groups - display current group names
The groups command displays the current group names or ID values. If the
value does not have a corresponding entry in /etc/group, the value will be
displayed as the numerical group value. The optional user parameter
will display the groups for the named user.
Systems which do not support concurrent group sets will have the information
from /etc/group reported. The user must use newgrp or sg to
change his current real and effective group ID.
Group account information.