Generate tab completions for shell command

generate_completions.sh

function _build_completions_helper {
  local current_word
	COMPREPLY=()
	current_word=${COMP_WORDS[COMP_CWORD]}
	COMPREPLY=($(compgen -W "${PROGRAM_COMMANDS}" -- $current_word))
	return 0
}

# param 1: command to build completions for. Ex: fab
#
# param 2: command that outputs all completable arguments for the app command
# (in param 1).
#
function _build_completions_for {
	app=$1
	command_list_call=$2

	PROGRAM_COMMANDS=$($command_list_call)
	complete -o nospace -F _build_completions_helper "$app"

}

# Example usage:
#_build_completions_for fab 'fab --shortlist'