C# Realtime standard output/error capture of a process

Question

I'm developing a C# application and I need to run an external console process (for example a python script) and receive the output data of the script in real-time. The python script is something like this:

import time
while 1:
    print("Hi Foo!")
    time.sleep(.3)

The following C# code prints the python script output on the C# console in real-time:

static void Main(string[] args)
{
    using (Process process = new Process())
    {
        process.StartInfo.FileName = "python.exe";
        process.StartInfo.Arguments = "test.py";
        process.StartInfo.UseShellExecute = false;
        process.Start();
        process.WaitForExit();
    }
}

However, when I try to capture the output data and write them on the console manually, I fail. The recommended solution according to other posts is something like this, but it doesn't work:

static void Main(string[] args)
{
    using (Process process = new Process())
    {
        process.StartInfo.FileName = "python.exe";
        process.StartInfo.Arguments = "test.py";
        process.StartInfo.UseShellExecute = false;
        process.StartInfo.RedirectStandardOutput = true;
        process.EnableRaisingEvents = true;
        process.OutputDataReceived += (s, e) => Console.WriteLine(e.Data);
        process.Start();
        process.BeginOutputReadLine();
        process.WaitForExit();
    }
}

The process.StandardOutput.ReadToEnd() works in blocking mode waiting for the process to exit and returns the whole output all at once. What exactly is the problem with the real-time output capturing and how can I fix it?

First you need to be sure that buffering is not happening on python script side (https://stackoverflow.com/a/31174617), then you can use something like that (https://stackoverflow.com/a/33859530) to read incomplete lines (for me it looks like your script does not emit newline character) from standard output. — user4003407, Sep 12 '18 at 10:49
Possible duplicate of [Disable output buffering](https://stackoverflow.com/questions/107705/disable-output-buffering) — Kirk Larkin, Sep 12 '18 at 11:36

Albert Zabirov · Accepted Answer · 2018-09-12T11:22:43.240

        using (var process = new Process())
        {
            process.StartInfo.FileName = @"python.exe";
            process.StartInfo.Arguments = "-u test.py";
            process.StartInfo.RedirectStandardOutput = true;
            process.StartInfo.UseShellExecute = false;
            process.Start();

            while (!process.StandardOutput.EndOfStream)
            {
                string line = process.StandardOutput.ReadLine();
                Console.WriteLine(line);
                // do something with line
            }
            process.WaitForExit();
            Console.Read();
        }

C# Realtime standard output/error capture of a process

1 Answers1

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