Okay, I'm logged in now. Posted this question anonymously by accident. I found some answers here:

http://docstore.mik.ua/orelly/perl/prog3/ch04_04.htm
4.4.4. Loop Control

But I still don't understand how to use the label and next commands to solve my problem. I think it would go kind of like this:

Start loop A, get a line.
Start loop B, get a line.
B doesn't match A so print a blank line.
Go to the next iteration of loop A.
Start loop B, get a line.
Now A and B match, so print out B.
Go to the next iteration of loop A.
Start loop B, get a line.
[download]

I think that's how the whole "next" idea works. But what I really want is not that. I don't want it to start loop B over every time. I want it to hold its place in loop B. Can I do that?