Python os.system without the output

Question

I'm running this:

os.system("/etc/init.d/apache2 restart")

It restarts the webserver, as it should. However, it also outputs a message like so (like it would if I had run the command directly from the terminal)

* Restarting web server apache2                                              ...
waiting                                                             [ OK ]

How can I disable this output?

Glinys

os.system("/etc/init.d/apache2 restart >/dev/null") will discard that output. As Noufal has said, subprocess is preferred. If you're wanting to make a quick adjustment to pre-existing code, though, redirecting to /dev/null might be an attractive option. – Hugues

@kirk: why a comment rather than a answer ? – Corrugation

@mb14: I didn't think it was as "correct" as the recommendations to use subprocess. I thought of it as more of a side note, like "while I'm not exactly suggesting you do this, here's another idea." – Hugues

related: How to hide output of subprocess in Python 2.7 – Rodrigo

this worked for me because i was looking for something which works in python 2 and 3. – Remorseless

You can also see is their is a quiet or silent command line option. This, however, is not garunteed, and the program may still output stderr. – Bibliophage

Answer 1

Avoid os.system() by all means, and use subprocess instead:

with open(os.devnull, 'wb') as devnull:
    subprocess.check_call(['/etc/init.d/apache2', 'restart'], stdout=devnull, stderr=subprocess.STDOUT)

This is the subprocess equivalent of the /etc/init.d/apache2 restart &> /dev/null.

There is subprocess.DEVNULL on Python 3.3+:

#!/usr/bin/env python3
from subprocess import DEVNULL, STDOUT, check_call

check_call(['/etc/init.d/apache2', 'restart'], stdout=DEVNULL, stderr=STDOUT)

Dav

+1 for an actual example that shows how to solve the OPs problem using subprocess. :) – Kamacite

Answer 2

Depending on your OS (and that's why as Noufal said, you should use subprocess instead) you can try something like

 os.system("/etc/init.d/apache restart > /dev/null")

or (to mute also the error)

os.system("/etc/init.d/apache restart > /dev/null 2>&1")

Corrugation

Answer 3

You should use the subprocess module using which you can control the stdout and stderr in a flexible fashion. os.system is deprecated.

The subprocess module allows you to create an object which represents a running external process. You can read it from it's stdout/stderr, write to it's stdin, send it signals, terminate it etc. The main object in the module is Popen. There are a bunch of other convenience methods like call etc. The docs are very comprehensive and include a section on replacing the older functions (including os.system).

Kamacite

Awesome. Thanks for answering. Which function would it be though? The docs confuse me. call? popen? – Glinys

+10 for an incomplete answer! This shows that voting and quality don't go hand in hand :-) . Noufal, you could mention the differences. – Fiord

popen but you should take some time and read through the docs. I imagine you've only skimmed through them. They're quite clear really. – Kamacite

Do you have a source explicitly marking it as deprecated, as opposed to "not preferred"? Guido is on record as being opposed to its removal. I'm not disagreeing with your answer - subprocess is so much nicer! - just clarifying a point. – Hugues

Guido is generally against changing the standard library. The docs for os.system indicate that it's "preferable" to use subprocess. – Kamacite

A A: I think it was fairly complete. All that was needed was a pointer to the right way. I'm surprised at the upvotes though. I've updated it with some more information. – Kamacite

@AA: I think when the answer is to redirect to a doc, a quick answer is a good answer. I think Noufal answer is a good answer then (even though indeed not enough to be accepted). – Corrugation

Answer 4

Here is a system call function I pieced together several years ago and have used in various projects. If you don't want any output from the command at all you can just say out = syscmd(command) and then do nothing with out.

Tested and works in Python 2.7.12 and 3.5.2.

def syscmd(cmd, encoding=''):
    """
    Runs a command on the system, waits for the command to finish, and then
    returns the text output of the command. If the command produces no text
    output, the command's return code will be returned instead.
    """
    p = Popen(cmd, shell=True, stdin=PIPE, stdout=PIPE, stderr=STDOUT,
        close_fds=True)
    p.wait()
    output = p.stdout.read()
    if len(output) > 1:
        if encoding: return output.decode(encoding)
        else: return output
    return p.returncode

Uvea

Answer 5

I was having a similar problem using a Windows machine and found this was the easiest way of fixing my problem

import subprocess
cmd='gdalwarp -overwrite -s_srs EPSG:4283 -t_srs EPSG:28350 -of AAIGrid XXXXX.tif XXXXX.asc'
subprocess.run(cmd,shell=True)

change cmd for whatever you want to run. I iterated this > 1000 times and without the command prompt window appearing, I was able to save a lot of time.

Graduation

Answer 6

When using Python 3.5+ you can also use the newer subprocess.run(...) method and pass the capture_output=True option:

import subprocess
subprocess.run(['/etc/init.d/apache2', 'restart'], capture_output=True)

See the examples in the using-the-subprocess-module section in the docs in case you actually want to capture the output.

Syncrisis