Your-first-app-with-System-CommandLine-DragonFruit.md

Building your first app with System.CommandLine.DragonFruit

This walkthrough will show you how to get started using the System.CommandLine.DragonFruit app model to build a command line application.

Create a new console app

Open a new console and run the following commands:

> dotnet new console -o myApp
> cd myApp

Install the System.CommandLine.DragonFruit package

Add some code

Open Program.cs. You'll see that your Main method looks like this:

static void Main(string[] args)
{
    Console.WriteLine("Hello World!");
}

If you run it, you'll see this:

> ./myapp # or: > dotnet run
Hello World!

The default main only takes string arguments as an array. With DragonFruit, you can accept named arguments of various types and specify default values. Change your Main method to this:

class Program
{
    /// <param name="intOption">An option whose argument is parsed as an int</param>
    /// <param name="boolOption">An option whose argument is parsed as a bool</param>
    /// <param name="fileOption">An option whose argument is parsed as a FileInfo</param>
    static void Main(int intOption = 42, bool boolOption = false, FileInfo fileOption = null)
    {
        Console.WriteLine($"The value for --int-option is: {intOption}");
        Console.WriteLine($"The value for --bool-option is: {boolOption}");
        Console.WriteLine($"The value for --file-option is: {fileOption?.FullName ?? "null"}");
    }
}

You're ready to run your program.

> dotnet run -- --int-option 123
The value for --int-option is: 123
The value for --bool-option is: False
The value for --file-option is: null

This program is equivalent to the one demonstrated in Your first app with System.CommandLine.

To explore its features, take a look at Features: overview