Run PowerShell script from C# writing to input pipe

Question

Hello,
I am trying to run a PowerShell script from C# (I have no control over what's in the script). The script may have a prompt like "Press enter to continue". So my goal is:
1. Get text output from the script (easy, many examples available)
3. If output contains "Press enter to continue", write a blank line to the running script's pipe to make it finish its job and quit
4. If output does contain that prompt, just let it exit by itself without sending any input
Note that commands in this PS script also try to get at script's file path, so I can't read script from file and pass it as text. It has to be executed as a script so it knows where it's located.
I have done this with .exes and batch files before. All you do in that case is process.StandardInput.WriteLine() which "types" enter into the input stream of script you are trying to control. But this does not work with Power Shell. How do I do this?
I have tried using PS object model like so:
using (Pipeline pipeline = runspace.CreatePipeline())
Command command = new Command(scriptPS, true, true);
   pipeline.Commands.Add(command);
   pipeline.Commands[0].MergeMyResults(PipelineResultTypes.Error, PipelineResultTypes.Output);
   pipeline.Input.Write("\n");
   Collection<PSObject> psresults = pipeline.Invoke();   //...
But I get an error because the script prompts:
"A command that prompts the user failed because the host program or the command type does not support user interaction. Try a host program that supports user interaction, such as the Windows PowerShell Console or Windows PowerShell ISE, and remove prompt-related
commands from command types that do not support user interaction, such as Windows PowerShell workflows."
I also tried using Process, and running PowerShell with -File switch to execute the script, then write to StandardInput with C#. I get no errors then, but the input is ignored and doesn't make it to PowerShell.
Please help!

