This book is about a powerful tool called ™regular expressionsš. It teaches you how to use regular expressions to solve problems and get the most out of tools and languages that provide them. Most documentation that mentions regular expressions doesn't even begin to hint at their power, but this book is about mastering regular expressions. Regular expressions are available in many types of tools (editors, word processors, system tools, database engines, and such), but their power is most fully exposed when available as part of a programming language. Examples include Java and JScript, Visual Basic and VBScript, JavaScript and ECMAScript, C, C++, C#, elisp, Perl, Python, Tcl, Ruby, PHP, sed, and awk. In fact, regular expressions are the very heart of many programs written in some of these languages. Ther e's a good reason that regular expressions are found in so many diverse languages and applications: they are extr emely power ful. At a low level, a regular expr ession describes a chunk of text. You might use it to verify a user's input, or perhaps to sift through large amounts of data. On a higher level, regular expressions allow you to master your data. Control it. Put it to work for you. To master regular expressions is to master your data.