Assign output of os.system to a variable and prevent it from being displayed on the screen

I want to assign the output of a command I run using os.system to a variable and prevent it from being output to the screen. But, in the below code ,the output is sent to the screen and the value printed for var is 0, which I guess signifies whether the command ran successfully or not. Is there any way to assign the command output to the variable and also stop it from being displayed on the screen?

var = os.system("cat /etc/services")
print var #Prints 0

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

From “Equivalent of Bash Backticks in Python“, which I asked a long time ago, what you may want to use is popen:

os.popen('cat /etc/services').read()

From the docs for Python 3.6,

This is implemented using subprocess.Popen; see that class’s
documentation for more powerful ways to manage and communicate with
subprocesses.

Here’s the corresponding code for subprocess:

import subprocess

proc = subprocess.Popen(["cat", "/etc/services"], stdout=subprocess.PIPE, shell=True)
(out, err) = proc.communicate()
print "program output:", out

Method 2

You might also want to look at the subprocess module, which was built to replace the whole family of Python popen-type calls.

import subprocess
output = subprocess.check_output("cat /etc/services", shell=True)

The advantage it has is that there is a ton of flexibility with how you invoke commands, where the standard in/out/error streams are connected, etc.

Method 3

The commands module is a reasonably high-level way to do this:

import commands
status, output = commands.getstatusoutput("cat /etc/services")

status is 0, output is the contents of /etc/services.

Method 4

For python 3.5+ it is recommended that you use the run function from the subprocess module. This returns a CompletedProcess object, from which you can easily obtain the output as well as return code. Since you are only interested in the output, you can write a utility wrapper like this.

from subprocess import PIPE, run

def out(command):
    result = run(command, stdout=PIPE, stderr=PIPE, universal_newlines=True, shell=True)
    return result.stdout

my_output = out("echo hello world")
# Or
my_output = out(["echo", "hello world"])

Method 5

I know this has already been answered, but I wanted to share a potentially better looking way to call Popen via the use of from x import x and functions:

from subprocess import PIPE, Popen


def cmdline(command):
    process = Popen(
        args=command,
        stdout=PIPE,
        shell=True
    )
    return process.communicate()[0]

print cmdline("cat /etc/services")
print cmdline('ls')
print cmdline('rpm -qa | grep "php"')
print cmdline('nslookup google.com')

Method 6

i do it with os.system temp file:

import tempfile,os
def readcmd(cmd):
    ftmp = tempfile.NamedTemporaryFile(suffix='.out', prefix='tmp', delete=False)
    fpath = ftmp.name
    if os.name=="nt":
        fpath = fpath.replace("/","\") # forwin
    ftmp.close()
    os.system(cmd + " > " + fpath)
    data = ""
    with open(fpath, 'r') as file:
        data = file.read()
        file.close()
    os.remove(fpath)
    return data

Method 7

Python 2.6 and 3 specifically say to avoid using PIPE for stdout and stderr.

The correct way is

import subprocess

# must create a file object to store the output. Here we are getting
# the ssid we are connected to
outfile = open('/tmp/ssid', 'w');
status = subprocess.Popen(["iwgetid"], bufsize=0, stdout=outfile)
outfile.close()

# now operate on the file

Method 8

from os import system, remove
from uuid import uuid4

def bash_(shell_command: str) -> tuple:
    """

    :param shell_command: your shell command
    :return: ( 1 | 0, stdout)
    """

    logfile: str = '/tmp/%s' % uuid4().hex
    err: int = system('%s &> %s' % (shell_command, logfile))
    out: str = open(logfile, 'r').read()
    remove(logfile)
    return err, out

# Example: 
print(bash_('cat /usr/bin/vi | wc -l'))
>>> (0, '3296n')```

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0