Python subprocess.check_output, with pipeline

Question

I'm trying to get output of

dmesg | grep -i 'bios'

I've tried this:

dmsg = subprocess.check_output("dmesg | grep -i 'bios'").decode('utf-8')

, but I'm getting an error.

How can I obtain a full sdtoutput message?

What error are you receiving? You typically must give the command and parameters as elements in a list, not as a single string. See the documentation — Bob Dylan
– Bob Dylan, Commented Aug 24, 2015 at 20:45

Joseph Stover · Accepted Answer · 2015-08-24 21:34:26Z

import subprocess p1 = subprocess.Popen(['dmesg'], stdout=subprocess.PIPE) p2 = subprocess.Popen(['grep', '-i', 'bios'], stdin=p1.stdout, stdout=subprocess.PIPE) p1.stdout.close() out, err = p2.communicate() print(out)

Padraic Cunningham · Accepted Answer · 2015-08-24 21:42:05Z

You can pipe using Popen passing the stdout of one one process to the stdin of another but you also parse the output of dmesg with python instead of running two processes:

import subprocess dmsg = subprocess.check_output("dmesg",universal_newlines=True).splitlines() print([line for line in dmsg if "bios" in line.lower()])

If you were trying to pipe using check_output you would need to use shell=True:

import subprocess dmsg = subprocess.check_output("dmesg | grep -i 'bios'",shell=True).decode('utf-8')

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