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Your first console app#

Let's create a calculator console application with Add & Subtract operations.

Your first step is to create a console application.

Begin by creating the commands:

public class Program
{
    // this is the entry point of your application
    static int Main(string[] args)
    {
        // AppRunner<T> where T is the class defining your commands
        // You can use Program or create commands in another class
        return new AppRunner<Program>().Run(args);
    }

    // Add command with two positional arguments
    public void Add(int x, int y) => Console.WriteLine(x + y);

    // Subtract command with two positional arguments
    public void Subtract(int x, int y) => Console.WriteLine(x - y);
}
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That's it. You now have an application with two commands. Let's see about how we can call it from command line.

Assuming our application's name is calculator.dll, let's run this app from command line using dotnet. First we'll check out the auto-generated help.

$ dotnet calculator.dll --help
Usage: dotnet calculator.dll [command]

Commands:

  Add
  Subtract

Use "dotnet calculator.dll [command] --help" for more information about a command.
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From the root we can see the available commands. Instead of --help we could have used -h or -?. We'll use -h to get help for the Add command.

$ dotnet calculator.dll Add -h
Usage: dotnet calculator.dll Add <x> <y>

Arguments:

  x  <NUMBER>

  y  <NUMBER>
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Let's try it out by adding two numbers

$ dotnet calculator.dll Add 40 20
60
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CommandDotNet will validate if the arguments can be converted to the correct type.

$ dotnet calculator.dll Add a 20
'a' is not a valid Number
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Note

Usage can be updated to support .exe or when run as a dotnet tool. See the UsageAppNameStyle & UsageAppName sections.

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