feat: add nix-update+nvd script

users/gandalf/modules/scripts/default.nix

@@ -0,0 +1,5 @@
+{ pkgs, nixosConfig, ... }: {
+  home.packages = [
+    (import ./nix-update.nix { inherit pkgs nixosConfig; })
+  ];
+}

users/gandalf/modules/scripts/nix-update.nix

@@ -0,0 +1,35 @@
+{ pkgs, nixosConfig }:
+
+pkgs.writeShellScriptBin "nuf" ''
+  reset="\e[0m"
+  red="\e[31m"
+  green="\e[32m"
+  yellow="\e[33m"
+  white_bold="\e[1;37m"
+
+  function error {
+    echo ""
+    echo -e "''${red}>>>Error: $1''${reset}"
+    exit 1
+  }
+
+  FLAKE=$(readlink -f /etc/nixos)
+
+  echo -e "''${green}>>> Updating flake $FLAKE ...''${reset}"
+  ${nixosConfig.nix.package}/bin/nix flake update --flake "$FLAKE" || error "Updating failed"
+
+  cd $(mktemp -d)
+  echo ""
+  echo -e "''${green}>>> Building configuration ...''${reset}"
+  nixos-rebuild build --flake "$FLAKE" || error "Building failed"
+
+  echo ""
+  echo -e "''${green}>>> Running diff ...''${reset}";
+  ${pkgs.nvd}/bin/nvd diff /run/current-system result || error "Diff failed"
+
+  cd - > /dev/null
+
+  echo ""
+  echo -e "''${yellow}>>> The new configuration has not been activated.''${reset}"
+  echo -e "''${yellow}>>> Use ''${white_bold}nixos-rebuild switch''${reset}''${yellow} to activate.''${reset}"
+''