GREP_OPTIONS is deprecated in GNU grep since i think 2.20. It will be removed in a future version, and until then it's going to print an irritating warning mess

GREP_OPTIONS is deprecated in GNU grep since i think 2.20. It will be removed in a future version, and until then it's going to print an irritating warning message every time you use it. (I don't think there's any such plan for the various BSD greps, so if you use those exclusively you're probably fine.)