Strange Perl pattern matching

[Julien ÉLIE]

Hi Matija,

> On Sat, Jul 04, 2009 at 11:33:26AM +0200, Julien ÉLIE wrote:
>> And the following is fine:
>>
>>    next if ($ngname !~ /$newsgrouppats/);
>>    print "A\n";
>>    next if ($exclusionpats and $ngname =~ /$exclusionpats/);
>>    print "B\n";
>>    next if ($droppats and $ngname =~ /$droppats/);
>>    print "C\n";
>
> perlop(1) for m/PATTERN/msixpogc says:
>
> "If the PATTERN evaluates to the empty string, the last successfully matched
> regular expression is used instead. In this case, only the "g" and "c" flags
> on the empty pattern is honoured - the other flags are taken from the
> original pattern. If no match has previously succeeded, this will (silently)
> act instead as a genuine empty pattern (which will always match)."
>
> so that is probably the problem.


Oh, yes, thanks for having pointed me that feature!
As the third condition is executed only if the regexp for $newsgrouppats *matches*
and the one for $exclusionpats does not match, it always matches when there is the
first condition.

I see that Perl6 will change that behaviour:  an empty pattern will always match.
    http://dev.perl.org/perl6/rfc/144.html

-- 
Julien ÉLIE

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