Redirecting stdio from a command in os.system() in Python

Question

Usually I can change stdout in Python by changing the value of sys.stdout. However, this only seems to affect print statements. So, is there any way I can suppress the output (to the console), of a program that is run via the os.system() command in Python?

Solution 1

You could consider running the program via subprocess.Popen, with subprocess.PIPE communication, and then shove that output where ever you would like, but as is, os.system just runs the command, and nothing else.

from subprocess import Popen, PIPE

p = Popen(['command', 'and', 'args'], stdout=PIPE, stderr=PIPE, stdin=PIPE)

output = p.stdout.read()
p.stdin.write(input)

Much more flexible in my opinion. You might want to look at the full documentation: Python Subprocess module

Solution 2

On a unix system, you can redirect stderr and stdout to /dev/null as part of the command itself.

os.system(cmd + "> /dev/null 2>&1")

Comments

[Xavier Combelle]

That don't do the job quote from docs.python.org/library/os.html#process-management os.system(command) Execute the command (a string) in a subshell. This is implemented by calling the Standard C function system(), and has the same limitations. Changes to sys.stdin, etc. are not reflected in the environment of the executed command.

[Leif Andersen]

Mmm...okay. So than the command is executed on the line P = Popen(...), yes? And it will only show the output when calling p.stdout.read()...yes? Thank you

[Leif Andersen]

Okay...the commands did run, but in a separate thread. Is there anyway I can either hault the program while the commands run, or keep it in the same thread? Thank you.

[Blue Peppers]

Simply, use p.wait(). However, apparently this can result in deadlocking when using PIPE stdout if the program generates enough output. See the full documentation at docs.python.org/library/subprocess.html#subprocess.Popen.wai‌​t . However, I think it should work..

[Leif Andersen]

Hmm...okay, thanks. Also, it appears that using p.communicate() (rather than p.stdout will help clear the pipe. Thanks.

[spurra]

This was the answer I was looking for and should've been the accepted answer.