Learning Perl, 5th Edition

The Ternary Operator, ?:

When Larry was deciding which operators to make available in Perl, he didn’t want former C programmers to miss something that C had and Perl didn’t, so he brought all of C’s operators over to Perl.^[‡] That meant bringing over C’s most confusing operator: the ternary ?: operator. While it may be confusing, it can also be quite useful.

The ternary operator is like an if-then-else test, all rolled into an expression. It is called a “ternary” operator because it takes three operands. It looks like this:

expression ? if_true_expr : if_false_expr

First, the expression is evaluated to see whether it’s true or false. If it’s true, the second expression is used; otherwise, the third expression is used. Every time, one of the two expressions on the right is evaluated, and one is ignored. That is, if the first expression is true, then the second expression is evaluated, and the third is ignored. If the first expression is false, then the second is ignored, and the third is evaluated as the value of the whole thing.

In this example, the result of the subroutine &is_weekend determines which string expression will be assigned to the variable:

my $location = &is_weekend($day) ? "home" : "work";

And here, we calculate and print out an average—or just a placeholder line of hyphens, if there’s no average available:

my $average = $n ? ($total/$n) : "-----";
print "Average: $average\n";

You could always rewrite any use of the ?: operator as an if structure, often much less conveniently ...