subprocess.check_output return code

Python 3.5 introduced the subprocess.run() method. The signature looks like:

subprocess.run( args, *, stdin=None, input=None, stdout=None, stderr=None, shell=False, timeout=None, check=False ) 

The returned result is a subprocess.CompletedProcess. In 3.5, you can access the args, returncode, stdout, and stderr from the executed process.

Example:

>>> result = subprocess.run(['ls', '/tmp'], stdout=subprocess.DEVNULL) >>> result.returncode 0 >>> result = subprocess.run(['ls', '/nonexistent'], stderr=subprocess.DEVNULL) >>> result.returncode 2 

is there a way to get a return code without a try/except?

check_output raises an exception if it receives non-zero exit status because it frequently means that a command failed. grep may return non-zero exit status even if there is no error -- you could use .communicate() in this case:

from subprocess import Popen, PIPE pattern, filename = 'test', 'tmp' p = Popen(['grep', pattern, filename], stdin=PIPE, stdout=PIPE, stderr=PIPE, bufsize=-1) output, error = p.communicate() if p.returncode == 0: print('%r is found in %s: %r' % (pattern, filename, output)) elif p.returncode == 1: print('%r is NOT found in %s: %r' % (pattern, filename, output)) else: assert p.returncode > 1 print('error occurred: %r' % (error,)) 

You don't need to call an external command to filter lines, you could do it in pure Python:

with open('tmp') as file: for line in file: if 'test' in line: print line, 

If you don't need the output; you could use subprocess.call():

import os from subprocess import call try: from subprocess import DEVNULL # Python 3 except ImportError: # Python 2 DEVNULL = open(os.devnull, 'r+b', 0) returncode = call(['grep', 'test', 'tmp'], stdin=DEVNULL, stdout=DEVNULL, stderr=DEVNULL) 

Note that since Python 3.5 it is better to use subprocess.run() :

import subprocess grepOut = subprocess.run(['grep', search, 'tmp'], shell=True) ## Only use shell=True if necessary 

This will generate a subprocess.CompletedProcess instance which will be stored at grepOut. Then, and finally answering your question, you can get the return value from subprocess.run() like this:

grepOut.returncode 

which will be equal to 0 if the command was successful, and not equal to 0 if it failed.

Finally, for completeness sake, you could even handle the error by means of a try/except block using the method check_returncode() from subprocess.CompletedProcess class:

try: ## Add argument `capture_output=True` if you want to store the output of the command grepOut = subprocess.run(['grep', search, 'tmp'], shell=True) grepOut.check_returncode() except subprocess.CalledProcessError as err: ## If returncode is non-zero, raise a CalledProcessError and print this message print(f"Oops, something went wrong. Error code: {err.returncode}") 

Hope it is clear enough.

To get both output and return code (without try/except) simply use subprocess.getstatusoutput (Python 3 required)

In Python 2 - use commands module:

import command rc, out = commands.getstatusoutput("ls missing-file") if rc != 0: print "Error occurred: %s" % out 

In Python 3 - use subprocess module:

import subprocess rc, out = subprocess.getstatusoutput("ls missing-file") if rc != 0: print ("Error occurred:", out) 

Error occurred: ls: cannot access missing-file: No such file or directory