Mostly what AnomalousMonk said. The first paragraph on ?: in Programming Perl (4th ed) talks about it being an operator and expression similar to if-then-else which is a flow control statement. A hopefully simpler example:

use Modern::Perl;

my $count = 0;
print   defined $count
            ? do {
                my $s = '';
                $s .= '=' until $count++ == 10;
                $s
            }
            : "Undefined count.\n";
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