How to spawn a process and capture its STDOUT in .NET? [duplicate]

Answer 1

Here's code that I've verified to work. I use it for spawning MSBuild and listening to its output:

process.StartInfo.UseShellExecute = false;
process.StartInfo.RedirectStandardOutput = true;
process.OutputDataReceived += (sender, args) => Console.WriteLine("received output: {0}", args.Data);
process.Start();
process.BeginOutputReadLine();

Answer 2

It looks like two of your lines are out of order. You start the process before setting up an event handler to capture the output. It's possible the process is just finishing before the event handler is added.

Switch the lines like so.

p.OutputDataReceived += ...
p.Start();        

Answer 3

I needed to capture both stdout and stderr and have it timeout if the process didn't exit when expected. I came up with this:

Process process = new Process();
StringBuilder outputStringBuilder = new StringBuilder();

try
{
process.StartInfo.FileName = exeFileName;
process.StartInfo.WorkingDirectory = args.ExeDirectory;
process.StartInfo.Arguments = args;
process.StartInfo.RedirectStandardError = true;
process.StartInfo.RedirectStandardOutput = true;
process.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
process.StartInfo.CreateNoWindow = true;
process.StartInfo.UseShellExecute = false;
process.EnableRaisingEvents = false;
process.OutputDataReceived += (sender, eventArgs) => outputStringBuilder.AppendLine(eventArgs.Data);
process.ErrorDataReceived += (sender, eventArgs) => outputStringBuilder.AppendLine(eventArgs.Data);
process.Start();
process.BeginOutputReadLine();
process.BeginErrorReadLine();
var processExited = process.WaitForExit(PROCESS_TIMEOUT);

if (processExited == false) // we timed out...
{
    process.Kill();
    throw new Exception("ERROR: Process took too long to finish");
}
else if (process.ExitCode != 0)
{
    var output = outputStringBuilder.ToString();
    var prefixMessage = "";

    throw new Exception("Process exited with non-zero exit code of: " + process.ExitCode + Environment.NewLine + 
    "Output from process: " + outputStringBuilder.ToString());
}
}
finally
{                
process.Close();
}

I am piping the stdout and stderr into the same string, but you could keep it separate if needed. It uses events, so it should handle them as they come (I believe). I have run this successfully, and will be volume testing it soon.