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

[download]

In reply to Re^2: Parenthesis grouping into regexes. by BillKSmith
in thread Parenthesis grouping into regexes. by aramisf

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