One key task you will face over and over is matching particular patterns of text. The match might be as simple as finding one instance of a specific string in a body of text, or it could be much more complicated. A great tool for matching text is the language of regular expressions. A regular expression is an abstract way of expressing certain types of string-matching patterns.
Contrary to popular belief, regular expressions can't match everything you might want to match. They're limited to certain types of matches, and depending on the particular flavor of regular expression implementation, they could have a little more or a little less power. As an academic exercise, one might try to characterize exactly what you can match and what you can't. It's a very interesting endeavor that cuts to the very core of theoretical computer science...
