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Date: Thu, 29 May 2014 15:10:24 +1000
From: Cameron Simpson <cs@zip.com.au>
To: python-list@python.org
Subject: Re: passing Python assignment value to shell
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On 28May2014 21:48, Satish Muthali <satish.muthali@gmail.com> wrote:
>This is what I went about doing:
>
>    reecalc = [s.split() for s in os.Popen("free -ht").read().splitlines()]

I think you dropped an "f" in your cut/paste. Try to be precise.

>    freecalc_total = freecalc[4]
>    freecalc_total = freecalc_total[3]
>    freecalc_total = freecalc_total.translate(None, 'M )

This is syntacticly invalid. Did this really come from working code?
Also, .translate does not accept None as its first argument.

>   tmp = "%s" % freecalc_total

If freecalc_total is a string (as it seems from the above) then this line does 
nothing.

If freecalc_total were a number, it would probably be better to use "%d" 
instead of "%s"; %d will emit an error if freecalc_total is not a number, a 
useful sanity check.

>  command = "stressapptest -M %s -s 20" % tmp
>  p = subprocess.Popen(command, shell=True,  stdout=subprocess.PIPE, stderr=
>subprocess.PIPE).communicate()[0]
>
>Please let me know if this is the optimal method to achieve in order to pass
>the assignment value to shell. I am open to suggestions or a better way of
>implementation/logic.

It is better to avoid shell=True unless you really need to run a shell command 
(shell syntax or control structures, etc). This is because by plonking "%s" in 
the middle of your shell string, you leave yourself open to "injection" 
accidents (or attacks, of you can be tricked in the values you substitute).

Since you are running a command with known arguments and no shell syntax, you 
do not need the shell. So just construct the arguments directly:

   [ "stressapptest", "-M", str(freecalc_total), "-s", "20" ]

and set shell=False.

Cheers,
Cameron Simpson <cs@zip.com.au>