Sending commands to cmd prompt in C#

Question

For one of my implementations I am working on a tool that is supposed to send/retrieve commands/results to/from the cmd window. Everything works fine but the Use case below fails to do anything. It seems as if my application is waiting for something (instead of displaying the result)

From my tool I navigate to the python folder . From the python folder I try to launch python.exe but at this point, my editor does not do anything. it simply keeps on waiting.

For your kind consideration I am also linking the video here. It would be easier for you guys to understand what I am trying to say.

View the Video here (on youtube)

I am also attaching the code that I currently have.

            ProcessStartInfo info = new ProcessStartInfo("cmd.exe");

            string argument = null;
            if (!string.IsNullOrEmpty(startingDirectory) && System.IO.Directory.Exists(startingDirectory))
            {
               argument += @"cd\";
            }
            else
            {
                argument += "\"";
            }
            info.Arguments = argument;
            info.CreateNoWindow = true;
            info.RedirectStandardError = true;
            info.RedirectStandardInput = true;
            info.RedirectStandardOutput = true;
            info.UseShellExecute = false;
             this.shellProcess = System.Diagnostics.Process.Start(info);
            this.shellProcess.EnableRaisingEvents = true;
            //this.InputStream.AutoFlush = true;
            this.shellProcess.Exited += new EventHandler(ProcessExited);
            this.ErrorBeginRead();
            this.OutputBeginRead();

 private void OutputBeginRead()
    {
        this.shellProcess.StandardOutput.BaseStream.BeginRead(outputBuffer, 0, outputBuffer.Length, new AsyncCallback(this.OnOutputInput), this.shellProcess);
    }

        private void ErrorBeginRead()
    {
        this.shellProcess.StandardError.BaseStream.BeginRead(errorBuffer, 0, errorBuffer.Length, new AsyncCallback(this.OnErrorInput), this.shellProcess);
    }

Thank you !

EDIT: Launching python is just an example. I need to use the same method for other normal cmd line commands as well.It would be nice, if somebody can point what i am doing wrong with the code that I have or what I must do , in order to achieve the intended functionality.

EDIT 2 : The normal cmd commands are working perfectly. The command line tools like python,perl are not working .

Edit 3 : So I managed to do move a wee bit forward following Jamie's suggestions. The ui is not "hanging" anymore. but when i access the python interpreter , the interpreter's output is still not visible in my tool. Any suggestions why that might be happening ?

Answer 1

You cannot send commands to a shell this way. The string in info.Arguments is the arguments provided to the program on the command line. If you want the cmd.exe shell to execute a series of command and then quit you will have to provide the /c argument. If you have multiple commands that you want it to perform you will either have to put the commands in a batch file and execute that or enclose them in quotes and separate them with &&, i.e. info.Arguments = @"/c ""cd \ && dir""";. Your other issue with never returning is that cmd.exe opens in interactive mode by default when it is executed without any, or proper, arguments. The /c option tells cmd.exe to execute the relevant commands and then quit.

Additionally, interpreters like python and perl sometimes have weird behaviors when launched directly from ProcessStartInfo. If info.Arguments = @"""MyPerlProgram.pl"""; with perl.exe doesn't work, you may find it necessary to launch them inside cmd.exe to get normal behavior out of them, i.e. info.Arguments = @"/c ""perl.exe ""MyPerlProgram.pl""""";.

See Cmd and ProcessStartInfo.Arguments Property.

To answer your Edit 3 problem, you're probably not correctly hooking into the outputs. Instead of trying to hook the StreamReader's BaseStream, hook the OutputDataReceived event with this.shellProcess.OutputDataReceived += ProcessOutputHandler; before you call Start where ProcessOutputHandler has a signature like public static void ProcessOutputHandler(object sendingProcess, DataReceivedEventArgs outLine). Immediately after calling Start, call this.shellProcess.BeginOutputReadLine();. The process is similar for the error ouput as well. See Process.BeginOutputReadLine Method and Process.BeginErrorReadLine Method for more details.

If you still have a problem, what do you get if you just try process.StartInfo.Arguments = @"/c ""python.exe -c ""import sys; print 'Test.';""""";?

