use Data::Dumper; 

%x =
  ( 1 => 2,
    3 => $x{1}
  );


print Dumper(\%x), $/;

$y{1} = 2;
$y{2} = $y{1};

print Dumper(\%y), $/;


##</code><code>##

cctbrann@mcynote ~/tests : perl fastbind.pl
$VAR1 = {
          '1' => 2,
          '3' => undef
        };

$VAR1 = {
          '1' => 2,
          '2' => 2
        };