What is the return value of subprocess.call()?

Question

I am not sure what the return value of subprocess.call() means.

• Can I safely assume a zero value will always mean that the command executed successfully?

• Is the return value equivalent to the exit staus of a shell command?

For example, will the following piece of code work for virtually any command on Linux?

 cmd = "foo.txt > bar.txt"
 ret = subprocess.call(cmd, shell=True)
 if ret != 0:
     if ret < 0:
         print "Killed by signal", -ret
     else:
         print "Command failed with return code", ret
 else:
     print "SUCCESS!!"

Please enlighten me :-)

Answer 1

Yes, Subprocess.call returns "actual process return code".

You can check official documentation of Subprocess.call and Subprocess.Popen.returncode

Answer 2

It is the return code, but keep in mind it's up to the author of the subprocess what the return code means. There is a strong culture of 0 meaning success, but there's nothing enforcing it.

Answer 3

You are at the mercy of the commands that you call. Consider this:

test.py

#!/usr/bin/env python
success=False
if not success:
    exit()

Then running your code (with cmd='test.py') will result in SUCCESS!!

merely because test.py does not conform to the convention of returning a non-zero value when it is not successful.