getent group groupname
groups user
grep 'group-name-here' /etc/group
groups
groups userName-Here
groups
# to see the group joined by current user
$ id
groups
groups {USERNAME}
groups vivek
# this will display what groups the active user is in
groups
groups [user name]
# [user name] : (optionnal) the user to list the group of
# default is the one executing the command.
groups userName-Here