I think I'm on the right track now. I can see what was wrong with my original code, and I think that the structure you show above should be what I'm looking for.

Let me work on it some more (and re-read more carefully the relevant Perl documentation), then if I still have problems I'll either add another comment below or start a fresh post (I won't have much time to work on it until next week, however). Thanks for all your help.