ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Using regular expressions
Important concepts and terms
The following reference list contains important terms that are relevant to this feature:
Escape character A character indicating that the character that follows should be treated as a metacharacter rather
than a literal character. In regular expression syntax, the backslash character (\) is the escape character, so a backslash
followed by another character is a special code rather than just the character itself.
Flag A character that specifies some option about how the regular expression pattern should be used, such as whether
to distinguish between uppercase and lowercase characters.
Metacharacter A character that has special meaning in a regular expression pattern, as opposed to literally
representing that character in the pattern.
Quantifier A character (or several characters) indicating how many times a part of the pattern should repeat. For
example, a quantifier would be used to designate that a United States postal code should contain five or nine numbers.
Regular expression A program statement defining a pattern of characters that can be used to confirm whether other
strings match that pattern or to replace portions of a string.
Regular expression syntax
Flash Player 9 and later, Adobe AIR 1.0 and later
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.
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” on page 82.
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” on page 87.
Last updated 6/6/2012
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