subprocess question

[Chris Rebert]

On Sun, Dec 11, 2011 at 8:39 PM,  <jyoung79 at kc.rr.com> wrote:
> Wondering if anyone could shed some light on the subprocess module?  I'll admit I'm not that great at the shell.
>
> If I was wanting to get the size of the trash (on OS X), I could use:
>
>>>> os.system('du -sh ~/.Trash/')
>  11M    /Users/jay/.Trash/
> 0
>
> Which gives me what I want.  However, I've been reading that it's better to use subprocess.  I did a test like so, but is this a good way to do this?
>
>>>> import subprocess
>>>> p = subprocess.Popen(['du', '-sh'], cwd='/Users/jay/.Trash/', stdout=subprocess.PIPE)
>>>> out, err = p.communicate()
>>>> out
> ' 11M\t.\n'

You might prefer to use subprocess.check_output(); it slightly
simplifies your code:
http://docs.python.org/library/subprocess.html#subprocess.check_output

> And another question - why can't I use the tilde as a shortcut to the home directory?

Because ~ is interpolated by the shell and `subprocess` does not use
the shell by default for reasons that include efficiency and security.
You can expand ~ yourself using os.path.expanduser():
http://docs.python.org/library/os.path.html#os.path.expanduser
Alternatively, you can opt to use the shell by passing shell=True as
an argument.

Cheers,
Chris
--
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