subprocess

In linux, subprocess is implemented with fork + exec

An example

Here is an example to show how a process capture its child’s standard output, see more details in How to capture python subprocess stdout in unittest

import os
import subprocess

from contextlib import contextmanager


@contextmanager
def redirect_stdout(new_out):
    old_stdout = os.dup(1)
    try:
        os.dup2(new_out, 1)
        yield
    finally:
        os.dup2(old_stdout, 1)


def test():
    reader, writer = os.pipe()

    with redirect_stdout(writer):
        subprocess.call(['/bin/echo', 'something happened'], shell=False)

    print(os.read(reader, 1024))