Redirecting standard input of console application

Question

I have a console application which I'm trying to automate by redirecting Standard input stream of the process. In manual mode after opening the application, it waits for user input like below,

I created the process with redirected Standard input stream.The code snippet is as follows,

Process newProcess = new Process();
newProcess.StartInfo.FileName = exeName;
newProcess.StartInfo.Arguments = argsLine;
newProcess.StartInfo.UseShellExecute = false;
newProcess.StartInfo.RedirectStandardOutput = false ;
newProcess.StartInfo.CreateNoWindow = false;
newProcess.StartInfo.RedirectStandardInput = true;
newProcess.Start();

But creating process like this gives an infinite loop shown below,

It's like I'm sending Enter key command continuously to the process input stream. Can anyone point me to what I'm doing wrong here?

Similarly, standard output stream redirection is also not working after making

newProcess.StartInfo.RedirectStandardOutput = true

But I can manage with that.

Does redirection of standard streams work with all console applications or is there any exception?

Answer 1

Here is a class I have written in order to handle that kind of stuff. Feel free to use it. Its purpose is to start a console application and "talk" to it. It has the ability to receive output as well. Good luck.

using System;
using System.Diagnostics;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

public class ConsoleAppManager
{
    private readonly string appName;
    private readonly Process process = new Process();
    private readonly object theLock = new object();
    private SynchronizationContext context;
    private string pendingWriteData;

    public ConsoleAppManager(string appName)
    {
        this.appName = appName;

        this.process.StartInfo.FileName = this.appName;
        this.process.StartInfo.RedirectStandardError = true;
        this.process.StartInfo.StandardErrorEncoding = Encoding.UTF8;

        this.process.StartInfo.RedirectStandardInput = true;
        this.process.StartInfo.RedirectStandardOutput = true;
        this.process.EnableRaisingEvents = true;
        this.process.StartInfo.CreateNoWindow = true;

        this.process.StartInfo.UseShellExecute = false;

        this.process.StartInfo.StandardOutputEncoding = Encoding.UTF8;

        this.process.Exited += this.ProcessOnExited;
    }

    public event EventHandler<string> ErrorTextReceived;
    public event EventHandler ProcessExited;
    public event EventHandler<string> StandartTextReceived;

    public int ExitCode
    {
        get { return this.process.ExitCode; }
    }

    public bool Running
    {
        get; private set;
    }

    public void ExecuteAsync(params string[] args)
    {
        if (this.Running)
        {
            throw new InvalidOperationException(
                "Process is still Running. Please wait for the process to complete.");
        }

        string arguments = string.Join(" ", args);

        this.process.StartInfo.Arguments = arguments;

        this.context = SynchronizationContext.Current;

        this.process.Start();
        this.Running = true;

        new Task(this.ReadOutputAsync).Start();
        new Task(this.WriteInputTask).Start();
        new Task(this.ReadOutputErrorAsync).Start();
    }

    public void Write(string data)
    {
        if (data == null)
        {
            return;
        }

        lock (this.theLock)
        {
            this.pendingWriteData = data;
        }
    }

    public void WriteLine(string data)
    {
        this.Write(data + Environment.NewLine);
    }

    protected virtual void OnErrorTextReceived(string e)
    {
        EventHandler<string> handler = this.ErrorTextReceived;

        if (handler != null)
        {
            if (this.context != null)
            {
                this.context.Post(delegate { handler(this, e); }, null);
            }
            else
            {
                handler(this, e);
            }
        }
    }

    protected virtual void OnProcessExited()
    {
        EventHandler handler = this.ProcessExited;
        if (handler != null)
        {
            handler(this, EventArgs.Empty);
        }
    }

    protected virtual void OnStandartTextReceived(string e)
    {
        EventHandler<string> handler = this.StandartTextReceived;

        if (handler != null)
        {
            if (this.context != null)
            {
                this.context.Post(delegate { handler(this, e); }, null);
            }
            else
            {
                handler(this, e);
            }
        }
    }

    private void ProcessOnExited(object sender, EventArgs eventArgs)
    {
        this.OnProcessExited();
    }

    private async void ReadOutputAsync()
    {
        var standart = new StringBuilder();
        var buff = new char[1024];
        int length;

        while (this.process.HasExited == false)
        {
            standart.Clear();

            length = await this.process.StandardOutput.ReadAsync(buff, 0, buff.Length);
            standart.Append(buff.SubArray(0, length));
            this.OnStandartTextReceived(standart.ToString());
            Thread.Sleep(1);
        }

        this.Running = false;
    }

    private async void ReadOutputErrorAsync()
    {
        var sb = new StringBuilder();

        do
        {
            sb.Clear();
            var buff = new char[1024];
            int length = await this.process.StandardError.ReadAsync(buff, 0, buff.Length);
            sb.Append(buff.SubArray(0, length));
            this.OnErrorTextReceived(sb.ToString());
            Thread.Sleep(1);
        }
        while (this.process.HasExited == false);
    }

    private async void WriteInputTask()
    {
        while (this.process.HasExited == false)
        {
            Thread.Sleep(1);

            if (this.pendingWriteData != null)
            {
                await this.process.StandardInput.WriteLineAsync(this.pendingWriteData);
                await this.process.StandardInput.FlushAsync();

                lock (this.theLock)
                {
                    this.pendingWriteData = null;
                }
            }
        }
    }
}

Answer 2

Following the previous answer, I'll just add the extension method of SubArray, just in case add this class to your code where it's not nested inside any class ( the code didn't look readable in a comment, so I added it here )

public static class CharArrayExtensions
{
    public static char[] SubArray(this char[] input,int startIndex, int length)
    {
        List<char> result= new List<char>();
        for (int i = startIndex; i < length; i++)
        {
            result.Add(input[i]);
        }

        return result.ToArray();
    }
}

Answer 3

Thank you for the ConsoleAppManager, it works well but I have to mention that the same effect for capturing output and error messages could be achieved using events found in the Process class:OutputDataReceived and ErrorDataReceived and call BeginOutputReadLine() and BeginErrorReadLine() after starting the process.

Also that WriteInputTask() is killing the CPU, might want to use some sort of ResetEvent between the while loop and setting of pendingWriteData or send the input directly to the process.