Until 23:59 Pacific Time 9/Aug/2012, O' Reilly at
http://shop.oreilly.com/category/deals/perl-owo.do?code=WKPER5 are offering 50% off a range of PERL e-books. (For those unfamiliar with PERL it is the Practical Extraction and Reporting Language)
"Whether you are just starting out in Perl or making the leap from easy to complex tasks, get a
clear roadmap for improving your skills with these titles from O'Reilly.
E-books from O' Reilly.com are DRM-free. You get free lifetime access, multiple file formats, and free updates.
Use discount code
WKPER5 - Deal expires August 9, 2012 at 11:59pm PT, and cannot be combined with other offers."
The regular expressions book is of particular interest as it covers variations between regular expressions under Dot Net and other environments.