How to get "canonical unix shell" for Python

Question

According to the documentation for the subprocess module, its default shell is /bin/sh, but I have an ingrained, and probably irrational, aversion to hard-coding such constants.

Therefore, I much prefer to refer to some constant defined in subprocess. I have not been able to find any way to interrogate subprocess directly for this constant. The best I've managed is

def _getshpath():
    return subprocess.check_output('which sh', shell=True).strip()

or

def _getshpath():
    return subprocess.check_output('echo "$0"', shell=True).strip()

...both of which look pathetically fragile, since their validity ultimately depend on precisely the specific value I'm trying to determine in the first place. (I.e., if the value of this executable is not "/bin/sh", either definition could easily be nonsensical.)

What's best-practice for getting this path (without hard-coding it as "/bin/sh")?

Thanks!

subprocess itself hardcodes the path as /bin/sh. Maybe you should do the same or just use one of the methods you describe :) — Niklas B.
– Niklas B., Commented Apr 27, 2012 at 22:51
Where is that path hard-coded (/bin/sh)? Is it a member of subprocess? — ncRubert
– ncRubert, Commented Apr 27, 2012 at 23:14
/bin/sh should be the standard POSIX shell, so you can't go wrong with that in a POSIX environment. In any other environment... who knows? — Barton Chittenden
– Barton Chittenden, Commented Apr 27, 2012 at 23:15

John Zwinck · Accepted Answer · 2012-04-27 23:17:38Z

3

Hard-coding it as /bin/sh is perfectly valid. If you look at the documentation for C's popen() you'll find it does this too. /bin/sh is, by construction, the system's standard shell.

answered Apr 27, 2012 at 23:17

John Zwinck

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bmu · Accepted Answer · 2012-04-27 23:27:06Z

1

You could try

>>> import os
>>> shell = os.environ['SHELL']
>>> print shell
'/bin/bash'

You can use this to set the executable argument of subprocess.Popen.

edited Apr 27, 2012 at 23:27

answered Apr 27, 2012 at 23:12

bmu

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