Any way to assign terminal output to variable with python?

Question

I need to grab the duration of a video file via python as part of a larger script. I know I can use ffmpeg to grab the duration, but I need to be able to save that output as a variable back in python. I thought this would work, but it's giving me a value of 0:

cmd = 'ffmpeg -i %s 2>&1 | grep "Duration" | cut -d \' \' -f 4 | sed s/,//' % ("Video.mov")
duration = os.system(cmd)
print duration

Am I doing the output redirect wrong? Or is there simply no way to pipe the terminal output back into python?

Answer 1

os.system returns a return value indicating the success or failure of the command. It does not return the output from stdout or stderr. To grab the output from stdout (or stderr), use subprocess.Popen.

import subprocess
proc=subprocess.Popen('echo "to stdout"', shell=True, stdout=subprocess.PIPE, )
output=proc.communicate()[0]
print output

See the wonderfully written Python Module of the Week blog.

Answer 2

You probably want subprocess.Popen.

Answer 3

os.system returns the exit code of the executed command, not its output. To do this you would need to use either commands.getoutput (deprecated) or subprocess.Popen:

from subprocess import Popen, PIPE

stdout = Popen('your command here', shell=True, stdout=PIPE).stdout
output = stdout.read()