Store output of subprocess.Popen call in a string

Question

I\'m trying to make a system call in Python and store the output to a string that I can manipulate in the Python program.

#!/usr/bin/python
import subprocess         


        

Answer 1

Assuming that pwd is just an example, this is how you can do it:

import subprocess

p = subprocess.Popen("pwd", stdout=subprocess.PIPE)
result = p.communicate()[0]
print result

See the subprocess documentation for another example and more information.

Answer 2

In Python 2.7 or Python 3

Instead of making a Popen object directly, you can use the subprocess.check_output() function to store output of a command in a string:

from subprocess import check_output
out = check_output(["ntpq", "-p"])

In Python 2.4-2.6

Use the communicate method.

import subprocess
p = subprocess.Popen(["ntpq", "-p"], stdout=subprocess.PIPE)
out, err = p.communicate()

out is what you want.

Important note about the other answers

Note how I passed in the command. The "ntpq -p" example brings up another matter. Since Popen does not invoke the shell, you would use a list of the command and options—["ntpq", "-p"].

Answer 3

The accepted answer is still good, just a few remarks on newer features. Since python 3.6, you can handle encoding directly in check_output, see documentation. This returns a string object now:

import subprocess 
out = subprocess.check_output(["ls", "-l"], encoding="utf-8")

In python 3.7, a parameter capture_output was added to subprocess.run(), which does some of the Popen/PIPE handling for us, see the python docs :

import subprocess 
p2 = subprocess.run(["ls", "-l"], capture_output=True, encoding="utf-8")
p2.stdout

Answer 4

For python 3.5 I put up function based on previous answer. Log may be removed, thought it's nice to have

import shlex
from subprocess import check_output, CalledProcessError, STDOUT


def cmdline(command):
    log("cmdline:{}".format(command))
    cmdArr = shlex.split(command)
    try:
        output = check_output(cmdArr,  stderr=STDOUT).decode()
        log("Success:{}".format(output))
    except (CalledProcessError) as e:
        output = e.output.decode()
        log("Fail:{}".format(output))
    except (Exception) as e:
        output = str(e);
        log("Fail:{}".format(e))
    return str(output)


def log(msg):
    msg = str(msg)
    d_date = datetime.datetime.now()
    now = str(d_date.strftime("%Y-%m-%d %H:%M:%S"))
    print(now + " " + msg)
    if ("LOG_FILE" in globals()):
        with open(LOG_FILE, "a") as myfile:
            myfile.write(now + " " + msg + "\n")

Answer 5

This was perfect for me. You will get the return code, stdout and stderr in a tuple.

from subprocess import Popen, PIPE

def console(cmd):
    p = Popen(cmd, shell=True, stdout=PIPE)
    out, err = p.communicate()
    return (p.returncode, out, err)

For Example:

result = console('ls -l')
print 'returncode: %s' % result[0]
print 'output: %s' % result[1]
print 'error: %s' % result[2]

Answer 6

subprocess.Popen: http://docs.python.org/2/library/subprocess.html#subprocess.Popen

import subprocess

command = "ntpq -p"  # the shell command
process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=None, shell=True)

#Launch the shell command:
output = process.communicate()

print output[0]

In the Popen constructor, if shell is True, you should pass the command as a string rather than as a sequence. Otherwise, just split the command into a list:

command = ["ntpq", "-p"]  # the shell command
process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=None)

If you need to read also the standard error, into the Popen initialization, you can set stderr to subprocess.PIPE or to subprocess.STDOUT:

import subprocess

command = "ntpq -p"  # the shell command
process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)

#Launch the shell command:
output, error = process.communicate()