Capturing console output from a .NET application (C#)

Question

How do I invoke a console application from my .NET application and capture all the output generated in the console?

(Remember, I don't want to save the information first in a file and then relist as I would love to receive it as live.)

Answer 1

This can be quite easily achieved using the ProcessStartInfo.RedirectStandardOutput property. A full sample is contained in the linked MSDN documentation; the only caveat is that you may have to redirect the standard error stream as well to see all output of your application.

Process compiler = new Process();
compiler.StartInfo.FileName = "csc.exe";
compiler.StartInfo.Arguments = "/r:System.dll /out:sample.exe stdstr.cs";
compiler.StartInfo.UseShellExecute = false;
compiler.StartInfo.RedirectStandardOutput = true;
compiler.Start();    

Console.WriteLine(compiler.StandardOutput.ReadToEnd());

compiler.WaitForExit();

Answer 2

This is bit improvement over accepted answer from @mdb. Specifically, we also capture error output of the process. Additionally, we capture these outputs through events because ReadToEnd() doesn't work if you want to capture both error and regular output. It took me while to make this work because it actually also requires BeginxxxReadLine() calls after Start().

Asynchronous way:

using System.Diagnostics;

Process process = new Process();

void LaunchProcess()
{
    process.EnableRaisingEvents = true;
    process.OutputDataReceived += new System.Diagnostics.DataReceivedEventHandler(process_OutputDataReceived);
    process.ErrorDataReceived += new System.Diagnostics.DataReceivedEventHandler(process_ErrorDataReceived);
    process.Exited += new System.EventHandler(process_Exited);

    process.StartInfo.FileName = "some.exe";
    process.StartInfo.Arguments = "param1 param2";
    process.StartInfo.UseShellExecute = false;
    process.StartInfo.RedirectStandardError = true;
    process.StartInfo.RedirectStandardOutput = true;

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

    //below line is optional if we want a blocking call
    //process.WaitForExit();
}

void process_Exited(object sender, EventArgs e)
{
    Console.WriteLine(string.Format("process exited with code {0}\n", process.ExitCode.ToString()));
}

void process_ErrorDataReceived(object sender, DataReceivedEventArgs e)
{
    Console.WriteLine(e.Data + "\n");
}

void process_OutputDataReceived(object sender, DataReceivedEventArgs e)
{
    Console.WriteLine(e.Data + "\n");
}

Answer 3

Use ProcessStartInfo.RedirectStandardOutput to redirect the output when creating your console process.

Then you can use Process.StandardOutput to read the program output.

The second link has a sample code how to do it.

Answer 4

ConsoleAppLauncher is an open source library made specifically to answer that question. It captures all the output generated in the console and provides simple interface to start and close console application.

The ConsoleOutput event is fired every time when a new line is written by the console to standard/error output. The lines are queued and guaranteed to follow the output order.

Also available as NuGet package.

Sample call to get full console output:

// Run simplest shell command and return its output.
public static string GetWindowsVersion()
{
    return ConsoleApp.Run("cmd", "/c ver").Output.Trim();
}

Sample with live feedback:

// Run ping.exe asynchronously and return roundtrip times back to the caller in a callback
public static void PingUrl(string url, Action<string> replyHandler)
{
    var regex = new Regex("(time=|Average = )(?<time>.*?ms)", RegexOptions.Compiled);
    var app = new ConsoleApp("ping", url);
    app.ConsoleOutput += (o, args) =>
    {
        var match = regex.Match(args.Line);
        if (match.Success)
        {
            var roundtripTime = match.Groups["time"].Value;
            replyHandler(roundtripTime);
        }
    };
    app.Run();
}

Answer 5

I made a reactive version that accepts callbacks for stdOut and StdErr.
onStdOut and onStdErr are called asynchronously,
as soon as data arrives (before the process exits).

public static Int32 RunProcess(String path,
                               String args,
                       Action<String> onStdOut = null,
                       Action<String> onStdErr = null)
    {
        var readStdOut = onStdOut != null;
        var readStdErr = onStdErr != null;

        var process = new Process
        {
            StartInfo =
            {
                FileName = path,
                Arguments = args,
                CreateNoWindow = true,
                UseShellExecute = false,
                RedirectStandardOutput = readStdOut,
                RedirectStandardError = readStdErr,
            }
        };

        process.Start();

        if (readStdOut) Task.Run(() => ReadStream(process.StandardOutput, onStdOut));
        if (readStdErr) Task.Run(() => ReadStream(process.StandardError, onStdErr));

        process.WaitForExit();

        return process.ExitCode;
    }

    private static void ReadStream(TextReader textReader, Action<String> callback)
    {
        while (true)
        {
            var line = textReader.ReadLine();
            if (line == null)
                break;

            callback(line);
        }
    }

Example usage

The following will run executable with args and print

• stdOut in white
• stdErr in red

to the console.

RunProcess(
    executable,
    args,
    s => { Console.ForegroundColor = ConsoleColor.White; Console.WriteLine(s); },
    s => { Console.ForegroundColor = ConsoleColor.Red;   Console.WriteLine(s); } 
);

Answer 6

I've added a number of helper methods to the O2 Platform (Open Source project) which allow you easily script an interaction with another process via the console output and input (see http://code.google.com/p/o2platform/source/browse/trunk/O2_Scripts/APIs/Windows/CmdExe/CmdExeAPI.cs)

Also useful for you might be the API that allows the viewing of the console output of the current process (in an existing control or popup window). See this blog post for more details: http://o2platform.wordpress.com/2011/11/26/api_consoleout-cs-inprocess-capture-of-the-console-output/ (this blog also contains details of how to consume the console output of new processes)

Answer 7

From PythonTR - Python Programcıları Derneği, e-kitap, örnek:

Process p = new Process();   // Create new object
p.StartInfo.UseShellExecute = false;  // Do not use shell
p.StartInfo.RedirectStandardOutput = true;   // Redirect output
p.StartInfo.FileName = "c:\\python26\\python.exe";   // Path of our Python compiler
p.StartInfo.Arguments = "c:\\python26\\Hello_C_Python.py";   // Path of the .py to be executed

Answer 8

Added process.StartInfo.**CreateNoWindow** = true; and timeout.

private static void CaptureConsoleAppOutput(string exeName, string arguments, int timeoutMilliseconds, out int exitCode, out string output)
{
    using (Process process = new Process())
    {
        process.StartInfo.FileName = exeName;
        process.StartInfo.Arguments = arguments;
        process.StartInfo.UseShellExecute = false;
        process.StartInfo.RedirectStandardOutput = true;
        process.StartInfo.CreateNoWindow = true;
        process.Start();

        output = process.StandardOutput.ReadToEnd();

        bool exited = process.WaitForExit(timeoutMilliseconds);
        if (exited)
        {
            exitCode = process.ExitCode;
        }
        else
        {
            exitCode = -1;
        }
    }
}