Also, the code below demonstrates most of the necessary concepts for shell communication:

public static void Main()
{
    using (Process process = new Process())
    {
        process.StartInfo.UseShellExecute = false;
        process.StartInfo.RedirectStandardOutput = true;
        process.StartInfo.RedirectStandardError = true;
        process.StartInfo.WorkingDirectory = @"C:\";
        process.StartInfo.FileName = Path.Combine(Environment.SystemDirectory, "cmd.exe");

        // Redirects the standard input so that commands can be sent to the shell.
        process.StartInfo.RedirectStandardInput = true;
        // Runs the specified command and exits the shell immediately.
        //process.StartInfo.Arguments = @"/c ""dir""";

        process.OutputDataReceived += ProcessOutputDataHandler;
        process.ErrorDataReceived += ProcessErrorDataHandler;

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

        // Send a directory command and an exit command to the shell
        process.StandardInput.WriteLine("dir");
        process.StandardInput.WriteLine("exit");

        process.WaitForExit();
    }
}

public static void ProcessOutputDataHandler(object sendingProcess, DataReceivedEventArgs outLine)
{
    Console.WriteLine(outLine.Data);
}

public static void ProcessErrorDataHandler(object sendingProcess, DataReceivedEventArgs outLine)
{
    Console.WriteLine(outLine.Data);
}

You may have threading issues causing your problems. I've done some further work with this and was able to get a textbox on a form to update with the following code:

using System;
using System.Diagnostics;
using System.IO;
using System.Timers;

namespace DummyFormsApplication
{
    class ProcessLauncher : IDisposable
    {
        private Form1 form;
        private Process process;
        private bool running;

        public bool InteractiveMode
        {
            get;
            private set;
        }

        public ProcessLauncher(Form1 form)
        {
            this.form = form;

            process = new Process();
            process.StartInfo.UseShellExecute = false;
            process.StartInfo.RedirectStandardOutput = true;
            process.StartInfo.RedirectStandardError = true;
            process.StartInfo.WorkingDirectory = @"C:\";
            process.StartInfo.FileName = Path.Combine(Environment.SystemDirectory, "cmd.exe");

            // Redirects the standard input so that commands can be sent to the shell.
            process.StartInfo.RedirectStandardInput = true;

            process.OutputDataReceived +=new DataReceivedEventHandler(process_OutputDataReceived);
            process.ErrorDataReceived += new DataReceivedEventHandler(process_ErrorDataReceived);
            process.Exited += new EventHandler(process_Exited);
        }

        public void Start()
        {
            if (running == false)
            {
                running = true;
                InteractiveMode = true;

                // Runs the specified command and exits the shell immediately upon completion.
                process.StartInfo.Arguments = @"/c ""C:\python27\python.exe -i""";

                process.Start();

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

        public void Start(string scriptFileName)
        {
            if (running == false)
            {
                running = true;
                InteractiveMode = false;

                // Runs the specified command and exits the shell immediately upon completion.
                process.StartInfo.Arguments = string.Format(@"/c ""C:\python27\python.exe ""{0}""""", scriptFileName);
            }
        }

        public void Abort()
        {
            process.Kill();
        }

        public void SendInput(string input)
        {
            process.StandardInput.Write(input);
            process.StandardInput.Flush();
        }

        private void process_OutputDataReceived(object sendingProcess, DataReceivedEventArgs outLine)
        {
            if (outLine.Data != null)
            {
                form.Invoke(form.appendConsoleTextDelegate, new object[] { outLine.Data });
            }
        }

        private void process_ErrorDataReceived(object sendingProcess, DataReceivedEventArgs outLine)
        {
            if (outLine.Data != null)
            {
                form.Invoke(form.appendConsoleTextDelegate, new object[] { outLine.Data });
            }
        }

        private void process_Exited(object sender, EventArgs e)
        {
            running = false;
        }

        public void Dispose()
        {
            if (process != null)
            {
                process.Dispose();
            }
        }
    }
}

I created a form and added a textbox and the following code in the form:

    public delegate void AppendConsoleText(string text);
    public AppendConsoleText appendConsoleTextDelegate;

    private void Form1_Load(object sender, EventArgs e)
    {
        appendConsoleTextDelegate = new AppendConsoleText(textBox1_AppendConsoleText);
        using (ProcessLauncher launcher = new ProcessLauncher(this))
        {
            launcher.Start();

            launcher.SendInput("import sys;\n");
            launcher.SendInput("print \"Test.\";\n");
            launcher.SendInput("exit()\n");
        }
    }

    private void textBox1_AppendConsoleText(string text)
    {
        textBox1.AppendText(string.Format("{0}\r\n", text));
    }

One thing to note is that if the Form1_Load event doesn't complete, Invoke will hang until it does. If you have long-running code in an event you'll either need to invoke asynchronously using BeginInvoke, or periodically call DoEvents in your long-running code.

EDIT

Per your comment, I've modified the code to work with interactive submissions. There is, however, a problem. The python prompt (>>>) is provided on the StandardError output and it does not echo the StandardInput. It also does not terminate the line. This makes detecting a prompt difficult and causes some out of order output of the prompt characters due to the process_ErrorDataReceived not firing until either the process ends or a line end is seen.