id

User identity - display the user and group names (and IDs)
The groups utility has been obsoleted by id, and is equivalent to `id -Gn [user]'

SYNTAX
      id [user]
      id -G [-n] [user]
      id -P [user]
      id -g [-nr] [user]
      id -p [user]
      id -u [-nr] [user]

OPTIONS
   -G	   Display the different group IDs (effective, real and supplemen-
	   tary) as white-space separated numbers, in no particular order.

   -P	   Display the id as a password file entry.

   -g	   Display the effective group ID as a number.

   -n	   Display the name of the user or group ID for the -G, -g and -u
	   options instead of the number.  If any of the ID numbers cannot
	   be mapped into names, the number will be displayed as usual.

   -p	   Make the output human-readable.  If the user name returned by
	   getlogin(2) is different from the login name referenced by the
	   user ID, the name returned by getlogin(2) is displayed, preceded
	   by the keyword `login'.	The user ID as a name is displayed,
	   preceded by the keyword `uid'.  If the effective user ID is
	   different from the real user ID, the real user ID is displayed as
	   a name, preceded by the keyword `euid'.	If the effective group
	   ID is different from the real group ID, the real group ID is dis-
	   played as a name, preceded by the keyword `rgid'.  The list of
	   groups to which the user belongs is then displayed as names, pre-
	   ceded by the keyword `groups'.  Each display is on a separate
	   line.

   -r	   Display the real ID for the -g and -u options instead of the
	   effective ID.

   -u	   Display the effective user ID as a number.   

Displays the user and group names and numeric IDs, of the calling process, to the standard output.

If the real and effective IDs are different, both are displayed, otherwise only the real ID is displayed.

If a user (login name or user ID) is specified, the user and group IDs of that user are displayed. In this case, the real and effective IDs are assumed to be the same.

"There is no monument dedicated to the memory of a committee" - Lester J. Pourciau

Related commands:

The historic groups command is equivalent to `id -Gn [user]'
The historic whoami command is equivalent to `id -un'
who - Print all users currently logged in
who am i - Print real user name.

Equivalent BASH command:

who - Print all users currently logged in