I wrote something similar to that a few years ago:
#!/usr/bin/perl
use warnings;
use strict;
use Socket;
$0 =~ s|.*/||;
@ARGV == 2 or die "usage: $0 address netmask\n";
my $address = inet_aton( shift );
my $netmask = inet_aton( shift );
my $bits = unpack '%32b*', $netmask;
my $class = vec( $address, 7, 1 ) ? vec( $address, 6, 1 ) ? vec( $addr
+ess, 5, 1 ) ? 'D' : 'C' : 'B' : 'A';
printf "Address: %15s\n", inet_ntoa( $address );
printf "Netmask: %15s\n", inet_ntoa( $netmask );
printf "Network: %15s/%d (Class %s)\n", inet_ntoa( $netmask & $add
+ress ), $bits, $class;
printf "Broadcast: %15s\n", inet_ntoa( ~$netmask | $add
+ress );
printf "HostMin: %15s\n", inet_ntoa( ($netmask & $add
+ress) | "\x00\x00\x00\x01" );
printf "HostMax: %15s\n", inet_ntoa( (~$netmask | $add
+ress) & "\xFF\xFF\xFF\xFE" );
printf "Hosts/Net: %15s\n", 2 ** ( 32 - $bits ) - 2;