in reply to Better way to define global variables
In addition to what choroba said, I am getting the same error as you are (although you didn't state it in your question, just in the CB): Global symbol "$SYS_DIR" requires explicit package name. Obviously I am missing something in the documentation. Adding strictures/warnings does not seem to help identify the problem.
Update: The key was explicitly importing the import method with the use Exporter 'import' line. I missed it in my initial reading. Apply choroba's changes and you should be set.