[.net] What's the foolproof way to tell which version(s) of .NET are installed on a production Windows Server?

If you want to find versions prior to .NET 4.5, use code for a console application. Like this:

using System;
using System.Security.Permissions;
using Microsoft.Win32;

namespace findNetVersion
{
    class Program
    {
        static void Main(string[] args)
        {
            using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine,
                     RegistryView.Registry32).OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\"))
            {
                foreach (string versionKeyName in ndpKey.GetSubKeyNames())
                {
                    if (versionKeyName.StartsWith("v"))
                    {

                        RegistryKey versionKey = ndpKey.OpenSubKey(versionKeyName);
                        string name = (string)versionKey.GetValue("Version", "");
                        string sp = versionKey.GetValue("SP", "").ToString();
                        string install = versionKey.GetValue("Install", "").ToString();
                        if (install == "") //no install info, must be later version
                            Console.WriteLine(versionKeyName + "  " + name);
                        else
                        {
                            if (sp != "" && install == "1")
                            {
                                Console.WriteLine(versionKeyName + "  " + name + "  SP" + sp);
                            }
                        }
                        if (name != "")
                        {
                            continue;
                        }
                        foreach (string subKeyName in versionKey.GetSubKeyNames())
                        {
                            RegistryKey subKey = versionKey.OpenSubKey(subKeyName);
                            name = (string)subKey.GetValue("Version", "");
                            if (name != "")
                                sp = subKey.GetValue("SP", "").ToString();
                                install = subKey.GetValue("Install", "").ToString();
                            if (install == "") //no install info, ust be later
                                Console.WriteLine(versionKeyName + "  " + name);
                            else
                            {
                                if (sp != "" && install == "1")
                                {
                                    Console.WriteLine("  " + subKeyName + "  " + name + "  SP" + sp);
                                }
                                else if (install == "1")
                                {
                                    Console.WriteLine("  " + subKeyName + "  " + name);
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

Otherwise you can find .NET 4.5 or later by querying like this:

private static void Get45or451FromRegistry()
{
    using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine,
       RegistryView.Registry32).OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full\"))
    {
        int releaseKey = (int)ndpKey.GetValue("Release");
        {
            if (releaseKey == 378389)

                Console.WriteLine("The .NET Framework version 4.5 is installed");

            if (releaseKey == 378758)

                Console.WriteLine("The .NET Framework version 4.5.1  is installed");

        }
    }
}

Then the console result will tell you which versions are installed and available for use with your deployments. This code come in handy, too because you have them as saved solutions for anytime you want to check it in the future.

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