How do I get the name of the active user via the command line in OS X?

as 'whoami' has been obsoleted, it's probably more forward compatible to use:

id -un

I'm pretty sure the terminal in OS X is just like unix, so the command would be:

whoami

I don't have a mac on me at the moment so someone correct me if I'm wrong.

NOTE - The whoami utility has been obsoleted, and is equivalent to id -un. It will give you the current user

whoami

EDIT

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.

Via here

Checking the owner of /dev/console seems to work well.

stat -f "%Su" /dev/console

You can also use the logname command from the BSD General Commands Manual under Linux or MacOS to see the username of the user currently logged in, even if the user is performing a sudo operation. This is useful, for instance, when modifying a user's crontab while installing a system-wide package with sudo: crontab -u $(logname)

Per man logname:

LOGNAME(1)

NAME
    logname -- display user's login name

There are two ways-

whoami

or

echo $USER

If you want to know who's currently logged in to the system:

$ w
 15:56:14 up 5 days, 20:58,  6 users,  load average: 0.43, 0.53, 0.50
USER     TTY        LOGIN@   IDLE   JCPU   PCPU WHAT
me       pts/2     Fri19    1:03m  0.98s  0.98s -/bin/bash
me       pts/3     09:55    6:00m  0.43s  0.43s /bin/bash
me       pts/5     15:56    0.00s  0.23s  0.00s w

(This is from a Linux system; the formatting on OS X may be slightly different, but the information should be about the same.)

There may be multiple login sessions; UNIX is designed to be a multi-user system, after all.

getting username in MAC terminal is easy...

I generally use whoami in terminal...

For example, in this case, I needed that to install Tomcat Server...

Define 'active user'.

If the question is 'who is the logged in user', then 'who am i' or 'whoami' is fine (though they give different answers - 'whoami' reports just a user name; 'who am i' reports on terminal and login time too).

If the question is 'which user ID is the effective ID for the shell', then it is often better to use 'id'. This reports on the real and effective user ID and group ID, and on the supplementary group IDs too. This might matter if the shell is running SUID or SGID.

You can also retrieve it from the environment variables, but that is probably not secure, so I would go with Andrew's answer.

printenv USER

If you need to retrieve it from an app, like Node, it's easier to get it from the environment variables, such as

process.env.USER.