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;
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