use strict;
use warnings;

use feature qw{ say };

use Socket;

my $ipAddr = shift;
my( $quad, $mask ) = split m{/}, $ipAddr;

die qq{Bad IP\n} unless my $binAddr = inet_aton( $quad );

my $rxValidMask = do {
   local $" = q{|};
   my @vals = ( 8 .. 30 );
   qr{^(?:@vals)$};
   };
die qq{Bad mask\n} unless $mask =~ $rxValidMask;

my $value   = 0xffffffff;
$value      = do {
   no warnings qw{ portable };
   ( $value <<= 1 ) % 0x100000000;
   } for 1 .. ( 32 - $mask );
my $binMask = pack q{N}, $value;

my $network = $binAddr & $binMask;

my $lowMask = $network ^ pack q{H*}, q{00000001};
my $lowAddr = $network | $lowMask;

my $highMask = $binMask ^ pack q{H*}, q{ffffffff};
my $highAddr = $network | $highMask;

my $hrNetwork
   = inet_ntoa( $network )
   . q{/}
   . ( unpack( q{B*}, $binMask ) =~ tr{1}{} );

print qq{\n};
my $lineFmt = qq{%-13s: %s %s %s %s : %s\n};
printf
   $lineFmt x 5,
   q{IP address},
      unpack( q{(a8)*}, unpack( q{B*}, $binAddr ) ), $quad,
   q{Netmask},
      unpack( q{(a8)*}, unpack( q{B*}, $binMask ) ), inet_ntoa( $binMask ),
   q{Network},
      unpack( q{(a8)*}, unpack( q{B*}, $network ) ), $hrNetwork,
   q{Low address},
      unpack( q{(a8)*}, unpack( q{B*}, $lowAddr ) ), inet_ntoa( $lowAddr ),
   q{High address},
      unpack( q{(a8)*}, unpack( q{B*}, $highAddr ) ), inet_ntoa( $highAddr );

print qq{\nAddress range\n};
do {
   say q{     }, inet_ntoa( $lowAddr );
   $lowAddr = pack q{N}, 1 + ( unpack q{N}, $lowAddr );
   } while $lowAddr le $highAddr;

##</code><code>##

johngg@shiraz:~/perl/Monks > ./spw1174132 1.2.3.4/27

IP address   : 00000001 00000010 00000011 00000100 : 1.2.3.4
Netmask      : 11111111 11111111 11111111 11100000 : 255.255.255.224
Network      : 00000001 00000010 00000011 00000000 : 1.2.3.0/27
Low address  : 00000001 00000010 00000011 00000001 : 1.2.3.1
High address : 00000001 00000010 00000011 00011111 : 1.2.3.31

Address range
     1.2.3.1
     1.2.3.2
     1.2.3.3
     1.2.3.4
     1.2.3.5
     1.2.3.6
     1.2.3.7
     1.2.3.8
     1.2.3.9
     1.2.3.10
     1.2.3.11
     1.2.3.12
     1.2.3.13
     1.2.3.14
     1.2.3.15
     1.2.3.16
     1.2.3.17
     1.2.3.18
     1.2.3.19
     1.2.3.20
     1.2.3.21
     1.2.3.22
     1.2.3.23
     1.2.3.24
     1.2.3.25
     1.2.3.26
     1.2.3.27
     1.2.3.28
     1.2.3.29
     1.2.3.30
     1.2.3.31

##</code><code>##

johngg@shiraz:~/perl/Monks > ./spw1174132 1.2.3.4/18

IP address   : 00000001 00000010 00000011 00000100 : 1.2.3.4
Netmask      : 11111111 11111111 11000000 00000000 : 255.255.192.0
Network      : 00000001 00000010 00000000 00000000 : 1.2.0.0/18
Low address  : 00000001 00000010 00000000 00000001 : 1.2.0.1
High address : 00000001 00000010 00111111 11111111 : 1.2.63.255

Address range
     1.2.0.1
     1.2.0.2
     1.2.0.3
     1.2.0.4
     1.2.0.5
     1.2.0.6
     1.2.0.7
     1.2.0.8
     1.2.0.9
     1.2.0.10
     1.2.0.11
     1.2.0.12
     1.2.0.13
     1.2.0.14
     1.2.0.15
     1.2.0.16
     1.2.0.17
...
     1.2.63.241
     1.2.63.242
     1.2.63.243
     1.2.63.244
     1.2.63.245
     1.2.63.246
     1.2.63.247
     1.2.63.248
     1.2.63.249
     1.2.63.250
     1.2.63.251
     1.2.63.252
     1.2.63.253
     1.2.63.254
     1.2.63.255