Octet Regex

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

In my endless search for the perfect regex, I have encountered this problem over and over again.

### Haxor ###
#!/usr/bin/perl -w

use strict;
use warnings;

my $flag = 0;
my $hacklist = "hack.txt";
my $date = 'Date:    ';
my $octet = '(\d{1,3}\.){3}\d{1,3}';

open HACK, $hacklist or die "Can't Open $hacklist";
my @hack=<HACK>;
close(HACK);

foreach (@hack) {
    
    if (s/$date//){
        print;
        $flag = 0;
    }    
    if (/$octet/ and !$flag){
        print STDOUT $_;
        print "\n";
        $flag = 1;
        }
    }
[download]

Simple, parse the dates and octets from the hacklist. Currently I get this:

Thursday, December 13, 2001  07:53 AM
Subject:        FW: Please disconnect 208.202.183.42 thanks.

Monday, December 17, 2001  08:56 AM
Subject:        FW: Please disconnect 213.14.199.133 thanks.
[download]

But how do I print only the octet? Everything else on that line is unecessary. Is there a way to print only the matched pattern, disregarding everything else on the line? Ideal results would be:

Thursday, December 13, 2001  07:53 AM
208.202.183.42

Monday, December 17, 2001  08:56 AM
213.14.199.133
[download]

Hopefully I will get 'Mastering Regular Expressions' for Christmas. Happy Holidays!

Comment on Octet Regex Select or Download Code

Replies are listed 'Best First'.
Re: Octet Regex by joealba (Hermit) on Dec 18, 2001 at 00:32 UTC
Use a backreference. `if (!$flag && /($octet)/){ print "$1\n"; }` [download] From Camel 3, p. 41: A pair of parenthesis around a part of a regular expression causes whatever was matched by that part to be remembered for later use. `$1` is the match from the first set of parenthesis in your regexp, `$2` the second, and so on.	[reply] [d/l] [select]
Re: Octet Regex by count0 (Friar) on Dec 18, 2001 at 00:44 UTC
You should also use the 'qr' operator in this case for quoting your regexp (see perlop, and perlre). `my $octet = qr!(\d{1,3}\.){3}\d{1,3}!;`	[reply] [d/l]