How to find out what group a given user has?
This one shows the user's uid as well as all the groups (with their gids) they belong to
id userid
On Linux/OS X/Unix to display the groups to which you (or the optionally specified user) belong, use:
id -Gn [user]which is equivalent to groups [user] utility which has been obsoleted on Unix.
On OS X/Unix, the command id -p [user] is suggested for normal interactive.
Explanation on the parameters:
-G,--groups- print all group IDs
-n,--name- print a name instead of a number, for-ugG
-p- Make the output human-readable.