build.sh

#!/usr/bin/env bash
set -e

darwin-rebuild switch --arg configuration "$(hostname -s).nix"

configuration.nix

{ config, lib, pkgs, ... }:

with lib;

let
  host = config.networking.hostName;
in

{
  environment.systemPackages = mkIf (host == "foo") [
    curl
  ];

  nix.nixPath = [ "darwin-config=${./. + host}.nix" ];
}

foo.nix

{
  imports = [ ./configuration.nix ];
  networking.hostName = "foo";
}