Discord.Net/samples/01_basic_ping_bot/Program.cs

using System;
using System.Threading.Tasks;
using Discord;
using Discord.WebSocket;

namespace _01_basic_ping_bot
{
    // This is a minimal, barebones example of using Discord.Net
    //
    // If writing a bot with commands, we recommend using the Discord.Net.Commands
    // framework, rather than handling commands yourself, like we do in this sample.
    //
    // You can find samples of using the command framework:
    // - Here, under the 02_commands_framework sample
    // - https://github.com/foxbot/DiscordBotBase - a barebones bot template
    // - https://github.com/foxbot/patek - a more feature-filled bot, utilizing more aspects of the library
    class Program
    {
        private DiscordSocketClient _client;

        // Discord.Net heavily utilizes TAP for async, so we create
        // an asynchronous context from the beginning.
        static void Main(string[] args)
            => new Program().MainAsync().GetAwaiter().GetResult();

        public async Task MainAsync()
        {
            _client = new DiscordSocketClient();

            _client.Log += LogAsync;
            _client.Ready += ReadyAsync;
            _client.MessageReceived += MessageReceivedAsync;

            // Tokens should be considered secret data, and never hard-coded.
            await _client.LoginAsync(TokenType.Bot, Environment.GetEnvironmentVariable("token"));
            await _client.StartAsync();

            // Block the program until it is closed.
            await Task.Delay(-1);
        }

        private Task LogAsync(LogMessage log)
        {
            Console.WriteLine(log.ToString());
            return Task.CompletedTask;
        }

        // The Ready event indicates that the client has opened a
        // connection and it is now safe to access the cache.
        private Task ReadyAsync()
        {
            Console.WriteLine($"{_client.CurrentUser} is connected!");

            return Task.CompletedTask;
        }

        // This is not the recommmended way to write a bot - consider
        // reading over the Commands Framework sample.
        private async Task MessageReceivedAsync(SocketMessage message)
        {
            // The bot should never respond to itself.
            if (message.Author.Id == _client.CurrentUser.Id)
                return;

            if (message.Content == "!ping")
                await message.Channel.SendMessageAsync("pong!");
        }
    }
}