http://qs321.pair.com?node_id=667555

wolfger has asked for the wisdom of the Perl Monks concerning the following question:

I whipped up a quick regex today to satisfy a range of possible domain names, and while it matches everything I want, it also matches a few things I don't want. Easy enough to error-proof with an "if", but I'm wondering if there's a way to wrap this all up in one regex. Here's what I have:

abc[123]\.xy[z1]1?\.nota\.url

The only problem is in the xyz11? part of the expression. I want to match xyz, xy1, and xyz1, but not xy11, and I couldn't figure out how to limit that.

--
Nothing to see here. Move along.

Replies are listed 'Best First'.
Re: wanting a more explicit regex
by moritz (Cardinal) on Feb 12, 2008 at 13:47 UTC
    You can use an alternation: xy(?:z|1|z1)

    If the list of possible alternations grows too large to list them explicitly, you have to tell us a bit more about your problem, perhaps there's a better, generic solution.

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Re: wanting a more explicit regex
by poolpi (Hermit) on Feb 12, 2008 at 14:12 UTC 
    #!/usr/bin/perl
use strict;
use warnings;

my @url = ( 'a2.xyz', 'c3.xy1', 'b1.xyz1', 'a3.xy11');

for (@url){
   $_ .= '.nota.url';

    / [a-c][1-3]
      [.]
      xy (:? z[1]? | 1 )
      [.]
      nota
      [.]
      url
    /xms ? print "$_ : OK\n" : print "$_ : NOK\n";
}

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    Output:
a2.xyz.nota.url : OK
c3.xy1.nota.url : OK
b1.xyz1.nota.url : OK
a3.xy11.nota.url : NOK

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    hth,
    PooLpi

    'Ebry haffa hoe hab im tik a bush'. Jamaican proverb
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Re: wanting a more explicit regex
by Anonymous Monk on Feb 12, 2008 at 14:21 UTC 
    use Regex::PreSuf;
my $re = presuf(qw( abc1 abc2 abc3 xyz1 xyz xy1 nota url ));
print "$re\n";
__END__
(?:abc[123]|nota|url|xy(?:z1|[1z]))

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