Retrieving the output of subprocess.call() [duplic

Question

This question already has an answer here:

• Store output of subprocess.Popen call in a string 9 answers

How can I get the output of a process run using subprocess.call()?

Passing a StringIO.StringIO object to stdout gives this error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 444, in call
    return Popen(*popenargs, **kwargs).wait()
  File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 588, in __init__
    errread, errwrite) = self._get_handles(stdin, stdout, stderr)
  File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 945, in _get_handles
    c2pwrite = stdout.fileno()
AttributeError: StringIO instance has no attribute 'fileno'
>>> 

Answer 1

In Ipython shell:

In [8]: import subprocess
In [9]: s=subprocess.check_output(["echo", "Hello World!"])
In [10]: s
Out[10]: 'Hello World!\n'

Based on sargue's answer. Credit to sargue.

Answer 2

The following captures stdout and stderr of the process in a single variable. It is Python 2 and 3 compatible:

from subprocess import check_output

command = ["ls", "-l"]
try:
    output = check_output(command, stderr=STDOUT).decode()
    success = True 
except CalledProcessError as e:
    output = e.output.decode()
    success = False

If your command is a string rather than an array, prefix this with:

import shlex
command = shlex.split(command)

Answer 3

If you have Python version >= 2.7, you can use subprocess.check_output which basically does exactly what you want (it returns standard output as string).

Simple example (linux version, see note):

import subprocess

print subprocess.check_output(["ping", "-c", "1", "8.8.8.8"])

Note that the ping command is using linux notation (-c for count). If you try this on Windows remember to change it to -n for same result.

As commented below you can find a more detailed explanation in this other answer.

Answer 4

Output from subprocess.call() should only be redirected to files.

You should use subprocess.Popen() instead. Then you can pass subprocess.PIPE for the stderr, stdout, and/or stdin parameters and read from the pipes by using the communicate() method:

from subprocess import Popen, PIPE

p = Popen(['program', 'arg1'], stdin=PIPE, stdout=PIPE, stderr=PIPE)
output, err = p.communicate(b"input data that is passed to subprocess' stdin")
rc = p.returncode

The reasoning is that the file-like object used by subprocess.call() must have a real file descriptor, and thus implement the fileno() method. Just using any file-like object won't do the trick.

See here for more info.

Answer 5

I recently just figured out how to do this, and here's some example code from a current project of mine:

#Getting the random picture.
#First find all pictures:
import shlex, subprocess
cmd = 'find ../Pictures/ -regex ".*\(JPG\|NEF\|jpg\)" '
#cmd = raw_input("shell:")
args = shlex.split(cmd)
output,error = subprocess.Popen(args,stdout = subprocess.PIPE, stderr= subprocess.PIPE).communicate()
#Another way to get output
#output = subprocess.Popen(args,stdout = subprocess.PIPE).stdout
ber = raw_input("search complete, display results?")
print output
#... and on to the selection process ...

You now have the output of the command stored in the variable "output". "stdout = subprocess.PIPE" tells the class to create a file object named 'stdout' from within Popen. The communicate() method, from what I can tell, just acts as a convenient way to return a tuple of the the output and the errors from the process you've run. Also, the process is run when instantiating Popen.

Answer 6

I have the following solution. It captures the exit code, the stdout, and the stderr too of the executed external command:

import shlex
from subprocess import Popen, PIPE

def get_exitcode_stdout_stderr(cmd):
    """
    Execute the external command and get its exitcode, stdout and stderr.
    """
    args = shlex.split(cmd)

    proc = Popen(args, stdout=PIPE, stderr=PIPE)
    out, err = proc.communicate()
    exitcode = proc.returncode
    #
    return exitcode, out, err

cmd = "..."  # arbitrary external command, e.g. "python mytest.py"
exitcode, out, err = get_exitcode_stdout_stderr(cmd)

I also have a blog post on it here.

Edit: the solution was updated to a newer one that doesn't need to write to temp. files.