in reply to If I could only own one Perl book, it would be:
Because Beginning Perl is in my opinion a very good replacement for Camel, Llama, Alpaca together. As I myself don't need Perl books (I have perldoc and the interweb), I'd pick this book as the only one to own, and give it to someone who wants to learn the language.
Fortunately, you don't need it in dead tree form to read it, as it's available online, for free. That's the old edition, but still a great book for people who are capable of learning from concise instruction material.