Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!texsun!letni!mic!convex!convex.COM
From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: Matching parentheses
Message-ID: <109450@convex.convex.com>
Date: 29 Nov 90 00:18:12 GMT
References: <1990Nov28.150131.28981@ugle.unit.no>
Sender: news@convex.com
Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
Lines: 16

In article <1990Nov28.150131.28981@ugle.unit.no> harald.alvestrand@elab-runit.sintef.no writes:
>I have thought a long time about this, but I am sure there must be some
>magic way to do it:
>How can I write a pattern that matches (), ((())), ((())()), but NOT ((())?
>That is, how do I get a balanced matching of parentheses?
>(or quotes, for that matter...)

No, there's no "magic" way of doing it.  The problem is that regular
expressions are really nice, but they just can't handle recursive
structures -- at least, not by themselves.  To deal with these in Perl,
you could interatively process /\(([^\)]*)\)/ to deal with things from the
inside-out.  Simple approaches like that one won't work well with escaped
characters; you'll need to change them into something else (like \201)
before the search, or else you'll match where you don't want to.

--tom