Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

You should definitely use version 5. Version 4 is old, limited, and no longer maintained; its last patch (4.036) was in 1992. The most recent production release is 5.005_01. Further references to the Perl language in this document refer to this production release unless otherwise specified. There may be one or more official bug fixes for 5.005_01 by the time you read this, and also perhaps some experimental versions on the way to the next release.