I have a Python 3 program that uses the os process to run the "cat" command.

This is the code fragment, it wirks great, but all the output ends up on the screeen.

os.system("cat *.txt | tee output.txt")

How can I suppress the output from appearing on the screen?

Thanks for any help or suggestions.

CodePudding user response：

Avoiding The Problem Altogether

tee writes to stdout. If you don't want to write to stdout, don't use tee:

os.system("cat -- *.txt >output.txt")

Redirecting Stdout Away

If you do want to use tee, you can explicitly redirect away its stdout:

os.system('cat -- *.txt | tee output.txt >/dev/null')

Using subprocess.run With stdout=subprocess.DEVNULL

If you don't want to modify the shell command to add a redirection within it, subprocess.run gives you enough power to specify redirections to perform before starting a shell:

import subprocess

subprocess.run('cat -- *.txt | tee output.txt', shell=True,
               stdout=subprocess.DEVNULL)

Using subprocess.run Without tee Or A Shell

...but it's more efficient and less prone to security issues if you just don't use a shell at all:

import subprocess, glob

subprocess.run(['cat', '--']   glob.glob('*.txt'),
               stdout=open('output.txt', 'w'))

Using subprocess.run With Tee, But Without A Shell

If you're up for not using a shell at all, but your real-world use case unconditionally includes some analogue to tee, the Python standard-library documentation describes how to accomplish this at https://docs.python.org/3/library/subprocess.html#replacing-shell-pipeline, as demonstrated below:

import subprocess, glob
p1 = subprocess.Popen(['cat', '--']   glob.glob('*.txt'), stdout=subprocess.PIPE)
p2 = subprocess.Popen(['tee', 'output.txt', stdin=p1.stdout, stdout=subprocess.DEVNULL)
p1.stdout.close()
p2.communicate()

CodePudding user response：

You shall take care about the default shell used by os.system

Try to execute this to check the shell used in background:

python3 -c 'import os; os.system("ps $$")'

You can change your code a little bit to force the bash shell and redirect the output to /dev/null:

os.system('/bin/bash -c "cat *.txt | tee output.txt &>/dev/null"')

Note that regardless of the technique (you could use subprocess module) the point is the background shell and the output redirection.