Adobe FLEX 2-PROGRAMMING ACTIONSCRIPT 3.0 Manual page 298

A special type of noncapturing group is the lookahead group, of which there are two types: the
positive lookahead group and the negative lookahead group.
Use and to define a positive lookahead group, which specifies that the subpattern in the
(?= )
group must match at the position. However, the portion of the string that matches the
positive lookahead group can match remaining patterns in the regular expression. For
example, because
(?=e)
that it matches can be matched by a subsequent part of the regular expression—in this case,
the capturing group,
var pattern:RegExp = /sh(?=e)(\w*)/i;
var str:String = "Shelly sells seashells by the seashore";
trace(pattern.exec(str));
// Shelly,elly
Use and to define a negative lookahead group that specifies that the subpattern in the
(?! )
group must not match at the position. For example:
var pattern:RegExp = /sh(?!e)(\w*)/i;
var str:String = "She sells seashells by the seashore";
trace(pattern.exec(str));
// shore,ore
Using named groups
A named group is a type of group in a regular expression that is given a named identifier. Use
and to define the named group. For example, the following regular expression
(?P<name> )
includes a named group with the identifier named
var pattern = /[a-z]+(?P<digits>\d+)[a-z]+/;
When you use the
exec()
array:
result
var myPattern:RegExp = /([a-z]+)(?P<digits>\d+)[a-z]+/;
var str:String = "a123bcd";
var result:Array = myPattern.exec(str);
trace(result.digits); // 123
Here is another example, which uses two named groups, with the identifiers
var emailPattern:RegExp =
/(?P<name>(\w|[_.\-])+)@(?P<dom>((\w|-)+))+\.\w{2,4}+/;
var address:String = "bob@example.com";
var result:Array = emailPattern.exec(address);
trace(result.name); // bob
trace(result.dom); // example
Named groups are not part of the ECMAScript language specification. They are an
added feature in ActionScript 3.0.
298 Using Regular Expressions
is a positive lookahead group in the following code, the character
:
\w*)
method, a matching named group is added as a property of the
:
digits
e
and :
name dom