code: def validate_argv
      if ARGV.empty? then
        ARGV << "start"
      else
        if not %w{start stop restart zap status}.include? ARGV.first then
          $stderr.puts "ERROR: invalid command '#{ARGV.first}'"
          $stderr.puts
          $stderr.puts @opt_parser.help()
          exit 1
        end
      end
    end
docs: Validate ARGV
  
   If empty, default to "start", otherwise make sure we have a valid option
   for daemons.
  
   @raise [SystemExit] on invalid arg