安利一款非常好用的命令行参数库：McMaster.Extensions.CommandLineUtils

static int Main(string[] args)
{
    var app = new CommandLineApplication{Name = "mdmeta"};
    app.HelpOption("-?|-h|--help");
    app.OnExecute(() =>
    {
        app.ShowHelp();
        return 0;
    });
    app.Command("echo", command =>
    {
        command.Description = "输出用户输入的文字。";
        command.HelpOption("-?|-h|-help");
        var wordsArgument = command.Argument("[words]", "指定需要输出的文字。");
        var repeatOption = command.Option("-r|--repeat-count", "指定输出重复次数", CommandOptionType.SingleValue);
        var upperOption = command.Option("--upper", "指定是否全部大写", CommandOptionType.NoValue);
        var separatorOption = command.Option("-s|--separator", "指定重复输出用户文字时重复之间应该使用的分隔符，可以指定多个，这将依次应用到每一次分割。", CommandOptionType.MultipleValue);
        command.OnExecute(() =>
        {
            // 在这里使用上面各种 Argument 和 Option 的 Value 或 Values 属性拿值。
            return 0;
        });
    });
    return app.Execute(new []{"-?"});
}

[CommandMetadata("echo", Description = "Output users command at specified format.")]
public sealed class SampleTask : CommandTask
{
    private int _repeatCount;

    [CommandArgument("[words]", Description = "The words the user wants to output.")]
    public string Words { get; set; }

    [CommandOption("-r|--repeat-count", Description = "Indicates how many times to output the users words.")]
    public string RepeatCountRaw
    {
        get => _repeatCount.ToString();
        set => _repeatCount = value == null ? 1 : int.Parse(value);
    }
    
    [CommandOption("--upper", Description = "Indicates that whether all words should be in upper case.")]
    public bool UpperCase { get; set; }

    [CommandOption("-s|--separator", Description = "Specify a string to split each repeat.")]
    public List<string> Separators { get; set; }

    public override int Run()
    {
        // 当用户敲入的命令已准备好，上面的参数准备好，那么这个函数就会在这里执行啦。
        return 0;
    }
}