Replicate os.system functionality with subprocess in Python?

Question

In my program I want to let the user either run a shell command or execute a binary file. No matter how much I read about subprocess.Popen I can't figure out a way to replicate the os.system() functionality.

I simply want to echo $USER but nothing seems to work.

Turning shell=True..

>>> subprocess.Popen(['echo', '$USER'], shell=True,\
                     stdout=subprocess.PIPE,\
                     stderr=subprocess.PIPE).communicate()
>>> ('\n', '')

Passing current environment vars..

>>> subprocess.Popen(['echo', '$USER'], shell=True,\
                     env=os.environ\
                     stdout=subprocess.PIPE,\
                     stderr=subprocess.PIPE).communicate()
>>> ('\n', '')

So what's the proper way to run a shell command?

------- Edit: requirements ---------

Some people posted answers but maybe I should be more specific. I want to keep both stdout, stderr and return value stored somewhere. All answers seem to give either the one or the other.

or even better, `import getpass` and `getpass.getuser()` for cross-os compatibility. — Łukasz Rogalski, Feb 12 '16 at 12:48
@DanielRoseman because I don't know what commands the user will run so it's easier to just pass all the environments.. — Pithikos, Feb 12 '16 at 12:52
related: [subprocess.call() arguments ignored when using shell=True w/ list](http://stackoverflow.com/q/26417658/4279) — jfs, Feb 13 '16 at 13:34

PYPL · Answer 1 · 2016-02-12T18:10:45.320

1

use call method

subprocess.call('echo $USER',shell=True)

Altarnetivly:

var = subprocess.check_output('echo $USER',shell=True) # .rstrip('\n')
print var

Also with subprocess.Popen()

process = subprocess.Popen("echo $USER",shell=True,stdout=subprocess.PIPE)
print process.communicate()[0],

edited Feb 12 '16 at 18:10

answered Feb 12 '16 at 12:46

PYPL

1,819
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That seems to work but I can't seem to save the output in a variable then.. – Pithikos Feb 12 '16 at 12:53
@Pithikos then go with `check_output` – PYPL Feb 12 '16 at 12:57
thanks, that works. Then though I get no return code. That's why I started with using Popen.. I would prefer to keep all stderr, stdout, return code. – Pithikos Feb 12 '16 at 13:00

score 1 · Accepted Answer · answered Feb 12 '16 at 13:16

Thanks to massiou direction I figured out the answer. The culprit is that when using shell=True you should pass the whole command as a single string!

>>> subprocess.Popen(['echo $USER'], shell=True, \
                     stdout=subprocess.PIPE,\
                     stderr=subprocess.PIPE).communicate()
>>> ('manos\n', '')

The reason is that the first argument in the list will be the one executed as a shell script. The rest arguments are for the shell program itself.

score 0 · Answer 3 · answered Feb 12 '16 at 12:47

0

You can just do something like:

subprocess.call('echo $USER', shell=True)

Also, take a look at Replacing Older Functions with the subprocess Module

answered Feb 12 '16 at 12:47

avamsi

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Replicate os.system functionality with subprocess in Python?

3 Answers3