Answer 1

No man, what kind of answer is that? You should have left it unanswered rather than waste people's time like this. I already seen those links before I posted my question. They address the issue of specifying script parameters, but not
writing to the input pipe.
Fortunately I did figure this out by writing a custom script host for PowerShell. Anyone interested can read about this in detail on MSDN (fortunately simple material with samples you can copy paste as I did, so this solution takes little time to implement).
Implement PSHost interface. Nothing special here, just paste directly from MSDN sample and modify their SetShouldExit function definition to contain just a "return;". Here's the relevant link:
http://msdn.microsoft.com/en-us/library/windows/desktop/ee706559(v=vs.85).aspx
Implement PSHostUserInterface interface. This is the ticket to solving this problem
(see below). Here's the MSDN link:
http://msdn.microsoft.com/en-us/library/windows/desktop/ee706584(v=vs.85).aspx
Implement PSHostRawUserInterface. This may not be required (not sure) but I did anyway. Nearly a direct paste from MSDN:
http://msdn.microsoft.com/en-us/library/windows/desktop/ee706601(v=vs.85).aspx
So, there are two PSHostUserInterface function implementations that are of particular interest. First is Prompt (read header comment to see why):
/// <summary>
/// When script attempts to get user input, we override it and give it input programmatically,
/// by looking up within promptInput's dictionary<string,string> or lineInput array.
/// PromptInput dictionary is mapped by input prompt (for example, return "" in response to "Press ENTER to continue")
/// LineInput is a regular array, and each time the script wants to prompt for input we return the next line in that array;
/// this works much like piping inputs from a regular text file in DOS command line.
/// </summary>
/// <param name="caption">The caption or title of the prompt.</param>
/// <param name="message">The text of the prompt.</param>
/// <param name="descriptions">A collection of FieldDescription objects that
/// describe each field of the prompt.</param>
/// <returns>Throws a NotImplementedException exception.</returns>
public override Dictionary<string, PSObject> Prompt(string caption, string message, System.Collections.ObjectModel.Collection<FieldDescription> descriptions)
Dictionary<string, PSObject> ret = new Dictionary<string, PSObject>();
foreach (FieldDescription desc in descriptions)
if (this.promptInput.Count != 0)
ret[desc.Name] = new PSObject(this.promptInput[desc.Name] + "\r\n");
else if (this.lineInput != null && this.currentLineInput >= 0 && this.currentLineInput < this.lineInput.Length)
ret[desc.Name] = new PSObject(this.lineInput[this.currentLineInput++] + "\r\n");
else
if (desc.DefaultValue == null)
ret[desc.Name] = new PSObject("\r\n");
else
ret[desc.Name] = new PSObject(desc.DefaultValue);
return ret;
Next is PromptForChoice. Here I opted to always return the default choice, but you could rewrite it to read from somewhere to "simulate" reading from input pipe just like the function above:
public override int PromptForChoice(string caption, string message, System.Collections.ObjectModel.Collection<ChoiceDescription> choices, int defaultChoice)
        return defaultChoice;
Last but not least, here's a ReadLine implementation (again read header comment):
/// <summary>
/// If the LineInput is set, "read" the next line from line input string array, incrementing line pointer/// </summary>
/// <returns>The characters that are entered by the user.</returns>
public override string ReadLine()
if (this.lineInput != null && this.currentLineInput >= 0 && this.currentLineInput < this.lineInput.Length)
return this.lineInput[this.currentLineInput++];
else
return Console.ReadLine();
Both are exposed as properties:
/// <summary>
/// Gets or sets the input pipe override
/// </summary>
public string Input
get
return string.Join("\n", this.lineInput);
set
if (value != null)
this.lineInput = value.Split('\n');
this.currentLineInput = 0;
else
this.lineInput = null;
/// <summary>
/// Gets or sets input pipe override for named prompts
/// </summary>
public Dictionary<string, string> PromptInput
get
return this.promptInput;
set
this.promptInput = value;
And finally, here's how the whole shebang is used:
/// <summary>
/// Runs a powershell script, with input pipe arguments
/// </summary>
/// <param name="script">Path of the script to execute, or script text</param>
/// <param name="inline">Whether or not to execute script text directly, or execute script from path</param>
/// <param name="unrestricted">Whether or not to set unrestricted execution policy</param>
/// <param name="parameters">Parameters to pass to the script command line</param>
/// <param name="inputOverride">Input to pass into the script's input pipe</param>
/// <param name="inputOverrideName">Input to pass into the script's input pipe, to each prompt by label</param>
/// <returns>Output lines</returns>
public static string PowerShell(string script, bool inline, bool unrestricted = false, Dictionary<string, string> parameters = null, string inputOverride = null, Dictionary<string, string> inputOverrideByName = null)
string output = null;
ScriptHost host = new ScriptHost();
(host.UI as ScriptHostUserInterface).Input = inputOverride;
(host.UI as ScriptHostUserInterface).PromptInput = inputOverrideByName;
using (Runspace runspace = RunspaceFactory.CreateRunspace(host))
runspace.Open();
if (unrestricted)
RunspaceInvoke runSpaceInvoker = new RunspaceInvoke(runspace);
runSpaceInvoker.Invoke("Set-ExecutionPolicy Unrestricted");
using (Pipeline pipeline = runspace.CreatePipeline())
if (inline)
pipeline.Commands.AddScript(script);
else
Command command = new Command(script, true, true);
foreach (KeyValuePair<string, string> param in parameters)
command.Parameters.Add(param.Key, param.Value);
pipeline.Commands.Add(command);
pipeline.Commands.Add("Out-String");
pipeline.Commands[0].MergeMyResults(PipelineResultTypes.Error, PipelineResultTypes.Output);
Collection<PSObject> psresults = pipeline.Invoke();
var sb = new StringBuilder();
foreach (PSObject obj in psresults)
sb.AppendLine(obj.ToString());
output = sb.ToString();
pipeline.Dispose();
runspace.Close();
return (host.UI as ScriptHostUserInterface).Output + "\r\n" + output;
As you can see, I also did some magic with the .Output property. That just accumulates lines of text output by the script in every WriteXXX function implemented in your custom PSHostUserInterface. The end result of all this, is that if you have a script
that has prompts, choices or reads from standard input, you can execute the script within the context of your custom script host written as above, to control precisely what strings are passed to it in response to prompts.