This little script pulls a list of IPs from the homepage of a Yahoo! product manager, and creates a list of CIDR ranges that cover the mailserver IPs provided

yahoo_cidr.pl

#!/usr/bin/perl
use strict;
use Net::CIDR::Lite;

# pull the IPs from the following
my @lines = `wget -O- http://public.yahoo.com/~vineet/ip.txt 2>/dev/null`;

# Remove the newline from each row
chomp for @lines;

# Extract just the lines that look like a dotted-quad IP address
my @ips = grep { /^\d+\.\d+\.\d+\.\d+$/ } @lines;

# Instantiate a CIDR object
# http://search.cpan.org/~dougw/Net-CIDR-Lite-0.21/Lite.pm
my $cidr = Net::CIDR::Lite->new;

for my $ip ( @ips ){
        # Change the IP into the /24 version
        if( $ip =~ /^(\d+\.\d+\.\d+)\.\d+/ ){
                # Match the first three octets, append a ".0/24"
                my $c = $1 . ".0/24";
                $cidr->add( $c );
        }
}

$cidr->clean();

print join( "\n", $cidr->list() ), "\n";