是否有向群组的所有成员发送私人消息的命令?

You can iterate through Guild.members.
When you receive a message that starts with /private, you take the rest and send it to every member of the guild by using Guild.members.forEach().
Here's a quick example:

client.on('message', msg => {
  if (msg.guild && msg.content.startsWith('/private')) {
    let text = msg.content.slice('/private'.length); // cuts off the /private part
    msg.guild.members.forEach(member => {
      if (member.id != client.user.id && !member.user.bot) member.send(text);
    });
  }
});

这只是一个基本的实现，您显然可以在命令检查中使用这个概念，或者通过添加额外的文本等来修改它.