# wrong beaviour as it doubles the memory
# first code of my previous post, very similar to the OP one
my $x = 'a' x (2**30); 


# RIGHT beaviour, it does NOT double memory used
# second code posted above 
my $x; 
foreach my $order ( qw(20 24 30 32) ){
    $x = 'a' x ( 2 ** $order );
    ...

# RIGHT beaviour, even with my $x declared inside the foreach loop
foreach my $order ( qw(20 24 30 32) ){
	my $x = 'a' x ( 2 ** $order );
        ...