We'll presume that you've already read Learning Perl, or at least pretend you have, and that you've played enough with Perl to already have those basics down. For example, you won't see an explanation in this book that shows how to access the elements of an array or return a value from a subroutine.
Make sure you know the following things:
How to run a Perl program on your system
Control structures such as while, if, for, and foreach
Perl operators such as grep, map, sort, and print
File manipulation such as open, file reading, and -x (file tests)
You might pick up deeper insight into these topics in this book, but we're going to presume you know the basics.