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

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();

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.

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); } 
);