running shell command in python under git-bash not working well

Question

I am using python3 under git-bash environment, and sometimes it does not run shell command well.

#!/usr/bin/env python3


import subprocess as sp

print("hello")

print(sp.getoutput("ls -l"))  # This works.

print(sp.getoutput("date"))   # This hangs and cannot terminate with ctrl-c.

This does not happen when running under normal linux/bash environment.

Then I come across this one: Python not working in the command line of git bash.

I can run using "winpty python ...", however it still cannot terminate even with ctrl-c.

I take back, getoutput("date") hangs but check_output works.

Is the copy of python3 being started a native Windows executable or a cygwin/msys/&c executable? (If it's the latter, the copy of date it starts should be the same as the one bash starts; if it's the former, then not so much). Another important difference is that for a Cygwin python, anywhere it's told to run a shell will start sh; if it's a Windows one, it'll try to start cmd. I would only expect sp.getoutput("ls -l") to ever work with a Windows-built Python; for a Cygwin one or or a more legitimately UNIXy system it needs to be sp.getoutput(["ls", "-l"]) to work at all. — Charles Duffy
– Charles Duffy, Commented Dec 19, 2022 at 17:22
(as a worse-practice alternative, sp.getoutput("ls -l", shell=True) should also work on UNIXy systems, or Python interpreters built for cygwin/msys/etc) — Charles Duffy
– Charles Duffy, Commented Dec 19, 2022 at 17:24
Anyhow -- calling native-Windows date from a more UNIXy Python interpreter, or a more UNIXy date from a native-Windows Python interpreter is liable to cause surprises like those discussed in the other question you linked. — Charles Duffy
– Charles Duffy, Commented Dec 19, 2022 at 17:26

J_H · Accepted Answer · 2022-12-19 05:32:54Z

1

You are needlessly running those commands with a shell.

Prefer this form:

print(sp.check_output(["ls", " -l"]))

print(sp.check_output(["date"]))

answered Dec 19, 2022 at 5:32

J_H

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2 Comments

user180574 Over a year ago

I notice that it could be a git-bash/python problem, as in stackoverflow.com/questions/32597209/…

Charles Duffy Over a year ago

There's no implicit shell=True when there's only a single string passed, so the OP is not using a shell -- shell=True needs to be explicit for that. I suspect that the OP is depending on a Windows-ism (the platform takes argument vector as a shell-like string, not a list). Passing a list tells Python to perform escaping that Microsoft's libc will parse back to the desired argument vector if the program being run doesn't override the parsing.

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