$str = "135";
substr($str, 1, 1) = "234";
print $str;
This should give you "12345";

##</code><code>##

$str1 = "01";                                
$str2 = "1";
print "equal as numbers\n" if ($str1 == $str2);
print "equal as strings\n" if ($str1 eq $str2);