Note that XOR will not work properly in at least three cases: if the variable is a large value, a reference, or is undefined. The other two methods handle all three without a problem. (although -w will complain about the undef). Just something to watch out for.

sub xor { $a = $a ^ $b; $b = $a ^ $b; $a = $a ^ $b; }
@foo= qw(bar none at all);

$a=999999999999;
$b=8888888;
print "BEFORE: A=$a B=$b\n";
&xor();
print "AFTER:  A=$a B=$b\n\n";

$a=\@foo; $b=8888888;
print "BEFORE: A=$a ($a->[0]) B=$b\n";
&xor();
print "AFTER:  A=$a ($a->[0]) B=$b\n\n";

$a=undef; $b=8888888;
print "BEFORE: A=$a B=$b\n";
&xor();
print "AFTER:  A=$a B=$b\n\n";

## Running the above produces:
BEFORE: A=999999999999 B=8888888
AFTER:  A=8888888 B=4294967295

BEFORE: A=ARRAY(0x87650a4) (bar) B=8888888
AFTER:  A=8888888 () B=141971620

BEFORE: A= B=8888888
AFTER:  A=8888888 B=0
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