What shell does Python's subprocess use?

Question

This question and answer demonstrates how to use Python's subprocess module to interact with bash from Python.

So if subprocess doesn't use the system's default shell, then what shell does it use to run commands like this:

    import subprocess

    print subprocess.check_output(["ls", "-la"])

on Linux `ls` is normal program - `/bin/ls` - so it can send it directly to system to run program. — furas, Jan 03 '20 at 23:50
so they're system calls to the Kernel using the C Standard Lib? — Sam Malayek, Jan 04 '20 at 00:03
As stated here: https://docs.python.org/3/library/subprocess.html#security-considerations you don't get a shell unless you explicitly ask for one with `shell=True`, and in that case, on Linux, you get `sh`, not `bash`. — PM 2Ring, Jan 04 '20 at 00:06
@SamMalayek Yes. If you don't use `shell=True`, it does its own `fork()` and `exec()`. — Barmar, Jan 04 '20 at 00:11

jmunsch · Accepted Answer · 2020-01-04T00:24:24.387

2

If shell is not passed as a keyword argument it uses fork_exec, or _winapi.CreateProceess

If shell=True:

See:

edited Jan 04 '20 at 00:24

answered Jan 04 '20 at 00:06

jmunsch

1

Since he doesn't use `shell=True`, this answer isn't really relevant. – Barmar Jan 04 '20 at 00:10
Right, thanks, I'm mainly curious about the software components between Python and the program that's executed if it's not a shell. I'm starting to realize that it must be C system calls. – Sam Malayek Jan 04 '20 at 00:10
@SamMalayek np. – jmunsch Jan 04 '20 at 00:25
@SamMalayek, ...I wouldn't really call them "C" system calls -- any C standard-library wrapper like `execlp` eventually goes to an actual syscall, like `execve`, you can invoke without the C library involved at all; hence programs written in languages like Go that don't use libc being able to start other programs. – Charles Duffy Jan 04 '20 at 00:37

1 Answers1