This:

while( <> ) { ...
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...has special meaning in Perl. It's semantically equal to:

while( defined( $_ = <> ) ) { ...
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So your loop doesn't terminate upon reading a false value. It terminates when <> returns undef, which can happen when you reach the end of the file.

This is documented in perlop. It really is a special case. The implicit "defined" is just a "Do What I Mean" convenience.