Perl.org free online Perl books: Impatient Perl
You write code for a living, and your inherit a legacy program written in Perl. You can program in your native language in your sleep. But you don't know Perl at all, or you've only dabbled with it. Your deadline doesn't give you enough time to rewrite the legacy program in your native language, but it needs new features. You need to learn Perl, and you need to learn it NOW. "Impatient Perl" was written for you.
This document is for people who either want to learn Perl or are already programming in Perl and just don't have the patience to scrounge for information to learn and use Perl. This document should also find use as a handy desk reference for some of the more common perl related questions.
In the mid 1980's, Larry Wall was working as a sysadmin and found that he needed to do a number of common, yet oddball functions over and over again. And he didn't like any of the scripting languages that were around at the time, so he invented Perl. Version 1 was released circa 1987. A few changes have occurred between then and now. The current version of Perl has exceeded 5.8.0 and is a highly recommended upgrade.