Creating users on OSX 10.5 and up from the command line

Use the dscl command. This example would create the user "luser", like so:

dscl . -create /Users/luser
dscl . -create /Users/luser UserShell /bin/bash
dscl . -create /Users/luser RealName "Lucius Q. User"
dscl . -create /Users/luser UniqueID "1010"
dscl . -create /Users/luser PrimaryGroupID 80
dscl . -create /Users/luser NFSHomeDirectory /Users/luser

You can then use passwd to change the user's password, or use:

dscl . -passwd /Users/luser password

You'll have to create /Users/luser for the user's home directory and change ownership so the user can access it, and be sure that the UniqueID is in fact unique.

This line will add the user to the administrator's group:

dscl . -append /Groups/admin GroupMembership luser

which will search your path for the arguments you supply, it's found on just about any BSD or SysV UNIX

moriarty:~ dave$ which bash true false
/bin/bash
/usr/bin/true
/usr/bin/false