From: James Edward Gray II <james@...>
Date: 2005-04-01T06:01:56+09:00
Subject: Re: Regex parsing question

On Mar 31, 2005, at 2:49 PM, Paul Hanchett wrote:

> Why does this:
>
> 	text= "AA<X>BB<X>CC</X>DD</X>EE"
> 	regex = %r{(.*)<X>(.*)}
>
> 	t = text.sub( regex, "z" );
> 	print "$1=#{$1}\n$2=#{$2}\n$3=#{$3}\n$4=#{$4}\n"
>
> Return this:
>
> 	$1=AA<X>BB
> 	$2=CC</X>DD</X>EE
> 	$3=
> 	$4=

Because the construct .* means, "Zero of more non-newline characters, 
but as many as I can get".    We say the * operator is "greedy".

> Instead of:
>
> 	$1=AA
> 	$2=BB<X>CC</X>DD</X>EE
> 	$3=
> 	$4=
>
> And how would I fix it?

One way would be to switch from the greedy * to the conservative *?.  
That would have your Regexp looking like this:

%r{(.*?)<X>(.*)}

Another way is to use split() with a limit:

irb(main):001:0> text= "AA<X>BB<X>CC</X>DD</X>EE"
=> "AA<X>BB<X>CC</X>DD</X>EE"
irb(main):002:0> first, rest = text.split(/<X>/, 2)
=> ["AA", "BB<X>CC</X>DD</X>EE"]
irb(main):003:0> first
=> "AA"
irb(main):004:0> rest
=> "BB<X>CC</X>DD</X>EE"

Hope that helps.

James Edward Gray II