ActionScript 3.0 Cookbook

Chapter 13. Regular Expressions

Introduction

One of the most powerful features added to ActionScript 3.0 is regular expressions (more commonly known as regexes or regexps). Regular expressions are, put simply, patterns that can be matched against strings. You may be familiar with other types of patterns, such as wildcards (e.g., * and ?), which can be used to match patterns while searching for files. Patterns are also used in Recipe 9.5. Regular expressions support this type of pattern matching, but they are also much more sophisticated.

Regular expressions can be useful in many situations. For instance, the patterns can be applied against strings to perform a variety of tasks, including:

• Finding substrings beginning with a vowel (a, e, i, o, or u)

• Extracting specific values within a string, such as the year value from a full date

• Validating user input to ensure an email address is formatted correctly

• Stripping out HTML tags from a block of text to remove the markup

The patterns used for regular expressions are built by combining characters that have special meaning and can range from being very simple:

[a-zA-Z]

to being extremely complex and cryptic, such as this regex for matching a valid IP address:

^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])$

Simple patterns, such as .*, are easy to understand, but more complex patterns are difficult to learn and are even harder to implement. Thankfully, every ...