my $long_string = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

my $i          = 0;
my $readlength = 8;

# non destructive
while ( $i <= length($long_string) ) 
{
	my $part = substr( $long_string, $i, $readlength );
	$i += $readlength;
	
	print "$part\n";
}


# destructive
while ( $long_string =~ s/^(.{1,$readlength})// ) 
{
	my $part = $1;
	print "$part\n";
}