C# – ProcessInfo and RedirectStandardOutput


I have an app which calls another process in a command window and that process has updating stats that output to the console window. I thought this was a fairly simple operation but I can't seem to get it to work. Am I missing something?

string assemblyLocation = Assembly.GetExecutingAssembly().Location;

Process process = new Process
    ProcessStart =
        RedirectStandardOutput = true,
        UseShellExecute = false,
        WindowStyle = ProcessWindowStyle.Hidden,
        Arguments = arg,
        FileName = assemblyLocation.Substring(0, assemblyLocation.LastIndexOf("\\")) + "\\ffmpeg.exe",
        CreateNoWindow = true




Ideally what I would like is as the output changes within that process I hit or data comes into the reader that I get events off it.

Any help would be great, I feel like this is a newbie question but seem to be missing something.

Best Answer

I've experienced this before. Sometimes, the way in which the process you're calling outputs to the console is not compatible with this sort of output redirection. I've been fortunate enough in this case to be able to modify the external process to get around this.

You might try running your code on another process that outputs to the console, and see if it works properly. It reads about right to me right now.


I went and pulled a code block I've used to do this. This is in a WPF app which redirects the process output to the window. Notice the event binding. Since this is WPF I have to invoke my call to write the data out. Since you aren't worried about blocking, ou should be able to simply replace that with:


Hopefully it helps!

    private static void LaunchProcess()
        Process build = new Process();
        build.StartInfo.WorkingDirectory =  @"dir";
        build.StartInfo.Arguments = "";
        build.StartInfo.FileName = "my.exe";

        build.StartInfo.UseShellExecute = false;
        build.StartInfo.RedirectStandardOutput = true;
        build.StartInfo.RedirectStandardError = true;
        build.StartInfo.CreateNoWindow = true;
        build.ErrorDataReceived += build_ErrorDataReceived;
        build.OutputDataReceived += build_ErrorDataReceived;
        build.EnableRaisingEvents = true;

    // write out info to the display window
    static void build_ErrorDataReceived(object sender, DataReceivedEventArgs e)
        string strMessage = e.Data;
        if (richTextBox != null && !String.Empty(strMessage))
            App.Instance.Dispatcher.BeginInvoke(DispatcherPriority.Send, (ThreadStart)delegate()
                Paragraph para = new Paragraph(new Run(strMessage));
                para.Margin = new Thickness(0);
                para.Background = brushErrorBrush;