C# 3.0 in a Nutshell, 3rd Edition

Chapter 24. Regular Expressions

The regular expressions language identifies character patterns. The .NET types supporting regular expressions are based on Perl 5 regular expressions and support both search and search/replace functionality.

Regular expressions are used for tasks such as:

• Validating text input such as passwords and phone numbers (ASP.NET provides the RegularExpressionValidator control just for this purpose)

• Parsing textual data into more structured forms (e.g., extracting data from an HTML page for storage in a database)

• Replacing patterns of text in a document (e.g., whole words only)

This chapter is split into both conceptual sections teaching the basics of regular expressions in .NET and reference sections describing the regular expressions language.

All regular expression types are defined in System.Text.RegularExpressions.

Tip

For more on regular expressions, http://regular-expressions.info is a good online reference with lots of examples, and Mastering Regular Expressions by Jeffrey E. F. Friedl (O’Reilly), is invaluable for the serious.

Regular Expression Basics

One of the most common regular expression operators is a quantifier. ? is a quantifier that matches the preceding item 0 or 1 time. In other words, ? means optional. An item is either a single character or a complex structure of characters in square brackets. For example, the regular expression "colou?r" matches color and colour, but not colouur:

Console.WriteLine (Regex.Match ("color",   @"colou?r").Success); // ...