Excuse me for my badly formatted reply.
I've missed to RTF.How To display...:>

Here the piece of code I suggest:

my $length;

open( FILE1, "string1" );
open( FILE2, "string2" );

$string1 = <FILE1>;
$string2 = <FILE2>;

map {
	$a = substr($string1, $_, 1);
	$b = substr($string2, $_, 1);
	print "$b$a ";
} reverse(0 .. length($string1) - 1);