Using the whoami command

The whoami command displays a username associated with the effective user ID, unlike the who am I command, which displays the login name.

For example, if you login as user1 and then use the su command to change to 'user2':

command                 returned
who am I                user1
whoami                  user2

For more information about the whoami command, see whoami in z/OS UNIX System Services Command Reference.