subprocess - Python os.system without the output

28
votes

I'm running this:

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

It restarts the webserver, as it should, and like it would if I had run the command directly from the terminal, it outputs this:

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

However, I don't want it to actually output it in my app. How can I disable it? Thanks!

4
pythonsubprocessos.system
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. - Kirk Strauser
@kirk: why a comment rather than a answer ? - mb14
@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." - Kirk Strauser
related: How to hide output of subprocess in Python 2.7 - jfs
this worked for me because i was looking for something which works in python 2 and 3. - ChathuraG

4 Answers

45
votes

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)
28
votes

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")
24
votes

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).

1
votes

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