Why can I run this command from the terminal but I get an error when my python runs it from the terminal for me?

Question

I'm trying to write a python script that basically captures webcam videos from the terminal. When I put the command in a string and use subprocess.call(script, True), I get an error, but when I literally copy/paste the same command to the terminal it works fine.

This is my python:

import subprocess
import os
if (os.path.isdir("Videos/Webcam/temp") is False):
    dirmake = 'mkdir Videos/Webcam/temp'
    subprocess.call(dirmake, True)
cmd = 'ffmpeg -f v4l2 -i /dev/video0 -t 00:00:10 video.webm'
subprocess.call(cmd, True)

and this is the error

`FileNotFoundError: [Errno 2] No such file or directory: 'ffmpeg -f v4l2 -i /dev/video0 -t 00:00:10 video.webm': 'ffmpeg -f v4l2 -i /dev/video0 -t 00:00:10 video.webm'`

If I just run ffmpeg -f v4l2 -i /dev/video0 -t 00:00:10 video.webm from the terminal it works fine.

Originally the video was supposed to go in Videos/Webcam/temp but I took it out to see if the error had something to do with where I was putting the video. I'm using Ubuntu 18.04.2 LTS if that makes a difference.

I think that sub process takes a list of strings, not a single string. — quamrana
– quamrana, Commented May 9, 2019 at 20:48

witty-user-name · Accepted Answer · 2019-05-09 21:07:24Z

2

When using the subprocess module you will typically pass it your command as a list of strings, rather than the entire command you wish to run.

For example, rather than subprocess.call('ls -l /my/dir'), which will give an error, you would use subprocess.call(['ls', '-l', '/my/dir'])

See more on the subprocess module here

answered May 9, 2019 at 21:07

witty-user-name

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