Question

I have a similar, but different, question like How to redirect Powershell output from a script run by TaskScheduler and override default width of 80 characters.

I have a custom installer framework written long ago. Within it I can execute “tasks”. I recently had to add a task to execute a PowerShell script. Now, even though the task is written in C#, I cannot invoke the commands in the PowerShell script directly. That, unfortunately, is off the table.

In short, I want to invoke a PowerShell executable from C# and redirect its output back to my application. Here’s what I’ve done so far:

I can successfully invoke PowerShell using the following code (from a test project I created):

  string powerShellExeLocation = null;

  RegistryKey localKey = Registry.LocalMachine;

  RegistryKey subKey = localKey.OpenSubKey(@"SOFTWARE\Microsoft\PowerShell\1\PowerShellEngine");
  powerShellExeLocation = subKey.GetValue("ApplicationBase").ToString();

  if (!Directory.Exists(powerShellExeLocation))
    throw new Exception("Cannot locate the PowerShell dir.");

  powerShellExeLocation = Path.Combine(powerShellExeLocation, "powershell.exe");

  if (!File.Exists(powerShellExeLocation))
    throw new Exception("Cannot locate the PowerShell executable.");

  string scriptLocation = Path.Combine(Environment.CurrentDirectory, "PowerShellScript.ps1");

  if (!File.Exists(scriptLocation))
    throw new Exception("Cannot locate the PowerShell script.");

  ProcessStartInfo processInfo = new ProcessStartInfo();
  processInfo.Verb = "runas";
  processInfo.UseShellExecute = false;
  processInfo.RedirectStandardOutput = true;
  processInfo.RedirectStandardOutput = true;
  processInfo.WorkingDirectory = Environment.CurrentDirectory;

  processInfo.FileName = powerShellExeLocation;
  processInfo.Arguments = "-NoLogo -OutputFormat Text -NonInteractive -WindowStyle Hidden -ExecutionPolicy Unrestricted -File \"" + scriptLocation + "\" ";

  Process powerShellProcess = new Process();
  powerShellProcess.StartInfo = processInfo;
  powerShellProcess.OutputDataReceived += new DataReceivedEventHandler(powerShellProcess_OutputDataReceived);
  powerShellProcess.ErrorDataReceived += new DataReceivedEventHandler(powerShellProcess_ErrorDataReceived);

  powerShellProcess.Start();

  while (!powerShellProcess.HasExited)
  {
    Thread.Sleep(500);
  }

My handlers for the redirected output are never called:

void powerShellProcess_ErrorDataReceived(object sender, DataReceivedEventArgs e)

and

void powerShellProcess_OutputDataReceived(object sender, DataReceivedEventArgs e)

I am fairly confident that the script is running. Right now I just have a test script that is outputting the PATH contents.

$a = $env:path; $a.Split(";")

I tested this from within a PowerShell instance and it outputs correctly.

What can I do to get the PowerShell output to redirect to my C# code? I don’t want to rely on the scripts that I will execute to handle their own logging. I’d rather gather their output and handle it within the framework’s logging mechanism.

EDIT
Realized I left the odd loop thing to wait for exit in that code example. I’ve had the process “WaitForExit”:

powerShellProcess.WaitForExit();

EDIT
Using the suggestion from @MiniBill. I came up with the following code snippit:

powerShellProcess.Start();
while (!powerShellProcess.HasExited)
{
  string line;
  while (!string.IsNullOrEmpty((line = powerShellProcess.StandardOutput.ReadLine())))
    this.LogInfo("PowerShell running: " + line);
}

This handles the output fine. It’s cutting my lines at 80 characters :(, but I can live with that unless someone else can provide a suggestion to fix that!

UPDATE A Solution

/*
  * The next few lines define the process start info for the PowerShell executable.
  */
ProcessStartInfo processInfo = new ProcessStartInfo();
processInfo.Verb = "runas";
processInfo.UseShellExecute = false;
processInfo.RedirectStandardError = true;
processInfo.RedirectStandardOutput = true;
processInfo.WorkingDirectory = Environment.CurrentDirectory;

//this FileName was retrieved earlier by looking in the registry for key "HKLM\SOFTWARE\Microsoft\PowerShell\1\PowerShellEngine" and the value for "ApplicationBase"
processInfo.FileName = powerShellExeLocation;

//if we're going to use script arguments build up the arguments from the process start correctly.
if (!string.IsNullOrEmpty(this.ScriptArguments))
  processInfo.Arguments = "-NoLogo -NonInteractive -WindowStyle Hidden -ExecutionPolicy Unrestricted -File \"" + ScriptLocation + "\" '" + ScriptArguments + "'";
else
  processInfo.Arguments = "-NoLogo -NonInteractive -WindowStyle Hidden -ExecutionPolicy Unrestricted -File \"" + ScriptLocation + "\"";

//create the Process object, set the start info, and start the process
Process powerShellProcess = new Process();
powerShellProcess.StartInfo = processInfo;

powerShellProcess.Start();

/*
  * While the PowerShell process hasn't exited do the following:
  * 
  * Read from the current position of the StandardOutput to the end by each line and
  * update the tasks progress with this information
  * 
  * Read from the current position of StandardError to the end by each line, update
  * the task's progress with this information and set that we have an error.
  * 
  * Sleep for 250 milliseconds (1/4 of a sec)
  */
bool isError = false;
while (!powerShellProcess.HasExited)
{
  string standardOuputLine, standardErrorLine;
  while (!string.IsNullOrEmpty((standardOuputLine = powerShellProcess.StandardOutput.ReadLine())))
  {
    this.UpdateTaskProgress(standardOuputLine);
  }


  while (!string.IsNullOrEmpty((standardErrorLine = powerShellProcess.StandardError.ReadLine())))
  {
    this.UpdateTaskProgress(standardErrorLine);
    isError = true;
  }

  Thread.Sleep(250);
}

/*
  * Now that the process has completed read to the end of StandardOutput and StandardError.
  * Update the task progress with this information.
  */

string finalStdOuputLine = powerShellProcess.StandardOutput.ReadToEnd();
string finalStdErrorLine = powerShellProcess.StandardError.ReadToEnd();

if (!string.IsNullOrEmpty(finalStdOuputLine))
  this.UpdateTaskProgress(finalStdOuputLine);

if (!string.IsNullOrEmpty(finalStdErrorLine))
{
  this.UpdateTaskProgress(finalStdErrorLine);
  isError = true;
}

// there was an error during the run of PowerShell that was output to StandardError.  This doesn't necessarily mean that
// the script error'd but there was a problem.  Throw an exception for this.
if (isError)
  throw new Exception(string.Format(CultureInfo.InvariantCulture, "Error during the execution of {0}.", this.ScriptLocation));

Answer 1

You want to use the Process.StandardOutput property. It’s a stream that you can open to get the program’s output