Just a comment on forms for this kind of problem.

The first two forms explicitly list each variable only once: 

my $only_one = 1 == ($x ? 1 : 0) + ($y ? 1 : 0) + ($z ? 1 :0);        
+    

my $only_one = 2 == (! $x) + (! $y) + (! $z);

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The second two forms require each variable to be listed twice: 
my $only_one = ($x || $y || $z) && (! ($x && $y)) && (! ($y && $z)) &&
+ (! ($z && $x));

my $only_one = (! ($x && $y && $z)) && ($x ^ $y ^ $z);

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Just based on this criterion, I'd avoid the 2nd pair of solutions. (Looking at other replies, those with sub, map, grep, or List:Utils will take a list -- easier to maintain.)

-QM
--
Quantum Mechanics: The dreams stuff is made of

In reply to Re^2: One out of three ain't bad by QM
in thread One out of three ain't bad by saintmike

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