(Shrug...)

“Perlish” or not, is it abundantly clear? With a suitable addition of comments, “I think so.”

What I'd really want to see, as “the unfortunate soul who's trying to pick-up after you, after you (poor thing...) got smooshed by that bread-truck,” is a nice, crystal-clear explanation of just exactly where you're headed with that concatenation: $pdu . ''.$pdu_num.''. Where am I gonna see that again? How is that value going to be used? If I needed to change the format of that string, what's gonna break?

You generally don't get Brownie points for being “clever,” nor even for being “efficient.” What enamors you(r memory) to your mourners co-workers is ... simple clarity.

“The computer is really, really fast. We know that.   I'm not (anymore).  ;-)  Don't make me try to ‘figure out’ what you were thinking, nor why.” Do that for me, and I shall forever say about you:   “Such a nice person. Too bad about that bread-truck...”