python command substitution for linux commands

Question

I am trying to use command substitution for building a linux command from a python script, but am not able to get the following simple example to work:

LS="/bin/ls -l"
FILENAME="inventory.txt"

cmd = "_LS _FILENAME "
ps= subprocess.Popen(cmd,shell=True,stdout=subprocess.PIPE,stderr=subprocess.STDOUT)
output = ps.communicate()[0]
print output

Thanks!

JB

unutbu · Accepted Answer · 2013-02-10 15:45:50Z

0

Use string substitution:

cmd = '{} {}'.format(LS, FILENAME)

or (in Python2.6):

cmd = '{0} {1}'.format(LS, FILENAME)

import subprocess
import shlex

LS="/bin/ls -l"
FILENAME="inventory.txt"

cmd = '{} {}'.format(LS, FILENAME)    
ps = subprocess.Popen(shlex.split(cmd),
                      stdout = subprocess.PIPE,
                      stderr = subprocess.STDOUT)
output, err = ps.communicate()
print(output)

Or, using the sh module:

import sh
FILENAME = 'inventory.txt'
print(sh.ls('-l', FILENAME, _err_to_out=True))

edited Feb 10, 2013 at 15:45

answered Feb 10, 2013 at 15:27

unutbu

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2 Comments

JamesB Over a year ago

This worked very nicely. For some reason I thought command substitution for python would be under the same title and not Formatting. Thanks!

d33tah Over a year ago

Be wary of security when doing it like this. It's way too easy to add shell injection due to improper quoting.

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