NOTE: This is a repost of an entry that I wrote for the molecularecologist.com.
Regular expressions are something that pretty much everyone working with more than a handful of data should take the time to learn (a handful being around 500 lines). They can easily improve your life, particularly if you've ever had to make multiple, mind-numbing changes over more than about 50 lines of an excel file, for instance. They can also be terribly frustrating to learn and often are similar in appearance to Sumerian for the uninitiated. All that's changing - Zed Shaw's excellent series of books now delves into regular expression territory (the tutorials for other languages are also very, very good), and it's a learning exercise that's worth looking into (keep in mind that this is an early "alpha" version that is evolving):
Decent knowledge of regular expressions combined with a very good text editor and perhaps a data manipulation tool can fundamentally change the way you work, increase repeatability, and improve your science.