The newgrp command changes the group id and is equivalent to 'exec /bin/newgrp group'. In this example, the group id is changed from users to networks:
$ id uid=100(anatole) gid=101(users) $ newgrp networks uid=100(anatole) gid=12(networks)
Without arguments, newgrp resets the group-id to the default:
$ newgrp uid=100(anatole) gid=101(users)