Beefy Boxes and Bandwidth Generously Provided by pair Networks
Syntactic Confectionery Delight
 
PerlMonks  

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 (Abbot) 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.

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1022903]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others scrutinizing the Monastery: (18)
As of 2015-07-02 17:52 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









    Results (44 votes), past polls