Redirecting a process' output

Question

Why can't I intercept a process output using Process.StandardOutput when the process is already running? The Process.StartInfo.UseShellExecute and Process.StartInfo.RedirectStandardOutput props are set as they should (false and, respectively true). I keep getting an error: "Process standard output has not been redirected".

robin 0 · Answer

Nevermind time... I don't know how too...

alobiuc · Answer

Thanks for replying but indeed, I am trying to redirect the output of a process already running and doesn't have the RedirectStandardOutput set to true. The almost exact same code you wrote is on my computer for about 2 weeks now. Sorry for the wasted time. Yet, I think there is a way to accomplish what I want since process-spy type programs do exist and they can intercept the output (like I said, Spy++)...but I don't know how.

robin 0 · Answer

If you want to make a redirection of output stream of already running process - I don't know how to do it. From your first post, I've decided that you need to catch output stream of process, that has a RedirectStandartOutput property set to true. If that's it - you could do it. Setting RedirectStandartOutput to true makes process write it's output to it's own stream, and you could get this stream any time by calling process.StandartOutput member. If you'll enumerate running processes and select one you need, you'll get it's standart output stream, if it was redirected and was not closed. This one work, if at least one process with redirected output exists. Process pcs; private void button1_Click(object sender, EventArgs e) { Process[] pcss = Process.GetProcesses(); for (int i = 0; i < pcss.Length; i++) { if (pcss[0].StartInfo.RedirectStandardOutput == true) { pcs = pcss[i]; break; } } } private void button2_Click(object sender, EventArgs e) { string tmpstr = pcs.StandardOutput.ReadLine(); //if stream was closed - Cannot read from closed TextReader error occurs, if process was closed - StandartOut has not been redirected occurs MessageBox.Show(tmpstr); }

alobiuc · Answer

Thanks, but what I want is to redirect the standard output of a process that's already started, not to start it myself. Something like VisualStudio's tool Spy++.

robin 0 · Answer

such error usually occurs if you are trying to get handle to output stream befor you start process. pcs.StartInfo.RedirectStandardOutput = true; StreamReader myStreamReader = pcs.StandardOutput; // error - StandartOut has not been redirected. pcs.Start(); This one is working: Process pcs = new Process(); pcs.StartInfo.FileName = @"c:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\csc.exe"; pcs.StartInfo.UseShellExecute = false; pcs.StartInfo.RedirectStandardOutput = true; pcs.StartInfo.RedirectStandardInput = true; pcs.StartInfo.CreateNoWindow = true; pcs.Start(); string tmpstr = pcs.StandardOutput.ReadToEnd(); MessageBox.Show(tmpstr); pcs.Close();