Added all this in pure Lua. ;)

lua/test.lua

@@ -0,0 +1,26 @@
+#!/usr/bin/env lua
+
+-- This file is part of chkgrp that is a program that checks if a user is a
+-- member of a group.
+--
+-- Author: Johannes Findeisen <you@hanez.org> - 2025
+-- Homepage: https://git.xw3.org/hanez/chkgrp
+-- License: Apache-2.0 (see LICENSE)
+
+local checkgroup = require("checkgroup")
+
+local user = arg[1]
+local group = arg[2]
+
+local result = checkgroup.is_user_in_group(user, group)
+
+if result == true then
+    print("Yes")
+    os.exit(0)
+elseif result == false then
+    print("No")
+    os.exit(1)
+else
+    os.exit(2)
+end
+