From: "Brian Schröder" <ruby@...>
Date: 2004-10-05T18:09:06+09:00
Subject: Re: Regexp match question on interpolated strings...

Richard Kilmer wrote:
> If I had the source for a string:
> 
> "name = #{person.first_name+" "+person.last_name} ... Ok?"
> 
> And assuming I could find the first and last double quotes, how would I
> parse out the #{ ... } with a regular expression since anything can fall
> between the #{ ... } braces in a string?
> 
> Thanks in advance.
> 
> -rich
> 
> 
> 
Regular expressions are not able to "count" more than a finite number of 
states, and the number of states is fixed at compile time. That is 
because regular expressions map to finite automata. So it is impossible 
to match opening and closing braces in an unknown expression. For this 
to work always you need a model that can enter unbounded many states.

But beware, your computer is also only a finite state machine with a lot 
of states. The number of its states is bounded by the size of ram (and 
harddisk).

If you are shure that there will be no closing braces inside of the 
braces you could match
/\#\{(.*?)\}/ =~ string

or including at most one pair of inside braces

/\#\{([^\{}]*(\{.*?\}|).*?)\}/ =~ string

As you see it begins to get ugly now.

Regards,

Brian
-- 
Brian Schr�der
http://ruby.brian-schroeder.de/