You have already received several good suggestions on how to suppress your warnings messages. I strongly suggest that you do not adopt any of them until you know what is causing the undefined data. It may be a symptom of a more serious problem. In that case, fixing the underlying problem would probably eliminate the warnings. Only hide the warnings if you know that the undefined data fields are valid and that your grep handles them properly. If you know that they are invalid and you cannot remove them sooner, use hippo's pre-filter (Re^3: "Use of uninitialized value in pattern match (m//)" warning, doing a grep on 2D array) to remove them.