// @nuget: CommandLineParser -Version 2.6.0

using System;

using System.Collections.Generic;

using CommandLine;

using CommandLine.Text;

​

//Print Help Screen when Parser success

public class Program

{

    static ParserResult<Options> parserResult;

    public static void Main()

    {

        string[] args = new[]{"--stdin", "123"};

        Console.WriteLine("Call help screen when Parser success");

        var parser = new CommandLine.Parser(with => with.HelpWriter = null);

        parserResult = Parser.Default.ParseArguments<Options>(args);

        parserResult.WithParsed(Run).WithNotParsed(errs => HandleErrors(errs));

    }

​

    static void HandleErrors(IEnumerable<Error> errs)

    {

        Console.WriteLine("Parser Fail");

    }

​

    private static void Run(Options options)

    {

        Console.WriteLine("parser SUCCESS");

        if (!validate(options))

        {

            Console.WriteLine("Validation fail");

            var helpText = GetHelp<Options>(parserResult);

            Console.WriteLine(helpText);

        }

    }

​

    //Generate Help text

    static string GetHelp<T>(ParserResult<T> result)

    {

        // use default configuration

        // you can customize HelpText and pass different configuratins

        //see wiki

        // https://github.com/commandlineparser/commandline/wiki/How-To#q1

        // https://github.com/commandlineparser/commandline/wiki/HelpText-Configuration

        return HelpText.AutoBuild(result, h => h, e => e);

    }

​

    //validate options

    static bool validate(Options options)

    {

        // do validation 

        if (options.FileName == null)

            return false;

        return true;

    }

}

​

class Options

{

    [Option(Default = false, HelpText = "Prints all messages to standard output.")]

    public bool Verbose

    {

        get;

        set;

    }

​

    [Option("stdin", Default = false, HelpText = "Read from stdin")]

    public bool stdin

    {

        get;

        set;

    }

​

    [Option("file", HelpText = "File name")]

    public string FileName

    {

        get;

        set;

    }

​

    [Value(0, MetaName = "offset", HelpText = "File offset.")]

    public long? Offset

    {

        get;

        set;

    }

}