use strict;
use warnings;

use constant {UP    => 0x0<<3, 
              DOWN  => 0x1<<3, 
              LEFT  => 0x3<<3, 
              RIGHT => 0x2<<3, 
              MASK  => 0x3<<3};


printf "direction Mask: ";
print8bits (MASK);  #Prints: direction Mask: 0001 1000 

my $register8b=0;

#set direction left
$register8b = $register8b & ~MASK | LEFT;
print8bits ($register8b); #Prints: 0001 1000 

#set direction down
$register8b = $register8b & ~MASK | DOWN;
print8bits ($register8b);  #Prints: 0000 1000 


sub print8bits
{
   my $int = shift;
  
   print map{s/(\d{4})/$1 /g;$_;}sprintf "%08b\n", $int;
}