Python subprocess shell=true custom error message

Question

I am using subprocess in python 3 to use operating system commands (I am on ubuntu 18.04) and I was wondering if there was anyway to make make a custom error message while shell=True

import subprocess
command = str('wrong')
try:
   grepOut = subprocess.check_output(command, shell=True)
except subprocess.CalledProcessError as grepexc:
    print("oops! wrong command")

When i run it I get:

/bin/sh: 1: wrong: not found
oops! wrong command

is there any way to remove the "/bin/sh: 1: wrong: not found" message and just have "oops! wrong command"?

Possible duplicate of [subprocess.check\_output return code](https://stackoverflow.com/questions/23420990/subprocess-check-output-return-code) — Ronan Boiteau, Jan 19 '19 at 23:24

Heath Raftery · Accepted Answer · 2019-01-20T00:12:35.247

1

You can suppress the shell's error message by redirecting stderr, and insert your own by using check_output instead of call:

import subprocess
import os

command = str('wrong command')
devnull = open(os.devnull, 'w')

try:
    output = subprocess.check_output(command, shell=True, stderr=devnull)
except subprocess.CalledProcessError:
    print("oops! wrong command")
    output = ""

print(output)

edited Jan 20 '19 at 00:12

answered Jan 19 '19 at 23:49

Heath Raftery

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Thanks for responding so quickly! Although, I noticed that when command is an actual command such as, command = ' echo Ubuntu!' I get no output – Greer Page Jan 20 '19 at 00:06
I tested that exact scenario and it worked fine for me, but now I see that's only true in the REPL! I've updated the answer to fix the issue. – Heath Raftery Jan 20 '19 at 00:11
Thank you for the help! – Greer Page Jan 20 '19 at 00:42

Python subprocess shell=true custom error message

1 Answers1