[.net] How can I run PowerShell with the .NET 4 runtime?

I am updating a PowerShell script that manages some .NET assemblies. The script was written for assemblies built against .NET 2 (the same version of the framework that PowerShell runs with), but now needs to work with .NET 4 assemblies as well as .NET 2 assemblies.

Since .NET 4 supports running applications built against older versions of the framework, it seems like the simplest solution is to launch PowerShell with the .NET 4 runtime when I need to run it against .NET 4 assemblies.

How can I run PowerShell with the .NET 4 runtime?

The other answers are from before 2012, and they focus on "hacking" PowerShell 1.0 or PowerShell 2.0 into targeting newer versions of the .NET Framework and Common Language Runtime (CLR).

However, as has been written in many comments, since 2012 (when PowerShell 3.0 came) a much better solution is to install the newest version of PowerShell. It will automatically target CLR v4.0.30319. This means .NET 4.0, 4.5, 4.5.1, 4.5.2, or 4.6 (expected in 2015) since all of these versions are in-place replacements of each other. Use $PSVersionTable or see the Determine installed PowerShell version thread if you are unsure of your PowerShell version.

At the time of writing, the newest version of PowerShell is 4.0, and it can be downloaded with the Windows Management Framework (Google search link).

The best solution I have found is in the blog post Using Newer Version(s) of .NET with PowerShell. This allows powershell.exe to run with .NET 4 assemblies.

Simply modify (or create) $pshome\powershell.exe.config so that it contains the following:

<?xml version="1.0"?> 
<configuration> 
    <startup useLegacyV2RuntimeActivationPolicy="true"> 
        <supportedRuntime version="v4.0.30319"/> 
        <supportedRuntime version="v2.0.50727"/> 
    </startup> 
</configuration> 

Additional, quick setup notes:

Locations and files are somewhat platform dependent; however will give you an inline gist of how to make the solution work for you.

• You can find PowerShell's location on your computer by executing cd $pshome in the Powershell window (doesn't work from DOS prompt).
  • Path will be something like (example) C:\Windows\System32\WindowsPowerShell\v1.0\
• The filename to put configuration in is: powershell.exe.config if your PowerShell.exe is being executed (create the config file if need be).
  • If PowerShellISE.Exe is running then you need to create its companion config file as PowerShellISE.Exe.config

Please be VERY careful with using the registry key approach. These are machine-wide keys and forcibily migrate ALL applications to .NET 4.0.

Many products do not work if forcibily migrated and this is a testing aid and not a production quality mechanism. Visual Studio 2008 and 2010, MSBuild, turbotax, and a host of websites, SharePoint and so on should not be automigrated.

If you need to use PowerShell with 4.0, this should be done on a per-application basis with a configuration file, you should check with the PowerShell team on the precise recommendation. This is likely to break some existing PowerShell commands.

Just as another option, the latest PoshConsole release includes binaries targeted to .NET 4 RC (which work fine against the RTM release) without any configuration.

Here is the contents of the configuration file I used to support both .NET 2.0 and .NET 4 assemblies:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <!-- http://msdn.microsoft.com/en-us/library/w4atty68.aspx -->
  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0" />
    <supportedRuntime version="v2.0.50727" />
  </startup>
</configuration>

Also, here’s a simplified version of the PowerShell 1.0 compatible code I used to execute our scripts from the passed in command line arguments:

class Program {
  static void Main( string[] args ) {
    Console.WriteLine( ".NET " + Environment.Version );

    string script = "& " + string.Join( " ", args );
    Console.WriteLine( script );
    Console.WriteLine( );

    // Simple host that sends output to System.Console
    PSHost host = new ConsoleHost( this );
    Runspace runspace = RunspaceFactory.CreateRunspace( host );

    Pipeline pipeline = runspace.CreatePipeline( );
    pipeline.Commands.AddScript( script );

    try {
      runspace.Open( );
      IEnumerable<PSObject> output = pipeline.Invoke( );
      runspace.Close( );

      // ...
    }
    catch( RuntimeException ex ) {
      string psLine = ex.ErrorRecord.InvocationInfo.PositionMessage;
      Console.WriteLine( "error : {0}: {1}{2}", ex.GetType( ), ex.Message, psLine );
      ExitCode = -1;
    }
  }
}

In addition to the basic error handling shown above, we also inject a trap statement into the script to display additional diagnostic information (similar to Jeffrey Snover's Resolve-Error function).

If you only need to execute a single command, script block, or script file in .NET 4, try using Activation Configuration Files from .NET 4 to start only a single instance of PowerShell using version 4 of the CLR.

