#!/usr/bin/perl
use strict;
use warnings;
use Socket;

my $ifconfig='/usr/sbin/ifconfig';

# run ifconfig -a
open my $if, '-|', "$ifconfig -a" or die "Couldn't run $ifconfig: $!\n";
while (<$if>) {
        # find a line with "broadcast" in it
        # on Solaris this contains all the information I need
        next unless /inet\s+(.*?)\s+netmask\s+(.*?)\s+broadcast\s+(.*?)\s*$/;

        # keep ip address as it is (a dotted string)
        my $iaddr= $1;

        # convert the netmask to a "long"
        my $netmsk= hex "0x$2";

        # dito for the broadcast
        my $brdcst= unpack 'N', inet_aton $3;

        # How many bits does the netmask have?
        my $bits= 31-int(log(0xffffffff ^ $netmsk)/log(2));

        # Convert the netmask to a "slashed" IP
        my $network= inet_ntoa(pack "N", ($brdcst & $netmsk)) . "/" . $bits;

        # show all info found
        print "$iaddr\t$network\n";
}
close $if;