Create a new user via command line

To create a user:
$ sudo /System/Library/ServerSetup/serversetup -createUser fullname
shortname password
The name, short name, and password must be typed in the order shown. If the full
name includes spaces, type it in quotes.
The command displays a 1 if the full name or short name is already in use.

To create a user with a specific UID:
$ sudo /System/Library/ServerSetup/serversetup -createUserWithID
fullname shortname password userid
The name, short name, password, and UID must be typed in the order shown. If the full
name includes spaces, type it in quotes.
The command displays a 1 if the full name, short name, or UID is already in use or if the
UID you specified is less than 100.

To create a user with a specific UID and home directory:
$ sudo /System/Library/ServerSetup/serversetup -createUserWithIDIP
fullname shortname password userid homedirpath
The name, short name, password, and UID must be typed in the order shown. If the full
name includes spaces, type it in quotes.