Passing an associative array from c# to Powershell
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03-07-2019 - |
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?
Solution
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