How to run PowerShell scripts from C#

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Introduction

This article contains a bare-bones sample on how to add PowerShell scripting to your C# programs. To paraphrase that movie: "the Power of Shell compels you!"

Background

With the release of Windows PowerShell 1.0 in November 2006, we finally have a powerful command line shell for Windows, one that rivals or even exceeds the capabilities of the common Unix/Linux shells such as csh and bash. The reason for this is that PowerShell commands can read and write objects, as opposed to conventional shells that can only process strings of text. Because PowerShell runs on the .NET platform, the objects that are used are .NET objects, which makes it an ideal scripting language for .NET programs.

Prerequisites

Before you can compile the sample code, you'll need a couple of things. First of all, you have to install PowerShell itself, of course, which you can find at the following location: PowerShell homepage. The sample program also references some assemblies that aren't included with the standard PowerShell installation, so you'll have to get those by installing the Windows SDK for Windows Server 2008 and .NET Framework 3.5. Don't worry: even though the latter has 'Server 2008' in its name, it will also install on Vista and XP.

Using the Code

To add PowerShell scripting to your program, you first have to add a reference to the System.Management.Automation assembly. The SDK installs this assembly in the C:\Program Files\Reference Assemblies\Microsoft\WindowsPowerShell\v1.0 directory.

Then, you have to add the following 'using' statements to import the required types:

using System.Collections.ObjectModel;
using System.Management.Automation;
using System.Management.Automation.Runspaces;

The following code block shows the RunScript method that does all the hard work. It takes the script text, executes it, and returns the result as a string.

private string RunScript(string scriptText)
{
    // create Powershell runspace

    Runspace runspace = RunspaceFactory.CreateRunspace();

    // open it

    runspace.Open();

    // create a pipeline and feed it the script text

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

    // add an extra command to transform the script
    // output objects into nicely formatted strings

    // remove this line to get the actual objects
    // that the script returns. For example, the script

    // "Get-Process" returns a collection
    // of System.Diagnostics.Process instances.

    pipeline.Commands.Add("Out-String");

    // execute the script

    Collection<psobject /> results = pipeline.Invoke();

    // close the runspace

    runspace.Close();

    // convert the script result into a single string

    StringBuilder stringBuilder = new StringBuilder();
    foreach (PSObject obj in results)
    {
        stringBuilder.AppendLine(obj.ToString());
    }

    return stringBuilder.ToString();
}

How to Let the Script Interact with your Program

Before executing the script using the pipeline.Invoke() call, it's possible to expose the objects of your program to the script by using the method runspace.SessionStateProxy.SetVariable("someName", someObject). This will create a named variable that the script can access (getting/setting properties, and even calling methods). As an example, suppose we would expose the main form of the sample to the script by adding the SetVariable() call like this:

...
// open it

runspace.Open();
runspace.SessionStateProxy.SetVariable("DemoForm", this);
....

Then, the following script would print the caption of the window:

$DemoForm.Text

The following script would show all the properties and methods of the window:

$DemoForm | Get-Member

Please note, however, that any calls a script makes to your objects will be from another thread context, as pipeline.Invoke() seems to start its own worker thread. This means that your exposed objects will have to be thread-safe.

Points of Interest

As an extra feature, I added the ability to drag-n-drop a script on the form, so you don't have to copy-paste PowerShell scripts into the textbox all the time.

More Information on PowerShell

• See my second CodeProject PowerShell article for information on how to handle asynchronous execution of a script.
• Wikipedia on PowerShell

History

• Apr 01, 2007: First release
• Apr 04, 2007: Minor update
• Aug 28, 2008: Fixed the broken link to the SDK, and the broken link to my second powershell article