Am I depending on a quirk, which might go away in a future version of perl? In particular, will this method work in a linux context also?

Your are using a Perl version that hasn't been updated or supported in 10 years. Many of us here are willing to discuss the general strategies of using global variables, modules, object orientation and so on. But when it comes to bugs and quirks in your ancient version of Perl (on an operating system that's nearly end-of-life), you are pretty much on your own.

Personally, i refuse to support Perl versions or operating system that are end-of-life and don't receive security updates (with the explicit exceptions of Retro-Computing, historical exibits and emulators). I mean, who knows in this day and age. If i help you keep an insecure system running, i might be legally liable and your companies lawyers might come after me in the worst case if there's a data breach through a known security problem in your system. If you upgrade and you run into compatibility problems, that is another matter entirely. I'm pretty sure many of us here would be more than happy to help with specific problems, if you ask a proper, specific question: How do I post a question effectively?