Unknown commands don't say they are so, commands you can't use are unknown.

[Anna Bakker]

Using real unknown commands don't say anything in chat, but using commands you are not allowed to use say unknown command.

For example, if I was to type "/abcdefg" in chat, it wouldn't say "Unknown command" and it would do nothing at all.

But if I were to type something like "/effect", "/give", "/item", "/spawnmob", "/god", "/mode", "/gamemode" or "/tellraw" all of those would tell me "Unknown command" in rose red text in my chat.

Though some commands say "You are not allowed to do that!" in rose red text. Some examples of these are "/admin", "/fly", "/grassify" or "/area"

Most donor commands used (if you don't have permission to) still say "You don't have permission for this." in rose red text. Besides a few such as /grassify.

There is also a few commands that say "You are not allowed to do that!" in dark red text, instead of the normal rose red text all the others have. A example of this command is "/weather".

Worldedit commands such as "//", "//fill", "//paste" come up with "You don't have permission to do this." in rose red text.

This is probably because of the different plugins using different messages, though it is slightly annoying when you mistype a command such as "/gcheck" or something similar and you think it is just taking it's time as it doesn't say anything in chat. And also the commands which are real commands saying "Unknown command" just because I don't have permission to them :)

[Riot]

This is a mish-mash of reports for different issues, but none of them concern scripts.

It is indeed up to each plugin how it reports if there are inadequate permissions for a command. Some such as worldedit try to emulate the default "no such command" message, which is obviously missing here.

If you want to report that worldedit says "unknown command" instead of "you aren't allowed to do that", report that on the worldedit tracker.

If you want to report that classicloader or exec do not give correct responses if there are inadequate permissions, please report that on classicloader and exec's tracker.

If you want to report that canary fails to give messages for actually missing commands, report that to canary directly.

In this case, you should probably do all four.