        mkdir -p $out/share/applications
        cp $src $out/bin
    '';
}

In reply to @gdarends:matrix.org
I saved this file in my flake project. But how do I call this?

Where exactly do I add this? I added it to the modules but that returned an error.

....
nixosConfigurations = {
  nixos = nixpkgs.lib.nixosSystem {
    specialArgs = ....
    system = ....
    modules = [
    ]
.......
.....

outputs = { self, nixpkgs, nixpkgs-unstable }@inputs: 
  let
    system = "x86_64-linux";
    specialArgs = inputs // { inherit system; };
  in
  {
    nixosConfigurations = {
      audioproc1 = nixpkgs.lib.nixosSystem {
        specialArgs = specialArgs;
        system = system;
        modules = [ 
          ./hosts/audioproc1/configuration.nix
          ./nixosModules
          { packages.${system}.stereo_tool_gui_jack_64 = nixpkgs.legacyPackages.${system}.callPackage ./packages/stereo_tool_gui_jack_64.nix {}; }
        ];
      };
    };
  };

I did this, but I get an error that "packages" does not exist.

I did this:

preFixup = let
    libPath = lib.makeLibraryPath [
      xorg.libX11
      xorg.libXpm
      alsa-lib
      zlib
    ];
    in ''
      patchelf --set-interpreter "$(cat $NIX_CC/nix-support/dynamic-linker)" \
        --set-rpath "${libPath}" $out/bin/stereo_tool_gui_jack_64
    '';

But I'm getting an error of "No such file or directory"

It produces the following, which has a prefix for the file name.

and in the patchelf I'm referencing $out/bin/stereo_tool_gui_jack_64.

So I think there is a mismatch happening there.