Return value of x = os.system(..)

Question

When I type os.system("whoami") in Python, as root, it returns root, but when I try to assign it to a variable x = os.system("whoami") it set's the value of x to 0. Why ? (:

Solution 1

os.system() returns the (encoded) process exit value. 0 means success:

On Unix, the return value is the exit status of the process encoded in the format specified for wait(). Note that POSIX does not specify the meaning of the return value of the C system() function, so the return value of the Python function is system-dependent.

The output you see is written to stdout, so your console or terminal, and not returned to the Python caller.

If you wanted to capture stdout, use subprocess.check_output() instead:

x = subprocess.check_output(['whoami'])

Solution 2

os.system('command') returns a 16 bit number, which first 8 bits from left(lsb) talks about signal used by os to close the command, Next 8 bits talks about return code of command.

Refer my answer for more detail in What is the return value of os.system() in Python?