Python: get output from a command line which exits with nonzero exit code

Question

I am Using Python 2.7.1 on a Windows Server 2008 R2 x64 box.

I\'m trying to get the output of a command line process which gives a nonzero exit status after

Answer 1

Have you tried stderr=subprocess.STDOUT as mentioned in the python doc page:

To also capture standard error in the result, use stderr=subprocess.STDOUT:

Here is a test code:

import subprocess

try:
    subprocess.check_output('>&2 echo "errrrr"; exit 1', shell=True)
except subprocess.CalledProcessError as e:
    print 'e.output: ', e.output


try:
    subprocess.check_output('>&2 echo "errrrr"; exit 1', shell=True, stderr=subprocess.STDOUT)
except subprocess.CalledProcessError as e:
    print 'e.output: ', e.output

output:

errrrr
e.output:  
e.output:  errrrr

Answer 2

There is an issue here that might be hitting you- http://bugs.python.org/issue9905

Answer 3

You code works fine. Turns out that the process that you are calling is probably outputing to CON. See the following example

import subprocess

def check_output(command):
    process = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True)
    output = process.communicate()
    retcode = process.poll()
    if retcode:
            raise subprocess.CalledProcessError(retcode, command, output=output[0])
    return output 

command = "echo this>CON"

print "subprocess -> " + subprocess.check_output(command, shell=True)
print "native -> " + str(check_output(command))

try:
    subprocess.check_output("python output.py", shell=True)
except subprocess.CalledProcessError, e:
    print "subproces CalledProcessError.output = " + e.output

try:
    check_output("python output.py")
except subprocess.CalledProcessError, e:
    print "native CalledProcessError.output = " + e.output

Output

subprocess -> 
native -> ('', None)
stderr subproces CalledProcessError.output = stdout
native CalledProcessError.output = stderr stdout

Sadly, I do not know how to resolve the issue. Notice that subprocess.check_output results contains only the output from stdout. Your check_output replacement would output both stderr and stdout.

After inspecting subprocess.check_output, it does indeed generate a CalledProcessError with the output containing only stdout.