use strict;
use warnings;

use constant  {
  START_IP_BYTE4 =>   2,
  MAX_IP_BYTE4   => 254,
  SLEEP          =>  12 * 3600
};

my @ip = qw(192 168 10 2);
$ip[3] = shift || START_IP_BYTE4;


while ( 'true' ) {
  set_ip( @ip );
  $ip[3]++;
  $ip[3] = START_IP_BYTE4 if $ip[3] > MAX_IP_BYTE4;

  print "Next change: " . localtime( time() + SLEEP ) . "\n";
  sleep SLEEP; # floating!
}
die "oops! $! / $@";

sub set_ip {
  my @ip = @_;
  my $ip = join( '.', @ip );
  print "Setting local IP to $ip...\n";
  print "Load file 'ip$ip[3].txt' ???\n";
  #TODO: set local IP
}