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

Question

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?

Answer 1

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).

Answer 2

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.

Answer 3

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.

Answer 4

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