returncode in Python subprocess module always returns 0 [duplicate]

Question

I am triggering a shell script using a Python script and get its exit code for further processing. I am using the subprocess module. But when I try to capture the return code for further processing it is always 0 even if the script failed.

Below is my Python code:

import subprocess
import os
    
    
dpath = "/home/admin/temp"
password = "password"
password_bytes = bytes(password + '\n', encoding='utf-8')
proc = subprocess.Popen(['sudo', '-S', 'sh', os.path.join(dpath,'test1.sh'),'hello'], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = proc.communicate(input=password_bytes)
    
print(proc.returncode)
print(out)
if proc.returncode == 0:
    print("success")
else:
    print("fail")

Below is my shell script

cat file.txt #File.txt does not exist
echo $?

Below is my python output

0
b'1\n'
success

You can see print(out) gives exit code 1 but proc.returncode gives 0.

jthulhu · Accepted Answer · 2022-02-23 08:30:55Z

1

The return code is 0 because you have added an echo statement, which does not fail. Try simply having cat file where file does not exist, without the echo statement.

answered Feb 23, 2022 at 8:30

jthulhu

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1 Comment

tripleee Over a year ago

To point out explicitly why that is, the exit code of a script is the exit code of the last command in the script; so, here, echo.

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