Question

I’d like to pass an associative array from C# to Powershell. As an example I’d like to execute this powershell line of code:

 PS C:\> get-command | select name, @{N='Foo';E={'Bar'}} -first 3  Name                                                        Foo ----                                                        --- Add-Content                                                 Bar Add-History                                                 Bar Add-Member                                                  Bar 

I’d like to do this via a Pipeline of distinct Commands as opposed to a single command marked as a script. Here’s the code:

 Runspace runspace = RunspaceFactory.CreateRunspace(); runspace.Open(); Pipeline pipeline = runspace.CreatePipeline();  pipeline.Commands.Add('get-command');  Command c = new Command('select-object'); List properties = new List(); properties.Add('name'); properties.Add('@{N=\'Foo\';E={\'Bar\'}}'); c.Parameters.Add('Property', properties.ToArray()); c.Parameters.Add('First', 3); pipeline.Commands.Add(c);  pipeline.Commands.Add('Out-String');  Collection retval = pipeline.Invoke(); runspace.Close();  StringBuilder stringBuilder = new StringBuilder(); foreach (PSObject obj in retval)     Console.WriteLine(obj.ToString()); 

But that associative array being passed in as a parameter to Select-Object isn’t being parsed correctly. This is what comes out the other side:

 PS C:\test> c:\test\Bin\Debug\test.exe  Name                                     @{N='Foo';E={'Bar'}} ----                                     -------------------- Add-Content Add-History Add-Member 

What’s wrong with how I’m setting up the Select-Object command parameters?

Answer 1

Creating a pipeline through c# and creating a pipeline with native powershell script have one major difference that is actually quite subtle: the parameter binder.

if I write a version of your code in pure script, I will get the same error: the hashtable literal is treated as a string value.

ps> $ps = $ps.Commands.Add('get-process') ps> $ps = $ps.Commands.Add('select-object') ps> $ps.Commands[1].Parameters.Add('Property', @('Name', '@{N='Foo';E={'Bar'}}')) 

In this case, the command receives an array of two strings, the ‘name’ and the hashtable literal string. This will be broken in exactly the same way as your C#. Now, take a look at the right way to do it (in script) – let me rewrite line 3:

ps> $ps.Commands[1].Parameters.Add('Property', @('Name', @{N='Foo';E={'Bar'}})) 

So what changed? I removed the quotes around the hashtable — I am passing a hashtable as the 2nd element of the object array! So, to get your C# example to work, you need to do what the parameter binder does for us at the command line (which is quite a lot!). Replace:

properties.Add('@{N=\'Foo\';E={\'Bar\'}}'); 

with

properties.Add(     new Hashtable {         {'N', 'Foo'},         {'E', System.Mananagement.Automation.ScriptBlock.Create('\'Foo\'')}     } ); 

I hope this clears it up for you. The parameter binder is probably the least visible but most powerful part of the powershell experience.

-Oisin