My, my, my. Another fool who thinks he can appear to be smart by chiming the familiar song about map in void context. And to be really smart he mentions it's not so bad in modern perl.

Forget about the map. The damage is done before the map is called. Executing <> in list context is slurping in the entire file. You've lost your constant memory solution right there. Regardless of the version of Perl you are using.