in reply to Re^2: Seeker of Regex Wisdom (strings which don't form specific patterns)
in thread Seeker of Regex Wisdom (strings which don't form specific patterns)

Hi Discipulus,

your suggestion is a pure regex, which makes perfect sense in J. Friedl's book, but I do not think it is more selective than my proposal, mixing a regex and some arithmetics, which looks for four dot-separated integer numbers smaller than 256. (Except that I used \d instead of [0-9] for brevity, so that my regex might match (non-Arabic) Unicode digits, but that's easily fixed.)

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Re^4: Seeker of Regex Wisdom (strings which don't form specific patterns)
by AnomalousMonk (Archbishop) on Aug 13, 2015 at 10:04 UTC
    perl -ne 'print if /(\d{1,3}\.){3}(\d{1,3})/ and $1 < 256 and ... and $4 < 256;'

    Unfortunately, capture groups don't change their numbering under a counted quantifier (a misapprehension I've suffered more than once), so it's necessary to use four explicit captures for the above to work: 

    c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"$_ = '12.34.56.78';
 ;;
 /(\d{1,3}\.){3}(\d{1,3})/;
 dd [ $1, $2, $3, $4 ];
 ;;
 /(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})/;
 dd [ $1, $2, $3, $4 ];
"
["56.", 78, undef, undef]

[12, 34, 56, 78]

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      Unfortunately, capture groups don't change their numbering under a counted quantifier

      One way to overcome that is keeping track oneself: 

      $_ = '192.168.2.111';
my @l;
/^(?:([01]?\d\d?|2[0-4]\d|25[0-5])(?{push@l,$1})\.){3}([01]?\d\d?|2[0-
+4]\d|25[0-5])$/;
print join('-',@l,$2),"\n";
__END__
192-168-2-111

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      perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'
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In Section Seekers of Perl Wisdom