Spike for reading environment variables from Registry in C# (avoids problems with refreshing environment values in process session chains)

Hello.RegEnv.cs

using System;
using System.Diagnostics;
using Microsoft.Win32;

namespace Hello.RegEnv
{
    class Program
    {
        static void Main(string[] args)
        {
            Debugger.Launch();

            var envVar = args[0];

            // This does not work from your installer shell when the installer added some new environment variables
            var expandedViaEnv = Environment.GetEnvironmentVariable(envVar);

            // This always gets the fresh and current environment value. This works with ClickOnce, too!
            var expandedViaReg = GetEnvVarFromRegistry(envVar);
            
            Console.WriteLine("{0} => {1} (Session)", envVar, expandedViaEnv);
            Console.WriteLine("{0} => {1} (Registry)", envVar, expandedViaReg);

            Console.WriteLine("Press any key.");
            Console.ReadKey();
        }

        private static object GetEnvVarFromRegistry(string envVar, string defaultValue = null)
        {
            var safeDefault = defaultValue ?? String.Empty;
            var value = (String)Registry.GetValue(@"HKEY_CURRENT_USER\Environment", envVar, safeDefault);
            if (value == safeDefault)
                value =
                    (String)Registry.GetValue(
                        @"HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment", envVar, safeDefault);
            return value;
        }
    }
}