I don't see the point of initialising $!.

• Functions are free to change $! even if no error occurred, and do so. Whatever value you set won't stay there.

  $ echo foo | perl -le'$!=1; print 0+$!; <>; print 0+$!'
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• $! is meaningless unless a function notified you that it set $!. You can't read $! and compare it against the value you previously gave it. You would think the readline in the above example had failed.

• die will use $! if it's non-zero, but it will fall back to $?>>8 then to 255. If anything, that means $!=0; would be the best value with which to initialise $!.