Constantly print Subprocess output while process is running

Question

To launch programs from my Python-scripts, I\'m using the following method:

def execute(command):
    process = subprocess.Popen(command, shell=True, stdout=s         


        

Answer 1

In Python >= 3.5 using subprocess.run works for me:

import subprocess

cmd = 'echo foo; sleep 1; echo foo; sleep 2; echo foo'
subprocess.run(cmd, shell=True)

(getting the output during execution also works without shell=True) https://docs.python.org/3/library/subprocess.html#subprocess.run

Answer 2

This works at least in Python3.4

import subprocess

process = subprocess.Popen(cmd_list, stdout=subprocess.PIPE)
for line in process.stdout:
    print(line.decode().strip())

Answer 3

In Python 3.6 I used this:

import subprocess

cmd = "command"
output = subprocess.call(cmd, shell=True)
print(process)

Answer 4

There is actually a really simple way to do this when you just want to print the output:

import subprocess
import sys

def execute(command):
    subprocess.check_call(command, stdout=sys.stdout, stderr=subprocess.STDOUT)

Here we're simply pointing the subprocess to our own stdout, and using existing succeed or exception api.

Answer 5

To answer the original question, the best way IMO is just redirecting subprocess stdout directly to your program's stdout (optionally, the same can be done for stderr, as in example below)

p = Popen(cmd, stdout=sys.stdout, stderr=sys.stderr)
p.communicate()

Answer 6

You can use iter to process lines as soon as the command outputs them: lines = iter(fd.readline, ""). Here's a full example showing a typical use case (thanks to @jfs for helping out):

from __future__ import print_function # Only Python 2.x
import subprocess

def execute(cmd):
    popen = subprocess.Popen(cmd, stdout=subprocess.PIPE, universal_newlines=True)
    for stdout_line in iter(popen.stdout.readline, ""):
        yield stdout_line 
    popen.stdout.close()
    return_code = popen.wait()
    if return_code:
        raise subprocess.CalledProcessError(return_code, cmd)

# Example
for path in execute(["locate", "a"]):
    print(path, end="")