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
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
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.
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
colour, but not
Console.WriteLine (Regex.Match ("color", @"
colou?r").Success); // ...