Re: trouble with question mark in regex

On Thu, 2 Apr 2009 15:47:11 +0200
Thomas Michael Hagen <[email protected]> wrote:

> the usual behavior for ? is to make sure you capture the shortest
> match. this does not seem to work in gerh.
> 
> this is my code:
> 
> match (:: :intro: :not-used: :text-chunk: :beginning-of-next-article:)
> [:ffile:] /(#http:.*?(CET|CEST) ....)(.*?)(#http:|$)/
> 
> i am searching through a file that contains newspaper articles
> beginning with a header that looks something like this:
> 
> #http://fotball.bt.no/eliteserien/article131749.ece
> Wed Mar 11 19:08:07 CEST 2009
> 
> i want to capture these first two lines with the variable :intro:,
> however, at the very end of each article (in some newspapers), there
> is a field where the journalists put their name and a timestamp. it
> looks like this:
> 
> S: trond
> T: Mon Sep 25 18:14:15 CEST 2006
> 
> the problem is that my program completely ignores the first timestamp,
> and puts the entire article into the :intro: variable.


I did some experimentation awhile back with right associative matching
and I found that "(?r:expression)" was useless for my purposes - not
because there is no use case for right associative matching, but
because the regex library could not be relied on to default to left
associative behavior in expressionions like /begin(.*?)marker(.*?)end/
where "marker" occurs more than once between "begin" and "end". This
looks like a TRE regex bug. I have no idea whether it's documented.

In this case, you are trying to obtain left associative behovior and it
just isn't happening for you. For work arounds, you can break out your
submatch into a separate match statement or build an expression that
includes the second time stamp explicitly. The latter approach will be
marginally faster, but its feasibility can only be determined with your
domain-specific knowledge. 

Chris

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