Write to stdin of a running process in windows

Question

I want to write data to an existing process's stdin from an external process in Windows.

I found similar questions for Linux, but I want to know how I can do the same in Windows.

How to write data to existing process's STDIN from external process?

How do you stream data into the STDIN of a program from different local/remote processes in Python?

https://serverfault.com/questions/443297/write-to-stdin-of-a-running-process-using-pipe

I tried with this code but I got an error. I also tried running the program, sending stdin to that with this code, but again, it errored.

In CMD:

type my_input_string | app.exe -start
my_input_string | app.exe -start
app.exe -start < pas.txt

In python:

p = subprocess.Popen('"C:\app.exe" -start', stdin=subprocess.PIPE, universal_newlines=True, shell=True)  
grep_stdout = p.communicate(input='my_input_string')[0]

The error I get is:

ReadConsole() failed: The handle is invalid.

And in C#:

try
{
    var startInfo = new ProcessStartInfo();
    startInfo.RedirectStandardInput = true;
    startInfo.FileName = textBox1.Text;
    startInfo.Arguments = textBox2.Text;
    startInfo.UseShellExecute = false;

    var process = new Process();
    process.StartInfo = startInfo;
    process.Start();
    Thread.Sleep(1000);
    var streamWriter = process.StandardInput;
    streamWriter.WriteLine("1");
}
catch (Exception ex)
{ 
    textBox4.Text = ex.Message+"\r\n"+ex.Source;
}

In C#, with the code above, App.exe (command line application which starts the other process) crashes, but in C# application I don't have any exception. I think that is because of UseShellExecute = false.

If I choose "don't run app in background" when I run the C# app, I can find the process and use sendkeys to send my_input_string to it, but this isn't a good idea because the user can see the commandline when it's running the GUI.

How can I send stdin, only using CMD, a python script, or C#, without any errors?

Answer 1

If you're launching, and then supplying the input from c#, you can do something like this:

var startInfo = new ProcessStartInfo("path/to/executable");
startInfo.RedirectStandardInput = true;
startInfo.UseShellExecute = false;

var process = new Process();
process.StartInfo = startInfo;
process.Start();

var streamWriter = process.StandardInput;
streamWriter.WriteLine("I'm supplying input!");

If you need to write to the standard input of an application already running, I doubt that is easy to do with .net classes, as the Process class will not give you the StandardInput (it will instead throw an InvalidOperationException)

Edit: Added parameter to ProcessStartInfo()

Answer 2

This question has been around for a while, but I hope it helps with the answer.

I needed to do something similar, using the aircrack-ng application suite, this suite receives a string through STDIN, the solution I found is available at this link: C# output string to aircrack-ng

Basically what you need is to start your python application, as a sub-process of the C# application.

Assuming that the python app is waiting for STDIN writing, it would look something like this:

public void WriteToAnotherProcess(string textToWrite)
{
    try
    {
        using (System.Diagnostics.Process FirstProcess = new System.Diagnostics.Process())
        {
            var startInfo = new ProcessStartInfo();

            startInfo.RedirectStandardOutput = true;
            startInfo.RedirectStandardInput = true;
            startInfo.FileName = textBox1.Text; // here the full path to the app that is waiting for the STDIN input
            startInfo.Arguments = textBox2.Text; //Arguments for second app
            startInfo.UseShellExecute = false;

            FirstProcess.StartInfo = startInfo;
            FirstProcess.Start();

            StreamWriter FirstProcessWriter = FirstProcess.StandardInput;
            StreamReader FirstProcessReader = FirstProcess.StandardOutput;

            FirstProcess.WriteLine(textToWrite);
            FirstProcess.Close();
            FirstProcess.WaitForExit();

            textBox4.Text = $"The return(STDOUT) from second app is: {FirstProcessReader.ReadToEnd()}";
        }
    }
    catch (Exception ex)
    {
        textBox4.Text = ex.Message + "\r\n" + ex.Source;
    }
}

If your application is crashing during execution, as you mentioned, you can use the property: RedirectStandardError available in ProcessStartInfo.

Getting the error return directly from the python application, so you will be able to understand what is really happening