Regular expression syntax

This section describes all of the elements of ActionScript regular expression syntax. As you’ll see, regular expressions can have many complexities and nuances. You can find detailed resources on regular expressions on the web and in bookstores. Keep in mind that different programming environments implement regular expressions in different ways. ActionScript 3.0 implements regular expressions as defined in the ECMAScript edition 3 language specification (ECMA-262).

Generally, you use regular expressions that match more complicated patterns than a simple string of characters. For example, the following regular expression defines the pattern consisting of the letters A, B, and C in sequence followed by any digit:

/ABC\d/

The \d code represents “any digit.” The backslash (\) character is called the escape character, and combined with the character that follows it (in this case the letter d), it has special meaning in the regular expression. This chapter describes these escape character sequences and other regular expression syntax features.

The following regular expression defines the pattern of the letters ABC followed by any number of digits (note the asterisk):

/ABC\d*/

The asterisk character (*) is a metacharacter. A metacharacter is a character that has special meaning in regular expressions. The asterisk is a specific type of metacharacter called a quantifier, which is used to quantify the amount of repetition of a character or group of characters. For more information, see Quantifiers.

In addition to its pattern, a regular expression can contain flags, which specify how the regular expression is to be matched. For example, the following regular expression uses the i flag, which specifies that the regular expression ignores case sensitivity in matching strings:

/ABC\d*/i

For more information, see Flags and properties.

You can use regular expressions with the following methods of the String class: match(), replace(), and search(). For more information on these methods, see Finding patterns in strings and replacing substrings.