Index: Keywords/sample.ucl
===================================================================
--- Keywords/sample.ucl
+++ Keywords/sample.ucl
@@ -20,32 +20,39 @@
 
 actions: [file(1)]
 arguments: true
-post-install-lua: <<EOS
-  args = {}
-  for arg in string.gmatch("%@", "%S+") do
-    table.insert(args, arg)
+validation: <<EOS
+  if #arg == 1 then
+    if string.find(arg[1], "%.sample$") == nil then
+      io.stderr:write("only 1 or 2 arguments are allowed")
+      os.exit(1)
+    fi
+  elif #arg == 2 then
+    if arg[1] == arg[2] then
+      io.stderr:write("2 identical arguments provided")
+      os.exit(1)
+    fi
+  else
+    io.stderr:write("only 1 or 2 arguments are allowed")
+    os.exit(1)
   end
-  sample_file = pkg.prefixed_path(args[1])
-  if args[2] == nil then
-    target_file = string.gsub(sample_file,'%.sample$', "")
+EOS
+post-install-lua: <<EOS
+  sample_file = pkg.prefixed_path(arg[1])
+  if #arg == 2 then
+    target_file = pkg.prefixed_path(arg[2])
   else
-    target_file = pkg.prefixed_path(args[2])
+    target_file = string.gsub(sample_file,'%.sample$', "")
   end
   if not pkg.stat(target_file) then
     pkg.copy(sample_file, target_file)
   end
 EOS
-
 pre-deinstall-lua: <<EOS
-  args = {}
-  for arg in string.gmatch("%@", "%S+") do
-    table.insert(args, arg)
-  end
-  sample_file = pkg.prefixed_path(args[1])
-  if args[2] == nil then
-    target_file = string.gsub(sample_file,'%.sample$', "")
+  sample_file = pkg.prefixed_path(arg[1])
+  if #arg == 2 then
+    target_file = pkg.prefixed_path(arg[2])
   else
-    target_file = pkg.prefixed_path(args[2])
+    target_file = string.gsub(sample_file,'%.sample$', "")
   end
   if pkg.filecmp(sample_file, target_file) == 0 then
     os.remove(target_file)