Sorry, I missed that L, and I've never heard about JSONL before (although worked with JSON logs that are effectively JSONL). So, well, you may use grep, however it can be inefficient (depends on regex engine and how good you are in regexes). It is also easy to make a mistake if you are not very proficient in regexes. So I'd prefer using JSON parser (jq or another, maybe lower level if performance matters) over grep anyway.