Make sure you understand your logic..as programming logical operators (and not or) behave sometimes a bit differently to what one might intend or write in spoken language terms. So if you actually want lines that match "MOD" or "DEL" to show up in your output, you need to have a OR operator. Using AND operator will only ever show lines that have both match strings on the same line.
the hardest line to type correctly is: stty erase ^H