This python script generates bash completion for all arguments of your ejabberdctl command.
Make sure that Ejabberd is running. If ejabberdctl command works everywhere just run [sudo] make. If you have installed Ejabberd in desired directory and ejabberdctl just works in there, run [sudo] make EJABBERDCTL_PATH=/path/to/ejabberd/bin/ (Do not miss / at the end of command).
then you can access your arguments using ejabberdctl <TAB>.