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;

[download]
I find it very useful in some of the 'log' wrappers I have written.

In reply to Re: "x ? y : z" notation by Ish
in thread "x ? y : z" notation by apok

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