Question

Could you please explain why the shell redirection doesn’t work with System.Diagnostics.Process class? I am trying to redirect the output streams to file with the following snippet:

Process p = new Process();
p.StartInfo = new ProcessStartInfo();
p.StartInfo.FileName = "java.exe";
p.StartInfo.Arguments = @"> c:\Temp\test.log 2>&1";
p.StartInfo.UseShellExecute = true;
p.Start();

The similar code works without problems with Python.
Reading the output streams programmatically doesn’t seem a preferable solution in my case because there will be a bunch of processes launched by my application.

Answer 1

You cannot do the redirection because there is no shell directly involved. You could run a cmd.exe session, but the proper way to do it is using the RedirectStandardOutput/Error properties. There is no problem when having many processes. This is a class I use for this.

    class HandleExecutable {
        private DataReceivedEventHandler outputHandler;

        public DataReceivedEventHandler OutputHandler
        {
            set { outputHandler = value; }
        }
        private DataReceivedEventHandler errorHandler;

        public DataReceivedEventHandler ErrorHandler
        {
            set { errorHandler = value; }
        }

        public void callExecutable(string executable, string args)
        {
            string commandLine = executable;
            string args = args;
            ProcessStartInfo psi = new ProcessStartInfo(commandLine);
            psi.UseShellExecute = false;
            psi.LoadUserProfile = false;
            psi.RedirectStandardOutput = true;
            psi.RedirectStandardError = true;
            psi.WindowStyle = ProcessWindowStyle.Minimized;
            psi.CreateNoWindow = true;
            psi.Arguments = args;
            p = new Process();
            p.StartInfo = psi;
            try
            {
                p.Start();
                p.BeginOutputReadLine();
                p.BeginErrorReadLine();
                if (outputHandler != null) p.OutputDataReceived += outputHandler;
                if (errorHandler != null) p.ErrorDataReceived += errorHandler;
                p.WaitForExit();
                p.Close();
                p.Dispose();
            }
            catch (Exception ex)
            {
                log.Error(ex.Message);
            }
        }
    }

    //On another class
    void p_ErrorDataReceived(object sender, DataReceivedEventArgs e)
    {
        //HANDLE STDERR
        if (e.Data != null && !e.Data.Equals(""))
        {
             if (!e.Data.Contains("Something")) {
             }
        }
    }

    void p_OutputDataReceived(object sender, DataReceivedEventArgs e)
    {
        //HANDLE STDOUT
        if (e.Data != null && !e.Data.Equals(""))
        {
        }
    }

    HandleExecutable he = new HandleExecutable();
    he.OutputHandler = p_OutputDataReceived;
    he.ErrorHandler = p_ErrorDataReceived;
    he.callExecutable(@"C:\java.exe","-cp foo ClassName");