eval would only "drop" something and populat $@ if something went wrong - that is, a "die" or a fatal error. But in the code you give, nothing goes wrong. Sure, print() and the implicite close() might return false values, but that doesn't mean the code dies. Hence, $@ will be undefined.

Beside that, I wouldn't use this construct. Sure, it might be safe in this simple case, but in general, you might have more code in the block. Which means that upon termination of the block, end-of-scope actions will be run. Lexical variables will go out of scope, DESTROY blocks might be run, and local variables will get their old values back. This might cause all kinds of library calls to happen, each of which might set $! (even if they succeed!)