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I am using the Process class to run an exe.

The exe is a 3rd party console application that I do not control.

I wish to know whether the process is waiting for input on the command line.

Should it make any difference, I intend to kill the application should it be waiting for input.

There are suitable events for when there is output from the program waiting to be read, but I cannot see anything similar for when the process is waiting patiently for input.

            ProcessStartInfo info = new ProcessStartInfo();
            info.FileName = "myapp.exe";
            info.CreateNoWindow = true;
            info.UseShellExecute = false;
            info.RedirectStandardError = true;
            info.RedirectStandardInput = true;
            info.RedirectStandardOutput = true;
            process.StartInfo = info;

            process.OutputDataReceived += new DataReceivedEventHandler(process_OutputDataReceived);
            process.ErrorDataReceived += new DataReceivedEventHandler(process_ErrorDataReceived);

            process.Start();

            process.BeginOutputReadLine();
            process.BeginErrorReadLine();


            process.WaitForExit();

How do I detect that my process is waiting for input?

Don Vince
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  • Your problem rises my interest. I made some quirks to detect modal loops in GUI applications (see my questions) but for console applications, so far I did not find a good solution yet... – jdehaan Nov 10 '09 at 00:08

3 Answers3

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Depending on what the 3rd party process is doing exactly you could try polling its threads' states:

foreach(ProcessThread thread in process.Threads)
    if (thread.ThreadState == ThreadState.Wait
        && thread.WaitReason == ThreadWaitReason.UserRequest)
            process.Kill();

Failing that... you can try to 

process.StandardInput.Close();

after calling Start(), I conjecture that an exception will be raised in the child process if it's trying to read from standard input.

Serguei
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  • This appears to work in my test rig. I'll try it vs. the actual program causing me problems next. For info: Using process.StandardInput.Close() my program being run didn't receive an exception, it just stopped running quietly. – Don Vince Nov 10 '09 at 15:40
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    I discovered today that you want to check if the `WaitReason` is `ThreadWaitReason.LpcReply`. – Aaron Jensen Oct 08 '13 at 00:58
2

If the console application has some sort of prompt waiting for input, you could periodically parse out the console output text using the Process.StandardOutput property of the process and wait for said prompt. Once the proper string is detected, you know that it's waiting for input. See http://msdn.microsoft.com/en-us/library/system.diagnostics.process.standardoutput.aspx.

nithins
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  • Great approach. It doesn't address my issue, but is a valid approach for situations where you can bank on the output. Thanks again. – Don Vince Nov 10 '09 at 15:41
  • Though this may not always work as some console programs wont flush the user prompt to the console until after it gets a response. – Peter Jamsmenson Dec 26 '14 at 09:17
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Use process.StandardInput.writrLine("input"); for sending input to consol in c#

Rahul Rathaur
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