GNU grep doesn't take a value for `-E`, so it interprets this as `grep -i -E -t`, which explains the error. It doesn't have a `-t` option. I don't know of any

GNU grep doesn't take a value for `-E`, so it interprets this as `grep -i -E -t`, which explains the error. It doesn't have a `-t` option. I don't know of any grep that does take a value for `-E`. It does support taking a value for `-f`, and it also does support that as the last option in a group: grep -qf/path/to/file works, even if path is something like "patterns" (see that "t" in there?). >So, once again: what is "correct", when it comes to option handling? Your example was grep, but by the examples of other GNU tools, it only does an "approximation". I believe you're simply mistaken about what options it takes, and which options take values, the parsing seems "correct".