my $bin = sprintf "%b", hex $hex;

##</code><code>##

sub bin2dec 
{ 
   my @bits = reverse split '', shift; 
   my $num = 0; 
   for( my $i=0; $#bits >= $i; ++$i )
   { 
      $num += 2 ** $i if $bits[$i] 
   } 
   return $num 
}

my $hex = sprintf "%x", bin2dec( $bin )