To answer the question in your title (which is quite different from the question in your post), undef==$defined can indeed be true. It's true when $defined is zero when coerced into a number, since the numerical comparison operator (==) coerces its operands into numbers and undef is zero when coerced into a number.

See my reply in this recent thread for more details.

In reply to Re: undef==defined sometimes? (title question) by ikegami
in thread undef==defined sometimes? by perl-diddler

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