$temp = $a;
$a = $b;
$b = $a;

##</code><code>##

$a ^= $b;
$b ^= $a;
$a ^= $b;

##</code><code>##

$a .= $b;
$b = substr($a,0,length($a)-length($b));
substr($a,0,length($b)) = '';

##</code><code>##

$a += $b;
$b = $a - $b;
$a -= $b;

##</code><code>##

$a ^= $b;
$b ^= $a;
$a ^= $b;