From the ActiveState documentation of perlop
Conditional Operator
Ternary "?:" is the conditional operator, just as in C. It works much
+like an if-then-else. If the argument before the ? is true, the argum
+ent before the : is returned, otherwise the argument after the : is r
+eturned. For example:
printf "I have %d dog%s.\n", $n,
($n == 1) ? '' : "s";
Scalar or list context propagates downward into the 2nd or 3rd argumen
+t, whichever is selected.
$a = $ok ? $b : $c; # get a scalar
@a = $ok ? @b : @c; # get an array
$a = $ok ? @b : @c; # oops, that's just a count!
The operator may be assigned to if both the 2nd and 3rd arguments are
+legal lvalues (meaning that you can assign to them):
($a_or_b ? $a : $b) = $c;
Because this operator produces an assignable result, using assignments
+ without parentheses will get you in trouble. For example, this:
$a % 2 ? $a += 10 : $a += 2
Really means this:
(($a % 2) ? ($a += 10) : $a) += 2
Rather than this:
($a % 2) ? ($a += 10) : ($a += 2)
That should probably be written more simply as:
$a += ($a % 2) ? 10 : 2;
I find it very useful in some of the 'log' wrappers I have written.