in reply to book vs. web for Perl Regex study?
If you are just beginning with Regex, you should try the 'Regex Coach'.
It's a nice little piece of software, free, written in Lisp, and least compatible with Perl 5.6.
Very 'pedagogic' :)
For Win32:
http://weitz.de/files/regex-coach.exe
And for linux:
http://weitz.de/files/regex-coach.tgz
In Section
Seekers of Perl Wisdom