It's tough to quantify the knowledge levels, but, I'd say that a practical understanding of bash loops, piping, grepping, and 'cut' ing text. Is a good start for basic dev work.

I've seen hours wasted writing jankey one off c++ utils, for lack of knowing that grep/awk exist.

Being able to tail a dev log and filter it for errors is also a part of seasoned developer competence too, I'd say.