run linux grep command from python subprocess

Question

I know there are posts already on how to use subprocess in python to run linux commands but I just cant get the syntax correct for this one. please help. This is the command I need to run...

/sbin/ifconfig eth1 | grep "inet addr" | awk -F: '{print $2}' | awk '{print $1}'

Ok this is what I have at the moment that gives a syntax error...

import subprocess
self.ip = subprocess.Popen([/sbin/ifconfig eth1 | grep "inet addr" | awk -F: '{print $2}' | awk '{print $1}'])

Any help greatly appreciated.

Answer 1

This has been gone over many, many times before; but here is a simple pure Python replacement for the inefficient postprocessing.

from subprocess import Popen, PIPE
eth1 = subprocess.Popen(['/sbin/ifconfig', 'eth1'], stdout=PIPE)
out, err = eth1.communicate()
for line in out.split('\n'):
    line = line.lstrip()
    if line.startswith('inet addr:'):
        ip = line.split()[1][5:]

Answer 2

Here's how to construct the pipe in Python (rather than reverting to Shell=True, which is more difficult to secure).

from subprocess import PIPE, Popen

# Do `which` to get correct paths
GREP_PATH = '/usr/bin/grep'
IFCONFIG_PATH = '/usr/bin/ifconfig'
AWK_PATH = '/usr/bin/awk'

awk2 = Popen([AWK_PATH, '{print $1}'], stdin=PIPE)
awk1 = Popen([AWK_PATH, '-F:', '{print $2}'], stdin=PIPE, stdout=awk2.stdin)
grep = Popen([GREP_PATH, 'inet addr'], stdin=PIPE, stdout=awk1.stdin)
ifconfig = Popen([IFCONFIG_PATH, 'eth1'], stdout=grep.stdin)

procs = [ifconfig, grep, awk1, awk2]

for proc in procs:
    print(proc)
    proc.wait()

It'd be better to do the string processing in Python using re. Do this to get the stdout of ifconfig.

from subprocess import check_output

stdout = check_output(['/usr/bin/ifconfig', 'eth1'])
print(stdout)