Beefy Boxes and Bandwidth Generously Provided by pair Networks
XP is just a number
 
PerlMonks  

Re^3: Using variable to hold regex expression

by AnomalousMonk (Monsignor)
on Mar 12, 2013 at 00:35 UTC ( #1022906=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Using variable to hold regex expression
in thread Using variable to hold regex expression

... 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.


Comment on Re^3: Using variable to hold regex expression
Select or Download Code

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1022906]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others having an uproarious good time at the Monastery: (8)
As of 2014-08-01 00:19 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    My favorite superfluous repetitious redundant duplicative phrase is:









    Results (256 votes), past polls