Back in the day, the company I worked for required all newly hired system and software engineers to take their Unix Fundamentals class. 8 hours a day for 4 days they covered how the shell, coreutils, and filesystems work.
Sometimes people would complain that they didn't need a "beginner" class but I bet there wasn't a single person who didn't learn some important subtlety like how the trailing / works in different situations.
I've never had another company require or even offer a training like that. Do other companies still teach this stuff?
edit: typos