Apex supports command and function name autocompletion. To enable this functionality you'll need to add the following shell script to your profile or similar:
_apex() {
COMPREPLY=()
local cur="${COMP_WORDS[COMP_CWORD]}"
local opts="$(apex autocomplete -- ${COMP_WORDS[@]:1})"
COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
return 0
}
complete -F _apex apex