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Regular Expressions

found, a reluctant quantifier continues to add characters from the string until either a match is found or

the entire string is checked without a match. Reluctant quantifiers work in reverse of greedy quantifiers.

Possessive quantifier

only tries to match against the entire string. If the entire string doesn’t produce a

match, no further attempt is made. Possessive quantifiers are, in a manner of speaking, a one-shot deal.

What makes a quantifier greedy, reluctant, or possessive? It’s really all in the use of the asterisk, question

mark, and plus symbols. For example, the question mark alone (

) is greedy, but a question mark fol-

lowed by another question mark (

) is reluctant. To make the question mark possessive, append a plus

sign (

). The following table shows all the greedy, reluctant, and possessive versions of the quantifiers

you’ve already learned.

Greedy Reluctant

Possessive

Description

Zero or one occurrences

Zero or more occurrences

One or more occurrences

{

}

{

Exactly

occurrences

{

}

{

At least

but no more than

occurrences

{

,}?

{

,}+

At least

occurrences

To illustrate the differences among the three kinds of quantifiers, consider the following example:

var sToMatch =”abbbaabbbaaabbb1234”;

var re1 = /.*bbb/g; //greedy

var re2 = /.*?bbb/g; //reluctant

var re3 = /.*+bbb/g; //possessive

You want to match any number of letters followed by

bbb

. Ultimately, you’d like to get back as matches

“abbb”

“aabbb”

, and

“aaabbb”

. However, only one of the three regular expressions returns this result,

can you guess which one?

If you guessed

re2

, congratulations! You now understand the difference between greedy, reluctant, and

possessive quantifiers. The first regular expression,

re1

, is greedy and so it starts by looking at the

whole string. Behind the scenes, this is what happens:

re1.test(“abbbaabbbaaabbb1234”); //false - no match

re1.test(“abbbaabbbaaabbb123”); //false - no match

re1.test(“abbbaabbbaaabbb12”); //false - no match

re1.test(“abbbaabbbaaabbb1”); //false - no match

re1.test(“abbbaabbbaaabbb”); //true – match!

So the only result that

re1

returns is

“abbbaabbbaaabbb”

. Remember, the dot represents any character,

and

is included, therefore

“abbbaabbbaaa”

matches the

part of the expression and

“bbb”

matches

the

bbb

part.

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Regular Expressions

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