Save result from system command to a variable using subprocess

Question

I would like to get the first interface that is up on a linux machine. I am using subproces and I have the following piece of code :

def get_eth_iface():
    awk_sort = subprocess.Popen( ["-c", "ifconfig | cut -d ' ' -f 1 | grep eth | head -n 1" ], stdin= subprocess.PIPE, shell=True )
    awk_sort.wait()
    output = awk_sort.communicate()[0]

But with this result will be printed to the console and won't be saved to the variable. How can I redirect this to the variable ?

Holger · Accepted Answer · 2013-01-21 12:22:08Z

1

Redirect the stdout to subprocess.PIPE. Following works for me.

import subprocess
def get_eth_iface():
    awk_sort = subprocess.Popen( ["dir" ], stdin= subprocess.PIPE, stdout= subprocess.PIPE)
    awk_sort.wait()
    output = awk_sort.communicate()[0]
    print output.rstrip()
get_eth_iface()

edited Jan 21, 2013 at 12:22

answered Jan 21, 2013 at 11:51

Holger

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2 Comments

Patryk Over a year ago

Ok, thanks that works good BUT : I have to do that output = awk_sort.communicate()[0]to get the actual interface name + I get the interface name with new line sign. How can I get rid of that ?

Holger Over a year ago

Just use the rstrip method on strings.

Anton Kovalenko · Accepted Answer · 2013-01-21 11:47:06Z

1

http://docs.python.org/2/library/subprocess.html:

Similarly, to get anything other than None in the result tuple, you need to give stdout=PIPE and/or stderr=PIPE too.

Sounds like a good advice. Add stdout=subprocess.PIPE and see what happens.

answered Jan 21, 2013 at 11:47

Anton Kovalenko

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