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jhwilliams

07-26-2007 12:56 PM

python, os.system() function. howto use python variables?

i would like to do something like this in python:

Code:

myCoolVariable="some_string"

os.system("echo myCoolVariable")

however, the system function views myCoolVariable as a string literal, not as a python variable. What do I do to get around this?

Thank you,
Jameson

pixellany

07-26-2007 01:35 PM

It needs to be one of these forms:

Code:

>>> os.system('echo "asdg"')

asdg

0

>>> os.system("echo 'asdgwere'")

asdgwere

0

The outer quotes define the string to be passed to the shell, and the inner quotes define what gets passed to echo.

jhwilliams

07-26-2007 01:56 PM

That is just printing out the string literals you are passing to echo - i am looking to resolve the python varaible myCoolVariable before the execution of echo in the sysem() call.

For example, I would like:

Code:

$ python

>>>hamburger="potato"

>>>import os

>>>os.system("echo 'hamburger'")

to somehow produce

Code:

potato

0

in this case i could just write "potato" directly, but things get stickier when i want to say

Code:

hamburger=os.system('echo $MY_SHELL_VAR | sed "s/longsed/replacement/g"')

, or something of that flavour

pixellany

07-26-2007 04:14 PM

Bingo!!!

Code:

>>> string="python is cool"

>>> cmd="echo "+string

>>> os.system(cmd)

python is cool

0

>>>

jhwilliams

07-26-2007 05:18 PM

Thanks pixellany!

paddy3118

07-28-2007 01:56 AM

Or do string interpolation:

Code:

bash$ python 

Python 2.4.3 (#1, May 18 2006, 07:40:45) 

[GCC 3.3.3 (cygwin special)] on cygwin

Type "help", "copyright", "credits" or "license" for more information.

>>> from os import system

>>> food = 'spam'

>>> system('echo %(food)s' % locals())

spam

0

>>>

- Paddy.

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