in reply to
Re^2: Reading files n lines a time
in thread Reading files n lines a time
Considering the OP deals with multi-GB files I'd prefer the slightly uglier assignment to $_ because the kite's tail is not optimized away so all the strings would actually be shoved through the binary negation twice.
I was surprised by the result BTW when I looked at the optree; I'm almost completely clueless about what Perl can and cannot optimize but it even a fairly trivial peephole optimizer as in early C compilers could catch this.