rPman

using System;
using System.Threading.Tasks;
using System.IO;
using System.Diagnostics;

namespace ProcessStdoutTaskTest
{
    class MainClass
    {
        static char[] bufOut = new char[5];
        static char[] bufErr = new char[5];
        async static void ReadAsyncStream(StreamReader sr, char[] buf)
        {
            int size;
            while ((size = await sr.ReadBlockAsync(buf, 0, buf.Length)) != 0)
            {
                Console.WriteLine((buf==bufOut?"out":"err")+" '" + new string(buf, 0, size) + "'") ;
            }
        }
        public static void Main(string[] args)
        {
            using (Process process = new Process())
            {
                process.StartInfo.FileName = "/bin/bash";
                process.StartInfo.Arguments = "-c \"printf 'abc';printf 'def' 1>&2;printf 'ghi';printf 'j' 1>&2;\"";
                process.StartInfo.UseShellExecute = false;
                process.StartInfo.RedirectStandardOutput = true;
                process.StartInfo.RedirectStandardError = true;
                process.Start();

                ReadAsyncStream(process.StandardOutput, bufOut);
                ReadAsyncStream(process.StandardError, bufErr);

                Console.Write("Wait to process exit ");
                process.WaitForExit();
                Console.WriteLine("ok");
            }

            Console.WriteLine("Press enter to exit.");
            Console.ReadLine();
        }
    }
}

Wait to process exit ok
Press enter to exit.
out 'abcgh'
out 'i'
err 'defj'