Update src/dotnet_mytool/Program.cs

src/dotnet_mytool/Program.cs

@@ -0,0 +1,23 @@
+using System;
+using System.CommandLine;
+
+namespace DotNetMyTool
+{
+    class Program
+    {
+        static int Main(string[] args)
+        {
+            var rootCommand = new RootCommand();
+
+            var setEnvCommand = new Command("set-env", "Set an environment variable")
+            {
+                new Argument<string>("variable", "The environment variable in the format VAR_NAME=value"),
+                new Option<string>("--target", () => "User", "The target scope: User or Machine")
+            };
+
+            rootCommand.AddCommand(setEnvCommand);
+
+            return rootCommand.InvokeAsync(args).Result;
+        }
+    }
+}