[Tutor] subprocess module: when to _NOT_ use shell=True

[akleider at sonic.net]

Thank you "Eryksun" and "EikeWek" for your responses.  It is this sort of
thing that begins to pull one out of the newbie into the intermediate
category. I'm grateful.
alex

> I've not found anywhere a clear explanation of when not to set shell=True.
> If the command line must be interpreted by the shell then clearly this
> must be set. So the question that comes up is why not set it always?
> In an effort to investigate, I came up with the following script that
> indicates that the shell looks at only the first string in the array if
> the first parameter is an array rather than a string. Switching between
> cmd being a string vs an array and shell being set or not set gives 4
> possibilities.
> Any comments?
>
> #!/usr/bin/env python
>
> # file :  test.py (Python 2.7, NOT Python 3)
> # Running on Linux platform (Ubuntu.)
> print 'Running "tes.py"'
>
> import subprocess
>
> cmd = ["ls", "-l"]
> # cmd = "ls -l"
> p = subprocess.Popen(cmd,
>                     # shell=True,
>                     stdout=subprocess.PIPE,
>                     stderr=subprocess.PIPE)
> (s_out, s_err) = p.communicate()
> print "Std_out returns:\n%s<end>\nStd_err returns:\n%s\n<end>"%\
>           (s_out, s_err, )
>
>
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