Realtime Console Output Redirection using Process

Question

Hi Guys,

I am using VBOXMANAGE to "export" a guest machine. VBOXManage is a Console application that can control the guest machine's behavior from the host. Since the export command is a long process, it returns process updates like so:

0%...10%...20%...30%...100%

I am writing a C# application that will invoke VBOXManage using Process. Here's my code:

Process VBOXProc = new Process();

VBOXProc.StartInfo.FileName = VBOXMANAGE;
VBOXProc.StartInfo.Arguments = Arguments;
VBOXProc.StartInfo.UseShellExecute = false;
VBOXProc.StartInfo.CreateNoWindow = true;
VBOXProc.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
VBOXProc.StartInfo.RedirectStandardError = true;
VBOXProc.StartInfo.RedirectStandardOutput = true;

VBOXProc.OutputDataReceived += new DataReceivedEventHandler(VBOXProc_OutputDataReceived);
VBOXProc.ErrorDataReceived += new DataReceivedEventHandler(VBOXProc_ErrorDataReceived);

VBOXProc.EnableRaisingEvents = true;

VBOXProc.Start();
VBOXProc.BeginOutputReadLine();
VBOXProc.BeginErrorReadLine();

VBOXProc.WaitForExit();

This is fine, except that the output is being read per LINE. This means that the process updates " 0%...10%...20%...30%...100%" will only show AFTER the actual process is done.

Is there a way to capture the console output in realtime?

Thanks!

Answer 1

You can read directly from the StanadardOutput/Error for the process using all the standard Stream methods, just be sure to set the StartInfo.Redirectxxx to true.

var p = new Process()
p.StartInfo.UseShellExecute = false;  //not sure if this is absolutely required
p.StartInfo.RedirectStandardOuput = true;
....

do
{
  Thread.Sleep(nnn);
  Console.Out.Write(p.StandardOutput.ReadToEnd());
}
while (!p.HasExited);
//catch any leftovers in redirected stdout
Console.Out.Write(p.StandardOutput.ReadToEnd());

The above will echo the output of the child process to your applications Standard Out.

You can read Blocks of a particular size using p.StandardOutput.Read(char[], int, int) or asynchronous reads using p.StadardOutput.BaseStream.BeginRead(...).

All the same methods are available for StandardError.

Sleeping in the loop frees up the processor for other tasks and allows some data to accumulate in the bufffer. If the sleep period is too long and the buffer overflows some output from the executing process will be lost. If the sleep period is too short a lot of CPU cycles are spent reading and empty buffer.