using System;

using System.CommandLine;

public class Program

{

    public static void Main()

    {

        var option = new Option<string[]>("-o") { Arity = ArgumentArity.OneOrMore };

        // var option = new Option<string[]>("-o") { Arity = new ArgumentArity(3,3) };     // <--- this doesn't work either

​

        var rootCmd = new RootCommand

        {

            option

        };

​

        rootCmd.SetHandler(

            (string[] o) =>

            {

                for (int i = 0; i < o.Length; ++i)

                    Console.WriteLine($"Value {i+1}: {o[i]}");

            },

            option

        );

​

​

        var cmdLine = "-o a -o b -o c";

        Console.WriteLine($"Commandline: {cmdLine}");

        rootCmd.Invoke(cmdLine);

​

        Console.WriteLine();

        Console.WriteLine("--------------------------------------------");

        Console.WriteLine();

​

        cmdLine = "-o a b c";

        Console.WriteLine($"Commandline: {cmdLine}");

        rootCmd.Invoke(cmdLine);

    }

}