XOR swapping of strings in perl is BAD. I think it's merlyn who refers to these things as bad memes?

The reason is that if the strings are different lengths, you get subtly "broken" results...

my ($a,$b)=("a","bb"); 
printf("/%s/ (%d bytes) /%s/ (%d bytes)\n",$a,length($a),$b,length($b)
+);
$a^=$b^=$a^=$b;
printf("/%s/ (%d bytes) /%s/ (%d bytes)\n",$a,length($a),$b,length($b)
+);'
[download]

This results in:

/a/ (1 bytes) /bb/ (2 bytes)
/bb/ (2 bytes) /a/ (2 bytes)
[download]

The unexpected "2 bytes" for /a/ occurs because the string is still 2 characters long, but the 2nd character is now null.

This can (and will) trip you up later, because $b ne "a", even though they print the same.
--
Mike