That's true in most languages, if you're comparing whether or not a value is true or false, you don't have to explicitly add ' = true'. If you're unfamiliar with this concept, and how conditionals work, I'd strong recommend looking into general programming concepts. Not necessarily Perl, although if you're programming in Perl it would be a good place to start.
Learning these basic concepts will help you pick up any programming language in the future. The concepts don't change, but the syntax does, and that's just a matter of googling and forums.