Ways to know the Logged in Username using Terminal [macOS/Linux/Unix]

In order to know the current user (username) who is logged in your an try one of the below commands on the Terminal.

1. Using whoami command:

# whoami
adam

Note:

# man whoami

NAME
     whoami – display effective user id

SYNOPSIS
     whoami

DESCRIPTION
     The whoami utility has been obsoleted by the id(1) utility, and is
     equivalent to “id -un”.  The command “id -p” is suggested for normal
     interactive use.

     The whoami utility displays your effective user ID as a name.
...

2. Using id command:

id is a command that you can use to return user identity.

id -un
adam

-u      Display the effective user ID as a number.

-n      Display the name of the user or group ID for the -G, -g and -u
        options instead of the number.  If any of the ID numbers cannot
        be mapped into names, the number will be displayed as usual.

3. Using $USER Environment Variable:

# echo $USER
adam