w

w – display who is logged in and what they are doing.

Alvins-MacBook-Pro:~ alvin$ w
22:44  up 10 days,  9:31, 2 users, load averages: 2.02 1.84 1.77
USER     TTY      FROM              LOGIN@  IDLE WHAT
alvin    console  -                17Jul18 10days -
alvin    s001     -                22:30       - w