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' but then you use the su command to change to 'user2':

command                 returned
who am I                user1
whoami                  user2

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