In my book I provide examples of using the sed editor on Unix and Linux systems to manipulate text with regular expressions. I've received email from several people wanting to learn more about Regular Expressions so I have provided some helpful information below...
In computing, regular expressions provide a concise and flexible means for identifying strings of text of interest, such as particular characters, words, or patterns of characters. Regular expressions (abbreviated as regex or regexp, with plural forms regexes, regexps, or regexen) are written in a formal language that can be interpreted by a regular expression processor, a program that either serves as a parser generator or examines text and identifies parts that match the provided specification.
Click here to learn more about Regular Expressions.
I also highly recommend the Regular Expressions Cookbook.