Full details:

http://blog.codeassassin.com/2011/03/23/executing-individual-powershell-commands-using-net-4/

An example PowerShell module:

https://gist.github.com/882528

Actually, you can get PowerShell to run using .NET 4 without affecting other .NET applications. I needed to do so to use the new HttpWebRequest "Host" property, however changing the "OnlyUseLatestCLR" broke Fiddler as that could not be used under .NET 4.

The developers of PowerShell obviously foresaw this happening, and they added a registry key to specify what version of the Framework it should use. One slight issue is that you need to take ownership of the registry key before changing it, as even administrators do not have access.

• HKLM:\Software\Microsoft\Powershell\1\PowerShellEngine\RuntimeVersion (64 bit and 32 bit)
• HKLM:\Software\Wow6432Node\Microsoft\Powershell\1\PowerShellEngine\RuntimeVersion (32 bit on 64 bit machine)

Change the value of that key to the required version. Keep in mind though that some snapins may no longer load unless they are .NET 4 compatible (WASP is the only one I have had trouble with, but I don't really use it anyway). VMWare, SQL Server 2008, PSCX, Active Directory (Microsoft and Quest Software) and SCOM all work fine.

Just run powershell.exe with COMPLUS_version environment variable set to v4.0.30319. For example, from cmd.exe or .bat-file:

set COMPLUS_version=v4.0.30319
powershell -file c:\scripts\test.ps1

If you're still stuck on PowerShell v1.0 or v2.0, here is my variation on Jason Stangroome's excellent answer.

Create a powershell4.cmd somewhere on your path with the following contents:

@echo off
:: http://stackoverflow.com/questions/7308586/using-batch-echo-with-special-characters
if exist %~dp0powershell.exe.activation_config goto :run
echo.^<?xml version="1.0" encoding="utf-8" ?^>                 > %~dp0powershell.exe.activation_config
echo.^<configuration^>                                        >> %~dp0powershell.exe.activation_config
echo.  ^<startup useLegacyV2RuntimeActivationPolicy="true"^>  >> %~dp0powershell.exe.activation_config
echo.    ^<supportedRuntime version="v4.0"/^>                 >> %~dp0powershell.exe.activation_config
echo.  ^</startup^>                                           >> %~dp0powershell.exe.activation_config
echo.^</configuration^>                                       >> %~dp0powershell.exe.activation_config
:run
:: point COMPLUS_ApplicationMigrationRuntimeActivationConfigPath to the directory that this cmd file lives in
:: and the directory contains a powershell.exe.activation_config file which matches the executable name powershell.exe
set COMPLUS_ApplicationMigrationRuntimeActivationConfigPath=%~dp0
%SystemRoot%\System32\WindowsPowerShell\v1.0\powershell.exe %*
set COMPLUS_ApplicationMigrationRuntimeActivationConfigPath=

This will allow you to launch an instance of the powershell console running under .NET 4.0.

You can see the difference on my system where I have PowerShell 2.0 by examining the output of the following two commands run from cmd.

C:\>powershell -ExecutionPolicy ByPass -Command $PSVersionTable

Name                           Value
----                           -----
CLRVersion                     2.0.50727.5485
BuildVersion                   6.1.7601.17514
PSVersion                      2.0
WSManStackVersion              2.0
PSCompatibleVersions           {1.0, 2.0}
SerializationVersion           1.1.0.1
PSRemotingProtocolVersion      2.1


C:\>powershell4.cmd -ExecutionPolicy ByPass -Command $PSVersionTable

Name                           Value
----                           -----
PSVersion                      2.0
PSCompatibleVersions           {1.0, 2.0}
BuildVersion                   6.1.7601.17514
CLRVersion                     4.0.30319.18408
WSManStackVersion              2.0
PSRemotingProtocolVersion      2.1
SerializationVersion           1.1.0.1

If you don't want to modify the registry or app.config files, an alternate way is to create a simple .NET 4 console app that mimicks what PowerShell.exe does and hosts the PowerShell ConsoleShell.

See Option 2 – Hosting Windows PowerShell yourself

First, add a reference to the System.Management.Automation and Microsoft.PowerShell.ConsoleHost assemblies which can be found under %programfiles%\Reference Assemblies\Microsoft\WindowsPowerShell\v1.0

Then use the following code:

using System;
using System.Management.Automation.Runspaces;
using Microsoft.PowerShell;

namespace PSHostCLRv4
{
    class Program
    {
        static int Main(string[] args)
        {
            var config = RunspaceConfiguration.Create();
                return ConsoleShell.Start(
                config,
                "Windows PowerShell - Hosted on CLR v4\nCopyright (C) 2010 Microsoft Corporation. All rights reserved.",
                "",
                args
            );
        }
    }
}