How to suppress or capture the output of subprocess.run()?

Here is how to suppress output, in order of decreasing levels of cleanliness. They assume you are on Python 3.

1. You can redirect to the special subprocess.DEVNULL target.

import subprocesssubprocess.run(['ls', '-l'], stdout=subprocess.DEVNULL)# The above only redirects stdout...# this will also redirect stderr to /dev/null as wellsubprocess.run(['ls', '-l'], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)# Alternatively, you can merge stderr and stdout streams and redirect# the one stream to /dev/nullsubprocess.run(['ls', '-l'], stdout=subprocess.DEVNULL, stderr=subprocess.STDOUT)

2. If you want a fully manual method, can redirect to /dev/null by opening the file handle yourself. Everything else would be identical to method #1.

import osimport subprocesswith open(os.devnull, 'w') as devnull:    subprocess.run(['ls', '-l'], stdout=devnull)

Here is how to capture output (to use later or parse), in order of decreasing levels of cleanliness. They assume you are on Python 3.

1. If you simply want to capture both STDOUT and STDERR independently, AND you are on Python >= 3.7, use capture_output=True.

import subprocessresult = subprocess.run(['ls', '-l'], capture_output=True)print(result.stdout)print(result.stderr)

2. You can use subprocess.PIPE to capture STDOUT and STDERR independently. This does work on Python versions < 3.7, such as Python 3.6.

import subprocessresult = subprocess.run(['ls', '-l'], stdout=subprocess.PIPE)print(result.stdout)# To also capture stderr...result = subprocess.run(['ls', '-l'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)print(result.stdout)print(result.stderr)# To mix stdout and stderr into a single stringresult = subprocess.run(['ls', '-l'], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)print(result.stdout)

NOTE: By default, captured output is returned as bytes. If you want to capture as text (e.g. str), use universal_newlines=True (or on Python >=3.7, use the infinitely more clear and easy-to-understand option text=True - it's the same as universal_newlines but with a different name).

ex: to capture the output of ls -a

import subprocessls = subprocess.run(['ls', '-a'], capture_output=True, text=True).stdout.strip("\n")print(ls)