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
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
Validate ARGV

 If empty, default to "start", otherwise make sure we have a valid option
 for daemons.

 @raise [SystemExit] on invalid arg