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Re^2: Using variable to hold regex expression

by salatconed (Initiate)
on Mar 12, 2013 at 00:05 UTC ( #1022903=note: print w/ replies, xml ) Need Help??


in reply to Re: Using variable to hold regex expression
in thread Using variable to hold regex expression

Perhaps using IP addresses was not a good example, I'm trying to figure out how to parse a string which has repetitive data, so I can write the regex expression once and get multiple returns if they exist the same way your code got both IP addresses in one call.


Comment on Re^2: Using variable to hold regex expression
Re^3: Using variable to hold regex expression
by Kenosis (Priest) on Mar 12, 2013 at 00:31 UTC

    If I'm understaing you correctly, the my ( $firstIP, $secondIP ) = /($RE{net}{IPv4})/g in the above code does what you've described.

Re^3: Using variable to hold regex expression
by AnomalousMonk (Monsignor) on Mar 12, 2013 at 00:35 UTC
    ... how to parse a string which has repetitive data ...

    As choroba pointed out, every  (pattern) pair of parentheses in a regex captures something (even undef possibly) to its corresponding capture variable. One way to parse a string using nested regexes is avoid using a gazillion capturing groups. Use the non-capturing  (?:pattern) instead for grouping. See perlre, perlrequick, perlretut. In the IP example (but this should generalize to any repetitive data you wish to extract):

    >perl -wMstrict -le "my $decimal_octet = qr{ 2 (?: [0-4] \d | 5 [0-5]) | [01]? \d? \d }xms; my $ip = qr{ (?<! \d) $decimal_octet (?: \. $decimal_octet){3} (?! \d) }xms; print $ip; ;; my $s = '123.45.6.234 xx yyy zz 000.12.34.255'; my @ips = $s =~ m{ $ip }xmsg; printf qq{'$_' } for @ips; " (?^msx: (?<! \d) (?^msx: 2 (?: [0-4] \d | 5 [0-5]) | [01]? \d? \d ) (? +: \. (?^msx: 2 (?: [0-4] \d | 5 [0-5]) | [01]? \d? \d )){3} (?! \d) ) '123.45.6.234' '000.12.34.255'

    Note that neither  (?:pattern) nor the  (?<!pattern) (?!pattern) look-around assertions capture. Indeed, nothing captures (to a capture variable) since data is extracted in list context directly to an array.

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