Hi!

#!/usr/bin/perl
# vim: sw=4

use strict;
use warnings;

my ($vlan, $ipaddress, $netmask);
my %interfaces; # great variable name.
while (<DATA>) {
    if (/^interface Vlan(\d+)/) {
        $vlan = $1;
    }
    elsif (/no ip address/) {
        ($vlan, $ipaddress, $netmask) = (undef, undef, undef);
        next;
    } 
    elsif (/ip address ((\d+\.){3}\d+) ((\d+\.){3}\d)/) {
        ($ipaddress, $netmask) = ($1, $3);
    }
    elsif (/^!$/ && $ipaddress && $netmask) {
        $interfaces{$vlan}->{ip} = $ipaddress;
        $interfaces{$vlan}->{netmask} = $netmask;
    }
}

use Data::Dumper;
print Dumper \%interfaces;

__DATA__
interface Vlan1
 no ip address
 no ip route-cache
 shutdown
!
interface Vlan12
 ip address 68.142.192.79 255.255.255.0
 no ip route-cache
 shutdown
!
interface Vlan8
 ip address 68.142.192.79 255.255.255.0
 no ip route-cache
!
[download]

The output of this code is-

$VAR1 = {
          '8' => {
                   'ip' => '68.142.192.79',
                   'netmask' => '255.255.255.0'
                 },
          '12' => {
                    'ip' => '68.142.192.79',
                    'netmask' => '255.255.255.0'
                  }
        };
[download]