You will also want to read the perl5 porter FAQ and the perlhacktut is also a valuable reference for hacking the core.

For a program as large as perl, just reading the source in one go is just overwhelming and is not going to teach you much. I recommend looking at just one aspect, say a single perl function, and figure out where it resides and how it is built into the rest of the program. You will quickly get a feel for the general flow of perl, if not all the details, and this will allow you to bootstrap yourself to a level such that you can start making some changes. If you really get into it, I recommend joining p5p and searching their archives at p5p archives .

Good luck!

-Mark