Read a log file while a subprocess is running

Question

I have a process that outputs logs to a file, and I'm trying to make a python script to run that process and output only the log that it generates into that log file.

What I wrote below seems to do what I want except for one big issue: it never exists the while loop. I've tried a few other alternatives with no luck.

Any help here would be really appreciated! I guess it's worth noting I could also use node script instead...

import subprocess
import sh

process = subprocess.Popen(cmd)

log_tail = sh.tail("-f", log_file, _iter=True)

while process.returncode is None:
    sys.stdout.write(log_tail.next())
    sys.stdout.flush()
    process.poll()

Answer 1

The tail -f command is intended to run until explicitly interrupted, which is why the loop is never exited. You could try this:

import subprocess

p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
stdout, stderr = p.communicate()

which will wait until the cmd terminates and return the contents of its output streams in stdout and stderr .