There are many books written on Perl. In fact, the current popularity of Perl is often credited to the original publication of Programming Perl, also known as “The Camel” (because of the animal on its cover), by Larry Wall and Randal Schwartz. The Camel is also published by O’Reilly & Associates. The Camel isn’t the best place to start if you’re just learning Perl from scratch, but it’s essential if you want to really understand Perl and not just dabble in it.
Other Perl books published by O’Reilly & Associates are Learning Perl (“The Llama”), Advanced Perl Programming, Perl Cookbook, Mastering Regular Expressions, Learning Perl on Win32 Systems, Mastering Perl/Tk, Perl for System Administration, Perl for Web Site Management, Mastering Algorithms with Perl, Programming the Perl DBI, Perl and XML, and CGI Programming with Perl.
There are also books from other publishers, of course. Standouts include Object-Oriented Perl and Elements of Programming with Perl, both published by Manning Press, and Effective Perl Programming and Network Programming with Perl, published by Addison-Wesley Longman.
 The third and most recent edition of Programming Perl is written by Larry Wall, Tom Christiansen, and Jon Orwant.