Looking at the problem at the wrong level: Closing a process's stdin

Raymond Chen

Raymond

A customer was having trouble manipulating the stdin stream
that was given to a process.

How do you simulate sending Ctrl+Z to a hidden console process
programmatically?

I am using Redirect­Standard­Input
and want to send the console a Ctrl+Z.
I’ve tried sending ASCII code 26, but that doesn’t work.
Generate­Console­Ctrl­Event supports Ctrl+C
and
Ctrl+Break but not Ctrl+Z.

Here’s what I’m doing, but it doesn’t work:

ProcessStartInfo info = new ProcessStartInfo(@"...");
info.CreateNoWindow = true;
info.RedirectStandardError = true;
info.RedirectStandardOutput = true;
info.RedirectStandardInput = true;
info.UseShellExecute = false;
Process p = Process.Start(info);
// 0x1A is ASCII code of Ctrl+Z but it does not work
p.StandardInput.WriteLine("\x1A");

The customer was kind enough to do more than simply ask the
question.
The customer set up the scenario and even provided a code fragment
that illustrates the problem.
Which is good, because the original question was the wrong question.

The customer asked about simulating typing Ctrl+Z to a console,
but what they actually doing was sending a character to stdin;
they weren’t sending it to a console.
In fact, the way they created the process,
there is no console at all.

The customer confused stdin with consoles.
It’s true that Ctrl+Z is the convention used by console windows
to indicate that stdin should be closed.
But that is hardly any consolation when you took control of stdin yourself
and are not using a console window to manage it.

It’s like saying,
“Normally, when I want somebody to take my order,
I pull into a parking space and

turn on my headlights
,
and somebody will come out.
But I can’t get it to work.”

Um, that’s because you pulled into your own driveway.

Ctrl+Z is a convention used by console windows to indicate that
stdin should be closed, but if you said “I am going to manage stdin myself,”
then you aren’t using a console window,
and that convention carries no weight.
If you write a Ctrl+Z to the process’s stdin, it will simply read a Ctrl+Z.
But since you are managing stdin yourself,
you can do it yourself:
Just take the stream you set as the process’s stdin and

close it
.

Exercise:
Perhaps you can answer this related question from a different customer:

I am trying to send a Ctrl+C (SIGINT) to a process.

CurrentProcess = new Process();
CurrentProcess.StartInfo.FileName = "foo.exe";
CurrentProcess.StartInfo.UseShellExecute = false;
CurrentProcess.StartInfo.RedirectStandardInput = true;
StandardInputWriter = CurrentProcess.StandardInput;
char c = '\u0003';
StandardInputWriter.Write(c);
StandardInputWriter.Flush();
StandardInputWriter.Close();

If I launch the process from a command prompt and type
Ctrl+C, it flushes its output and terminates,
but when I start it from within my application and send
it a Ctrl+C via the code above,
the process is still running.
How do I send a Ctrl+C to a process?

Raymond Chen
Raymond Chen

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