Re^2: Parenthesis grouping into regexes.

[BillKSmith]

Here is an example with data made up to match your regular expressions. Are you sure about the fourth colon in $ip6?

use strict;
use warnings;
my $ip4     = qr !(?: [0-9]{1,3}\.){3} [0-9]{1,3} !x;
my $ip6     = qr !(?: [a-f0-9]{4}:)+ !x;
my $prefix  = qr ! / \d \d !x;
my $pattern = qr ! ^($ip4|$ip6) ($prefix)? !x;

while (<DATA>) {
    next if  $_ !~ $pattern;
    print "Hey, I found \$1: $1 \$2: $2\n";
}
__DATA__
no match here
999.888.777.666/66
aaaa:aaaa:aaaa:aaaa:/77

[aramisf]

Labelling groups (with (?pattern) regex) showed me what was happening. It is all clear now.

Many thanks to everyone, specially BillKSmith!

I was having a trouble when using $1, $2... because I didn't know they exact behaviour.

The problem I had was with the parenthesis inside $ip4 regex, causing $2 to have an ip address,
$3 had the match inside the parenthesis in $ip4, and the prefix I expected put into $4:

# Example of my debug output:

line = '*> 177.101.16.0/21  200.19.74.230   0    200'
matches: $1:'*> ' $2:'177.101.16.0' $3: '16.' $4:'/21'

Now I understand how $1, $2, $3... are set.
Thank you all, Monks! =D