Calling PowerShell cmdlet from C# throws CommandNotFoundException

Question

I'm trying to call the Add-AppxPackage cmdlet from C#. I found the MSDN article on running PowerShell from C# code. I have referenced the System.Management.Automation assembly and have tried the following code snippets, all of which result in the same exception when trying to call powerShell.Invoke():

System.Management.Automation.CommandNotFoundException was unhandled

The term 'Add-AppxPackage' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.

Snippet 1:

var powerShell = PowerShell.Create();
powerShell.AddCommand(string.Format("Add-AppxPackage '{0}'", appxFilePath));

foreach (PSObject result in powerShell.Invoke())
{
    Console.WriteLine(result);
}

I understand why this doesn't work, since I shouldn't be providing parameters in the AddCommand() function.

Snippet 2:

var powerShell = PowerShell.Create();
powerShell.AddCommand("Add-AppxPackage");
powerShell.AddParameter("Path", appxFilePath);

foreach (PSObject result in powerShell.Invoke())
{
    Console.WriteLine(result);
}

Snippet 3:

var powerShell = PowerShell.Create();
powerShell.AddCommand("Add-AppxPackage");
powerShell.AddArgument(appxFilePath);

foreach (PSObject result in powerShell.Invoke())
{
    Console.WriteLine(result);
}

My C# project targets .Net 4.5, and if I do powerShell.AddCommand("Get-Host") it works and the Version it returns back is 4.0. Add-AppxPackage was added in v3.0 of PowerShell, so the command should definitely exist, and it works fine if I manually run this command from the Windows PowerShell command prompt.

Any ideas what I am doing wrong here? Any suggestions are appreciated.

-- Update --

I found this post and this one, and realized there is a AddScript() function, so I tried this:

Snippet 4:

var powerShell = PowerShell.Create();
powerShell.AddScript(string.Format("Add-AppxPackage '{0}'", appxFilePath));

var results = powerShell.Invoke();
foreach (PSObject result in results)
{
    Console.WriteLine(result);
}

And it does not throw an exception, but it also doesn't install the metro app, and the "results" returned from powerShell.Invoke() are empty, so I'm still at a loss...

-- Update 2 --

So I decided that I would try just creating a new PowerShell process to run my command, so I tried this:

Process.Start(new ProcessStartInfo("PowerShell", string.Format("-Command Add-AppxPackage '{0}'; $key = $Host.UI.RawUI.ReadKey('NoEcho,IncludeKeyUp')", appxFilePath)));

but it still throws the same error that Add-AppxPackage is not a recognized cmdlet.

ANSWER

If you follow the long comment thread on robert.westerlund's answer, you will see that for some reason when running/launched from Visual Studio, PowerShell was not including all of the PSModulePaths that it does when running straight from a PowerShell command prompt, so many modules are not present. The solution was to find the absolute path of the module that I needed (the appx module in my case) using:

(Get-Module appx -ListAvailable).Path

And then import that module before trying to call one of its cmdlets. So this is the C# code that worked for me:

var powerShell = PowerShell.Create();
powerShell.AddScript(string.Format(@"Import-Module 'C:\WINDOWS\system32\WindowsPowerShell\v1.0\Modules\Appx\Appx.psd1'; Add-AppxPackage '{0}'", appxFilePath));
var results = powerShell.Invoke();

UPDATED ANSWER

You can see from this other post I opened, that the problem was with a bug in a Visual Studio extension (in my case StudioShell) causing not all of the PSModulePaths to be loaded. After uninstalling that extension all of the modules were loaded correctly and I no longer needed to manually import the module.

Answer 1

In PowerShell there is a difference between terminating errors (which stops the execution) and non-terminating errors (which are just written to the error stream).

If you want to create a non-terminating error in a function of your own, just use the Write-Error cmdlet. If you want to create a terminating error, use the Throw keyword. You can read more about these concepts if you run Get-Help Write-Error, Get-Help about_Throw and Get-Help about_Try_Catch_Finally.

Using the Add-AppxPackage with a non existing package is a non terminating error and will thus be written to the error stream, but no execution halting exception will be thrown. The following code tries to add a non existing package and then writes the error to the console.

var powerShell = PowerShell.Create();
powerShell.AddScript("Add-AppxPackage NonExistingPackageName");

// Terminating errors will be thrown as exceptions when calling the Invoke method. 
// If we want to handle terminating errors, we should place the Invoke call inside a try-catch block.
var results = powerShell.Invoke();

// To check if a non terminating error has occurred, test the HadErrors property
if (powerShell.HadErrors)
{
    // The documentation for the Error property states that "The command invoked by the PowerShell 
    // object writes information to this stream whenever a nonterminating error occurs."
    foreach (var error in powerShell.Streams.Error)
    {
        Console.WriteLine("Error: " + error);
    }
}
else
{
    foreach(var package in results)
    {
        Console.WriteLine(package);
    }
}