Proper syntax for "id -r" command

-r must be used in conjunction with another option. For example:

$ id -Gr
1000 4 24 27 30 46 109 124

Quoting the man page:

-r, --real
print the real ID instead of  the  effective  ID,  with -ugG

The program and the docs deviate from standard practices:

If -ugG actually means -u|g|G[modifier] (which apparently it does), then it should be documented that way. The authors didn't seem to think it was worth the effort. However, when the user does the same thing (as Mr. Davis quite reasonably tried):

-ru, a legitimate, intuitive assumption, returns an error.

Apropos this tip:

stat -c "%U" $(tty)

Probably would have helped to mention that it's shell-specific.