A simple command line interface

ICommand.cs

namespace TestApp
{
    public interface ICommand
    {
        void Execute();
    }
}

Ls.cs

using System;

namespace TestApp
{
    public class Ls : ICommand
    {
        public void Execute()
        {
            Console.WriteLine("file1\tfile2\tfile3");
        }
    }
}

Program.cs

using System;
using System.Collections.Generic;

namespace TestApp
{
    internal class Program
    {

        private static Dictionary<string, ICommand> commands = new Dictionary<string, ICommand> {
            {"ls", new Ls()}, {"cd", null}, {"pwd", null}   // replace the nulls with command classes
        };

        public static void Main()
        {
            string command;

            while (true) {
                command = Console.ReadLine();
                if (command.Equals("exit")) break;
                if (!commands.ContainsKey(command))
                    Console.WriteLine("Invalid command");
                else commands[command].Execute();
            }
        }

    }
}