awk from Python: wrong subprocess arguments?

Question

I need to run the following (working) command in Python:

ip route list dev eth0 | awk ' /^default/ {print $3}'

Using subprocess, I would have to do the following:

first = "ip route list dev eth0"
second = "awk ' /^default/ {print $3}'"
p1 = subprocess.Popen(first.split(), stdout=subprocess.PIPE)
p2 = subprocess.Popen(second.split(), stdin=p1.stdout, stdout=subprocess.PIPE)
p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
output = p2.communicate()[0]

Something went wrong with p2. I get:

>>> awk: cmd. line:1: '
awk: cmd. line:1: ^ invalid char ''' in expression

What should I do? On a terminal it works perfectly.

ecatmur · Accepted Answer · 2013-03-14 16:06:13Z

16

split splits on any whitespace, including that inside single-quoted arguments. If you really have to, use shlex.split:

import shlex
p2 = subprocess.Popen(shlex.split(second), stdin=p1.stdout, stdout=subprocess.PIPE)

However it usually makes more sense to specify the commands directly:

first = ['ip', 'route', 'list', 'dev', 'eth0']
second = ['awk', ' /^default/ {print $3}']
p1 = subprocess.Popen(first, stdout=subprocess.PIPE)
p2 = subprocess.Popen(second, stdin=p1.stdout, stdout=subprocess.PIPE)

answered Mar 14, 2013 at 16:06

ecatmur

158k28 gold badges311 silver badges387 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Cyrille · Accepted Answer · 2013-03-14 16:08:03Z

4

Not the best solution, but while you are waiting for the best answer, you can still do this :

cmd = "ip route list dev eth0 | awk ' /^default/ {print $3}'"
p2 = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, shell=True)

answered Mar 14, 2013 at 16:08

Cyrille

14.7k3 gold badges30 silver badges42 bronze badges

3 Comments

Ricky Robinson Over a year ago

Interesting. I thought I had to split the command like I did above. Is there any difference if, like your example, I don't do it?

Cyrille Over a year ago

In this example, you don't have to split the command because shell=True but that's not safe (shell injection)

jfs Over a year ago

Drop stdin=subprocess.PIPE. Also output = subprocess.check_output(cmd, shell=True)

Collectives™ on Stack Overflow

awk from Python: wrong subprocess arguments?

2 Answers 2

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related