$count += s/\b$oldline\b/$spliced/eg for @array;

A small point: I don't understand why you're using the  /e modifier in this substitution. It "works" (i.e., produces the same result) just as well with it as without, but if you're concerned about speed, I don't see how firing up the interpreter for each and every substitution is going to help. Is  $spliced just a placeholder for significant code that you don't want to show?