Regex is an acquired taste: initially bewildering and bitter, but given time it grows on you. Eventually you begin to appreciate its bouquet. Small, efficient, and powerful, Regex epitomizes good code. This is an advanced discussion of Regex I have found useful in Pipes. If you are new to either, then read up and play.
Other reference material includes Regular Expressions in Yahoo Pipes, but is a tad dated. Similarly. The Pipes forum is very helpful, especially hapdaniel.