From: "Stephan Kämper" <Stephan.Kaemper@...>
Date: 2002-02-27T00:25:39+09:00
Subject: Re: Nested paired brackets in regexp

Yasuo Saito wrote:
> 
> Hi.
> 
> Ruby's regular expression is very powerful.
> 
> But, I cannot express paired brackets(<...>), which
> might be nested, in a single regular expression.
> 
> How can I check nested paired brackets by a single/simple
> (extended) regular expression, if possible?
> 
> eg.
>  input            | expected
> ------------------+--------------
> "ab<cd>ef"        | "<cd>"
> "ab<cd>e<fg>"     | "<cd>"
> "ab<cd<e<>fg>h>i" | "<cd<e<>gh>i>"
> "ab<cd<e>f"       | not matched
> 
> Y.Saito

If I remember corretly what I've read in Friedl's "Mastering Regular
Expressions" (O'Reilly),
there's a principal reason why matching nested pairs of brackets (or
whatever can be paired)
isn't possible.

Note that there _are_ ways to match paired braces up to a certain nesting
level (if you like
I can check in my copy of Friedl's book, I just don't have it at hand right
now...).

Hope that helps


Stephan