I think the only time folks would "frown upon" the use of  local $/; (which sets a local copy of the variable to "undef" without having to actually mention undef), would be if this were done at a point in your script that has global scope, which sort of defeats the purpose of using the "local" keyword.

(Well, some nit-pickers would also object to doing this when you don't actually use "readline()" or the diamond operator.)