docs: def signal(signal=None):
      '''
      Signals nginx to start, reload, reopen or stop.
  
      CLI Example:
  
      .. code-block:: bash
  
          salt '*' nginx.signal reload
      '''
      valid_signals = ('start', 'reopen', 'stop', 'quit', 'reload')
  
      if signal not in valid_signals:
          return
  
      # Make sure you use the right arguments
      if signal == "start":
          arguments = ''
      else:
          arguments = ' -s {0}'.format(signal)
      cmd = __detect_os() + arguments
      out = __salt__['cmd.run_all'](cmd)
  
      # A non-zero return code means fail
      if out['retcode'] and out['stderr']:
          ret = out['stderr'].strip()
      # 'nginxctl configtest' returns 'Syntax OK' to stderr
      elif out['stderr']:
          ret = out['stderr'].strip()
      elif out['stdout']:
          ret = out['stdout'].strip()
      # No output for something like: nginxctl graceful
      else:
          ret = 'Command: "{0}" completed successfully!'.format(cmd)
      return ret