Regular expressions. With a few weeks of learning the cryptic syntax you'll enjoy a lifetime of reaping its power. Mastering Regular Expressions by Friedl is

Regular expressions. With a few weeks of learning the cryptic syntax you'll enjoy a lifetime of reaping its power. Mastering Regular Expressions by Friedl is regarded as one of the best resources. But just to get up and running and as a reference I recommend http://regular-expressions.info http://regular-expressions.info