private final List<CommandRegistry> commandRegistries;

    public ShellCommandRegistryHolder() {
        this.commandRegistries = new ArrayList<>();
    }

    public void addCommandRegistry(CommandRegistry commandRegistry) {
        requireNonNull(commandRegistry, "commandRegistry");
        this.commandRegistries.add(commandRegistry);
    }

    public CommandRegistry[] getCommandRegistries() {

        holder.addCommandRegistry(builtins);

        // gather commands
        Map<String, ShellCommandRegistryFactory> factories =
                context.lookup.lookupMap(ShellCommandRegistryFactory.class);
        for (Map.Entry<String, ShellCommandRegistryFactory> entry : factories.entrySet()) {
            holder.addCommandRegistry(entry.getValue().createShellCommandRegistry(context));
        }