From: "David A. Black" <dblack@...>
Date: 2005-08-25T00:57:47+09:00
Subject: Re: Novice Q: What's the difference between /\s*/ and /(\s)*/?

Hi --

On Thu, 25 Aug 2005, Jeff Wood wrote:

> Ok, now for a clean and simple answer...
>
> The parenthesis create "groups".  Groups give you the ability to save
> away parts of the matched pattern for easy access after a match has
> been made. And yes, the O'Reilly book "Mastering Regular Expressions"
> would be a good read it explains this concept quite completely.
>
> When you use Regexp#match, if you find a match, you are returned a
> MatchData object which provides an [] API for standard array style
> access.
>
> Element 0 ( [0] ) provides the COMPLETE match. If you defined any
> groups in the regular expression, they will then appear as additional
> elements in the MatchData [] array. Each group is then accessable
> using ordinals ( [1] .. [9] I don't know what happens after 9, I've
> never needed that many ) ...

I believe that would be 10 :-)

   irb(main):003:0> m = /(((((((((((a)))))))))))/.match("a")
   => #<MatchData:0xbf4bbd84>
   irb(main):004:0> $10
   => "a"
   irb(main):005:0> m[10]
   => "a"


> Remember that if you define a group to be
> inside an optional region of the regular expression, that group will
> return nil.

I'm not sure what you mean there.

   irb(main):009:0> /((a)?)?/.match("a").to_a
   => ["a", "a", "a"]


David

-- 
David A. Black
dblack@wobblini.net