How to asynchronously read the standard output stream and standard error stream at once

Question

I want to read the ouput of a process in the form as is in a console (standard output is blended with standard error in one stream). Is there a way how to do it?

I w

Answer 1

Similar kind of example, with exception that I'm collecting stdout and error into separate strings using StringBuilder for that purpose.

/// 

/// Executes command
/// 
/// command to be executed
/// output which application produced
/// true - if retain PATH environment variable from executed command
/// true if process exited with code 0
static bool ExecCmd(string cmd, out String output, bool transferEnvVars = false)
{
    ProcessStartInfo processInfo;
    Process process;

    if (transferEnvVars)
        cmd =  cmd + " && echo --VARS-- && set";

    processInfo = new ProcessStartInfo("cmd.exe", "/c " + cmd);
    processInfo.CreateNoWindow = true;
    processInfo.UseShellExecute = false;
    processInfo.RedirectStandardError = true;
    processInfo.RedirectStandardOutput = true;

    process = Process.Start(processInfo);

    // Executing long lasting operation in batch file will hang the process, as it will wait standard output / error pipes to be processed.
    // We process these pipes here asynchronously.
    StringBuilder so = new StringBuilder();
    process.OutputDataReceived += (sender, args) => { so.AppendLine(args.Data); };
    StringBuilder se = new StringBuilder();
    process.ErrorDataReceived += (sender, args) => { se.AppendLine(args.Data); };

    process.BeginOutputReadLine();
    process.BeginErrorReadLine();
    process.WaitForExit();

    output = so.ToString();
    String error = se.ToString();

    if (transferEnvVars)
    {
        Regex r = new Regex("--VARS--(.*)", RegexOptions.Singleline);
        var m = r.Match(output);
        if (m.Success)
        {
            output = r.Replace(output, "");

            foreach ( Match m2 in new Regex("(.*?)=([^\r]*)", RegexOptions.Multiline).Matches(m.Groups[1].ToString()) )
            {
                String key = m2.Groups[1].Value;
                String value = m2.Groups[2].Value;
                Environment.SetEnvironmentVariable(key, value);
            }
        }
    }

    if(error.Length != 0)
        output += error;
    int exitCode = process.ExitCode;

    if (exitCode != 0)
        Console.WriteLine("Error: " + output + "\r\n" + error);

    process.Close();
    return exitCode == 0;
}