grandperspective: add update script

pkgs/by-name/gr/grandperspective/package.nix

@@ -4,6 +4,11 @@
   fetchurl,
   undmg,
   makeWrapper,
+  writeShellApplication,
+  curl,
+  cacert,
+  gnugrep,
+  common-updater-scripts,
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -29,6 +34,21 @@ stdenv.mkDerivation (finalAttrs: {
     makeWrapper "$out/Applications/GrandPerspective.app/Contents/MacOS/GrandPerspective" "$out/bin/grandperspective"
   '';
 
+  passthru.updateScript = lib.getExe (writeShellApplication {
+    name = "grandperspective-update-script";
+    runtimeInputs = [
+      curl
+      cacert
+      gnugrep
+      common-updater-scripts
+    ];
+    text = ''
+      url="https://sourceforge.net/p/grandperspectiv/documentation/ci/master/tree/CHANGES.txt?format=raw"
+      version=$(curl -s "$url" | grep -oP 'Version \K[0-9.]+(?=,)' | head -n 1)
+      update-source-version grandperspective "$version"
+    '';
+  });
+
   meta = with lib; {
     description = "Open-source macOS application to analyze disk usage";
     longDescription = ''