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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.

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    Why don't you just use os.environ['USER']? Commented Feb 12, 2016 at 12:47
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    or even better, import getpass and getpass.getuser() for cross-os compatibility. Commented Feb 12, 2016 at 12:48
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    @DanielRoseman because I don't know what commands the user will run so it's easier to just pass all the environments.. Commented Feb 12, 2016 at 12:52
  • related: subprocess.call() arguments ignored when using shell=True w/ list Commented Feb 13, 2016 at 13:34

3 Answers 3

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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.

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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],
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That seems to work but I can't seem to save the output in a variable then..
@Pithikos then go with check_output
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.
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You can just do something like:

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

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

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