Hiding console output produced by os.system
Write directly to the proc pseudo file instead via Python i/o lib.
This will require your script to run as root (via sudo
), which means you should limit its scope to being an admin only tool. This also allows the script to run on boxes where sudo
requires a password.
Example:
with open("/proc/sys/vm/drop_caches", "w") as drop_caches:
drop_caches.write("3")
To answer the question based on its title in the most generic form:
To suppress all output from os.system()
, append >/dev/null 2>&1
to the shell command, which silences both stdout and stderr; e.g.:
import os
os.system('echo 3 | sudo tee /proc/sys/vm/drop_caches >/dev/null 2>&1')
Note that os.system()
by design passes output from the calling process' stdout and stderr streams through to the console (terminal) - your Python code never sees them.
Also, os.system()
does not raise an exception if the shell command fails and instead returns an exit code; note that it takes additional work to extract the shell command's true exit code: you need to extract the high byte from the 16-bit value returned, by applying >> 8
(although you can rely on a return value other than 0
implying an error condition).
Given the above limitations of os.system()
, it is generally worthwhile to use the functions in the subprocess
module instead:
For instance, subprocess.check_output()
could be used as follows:
import subprocess
subprocess.check_output('echo 3 | sudo tee /proc/sys/vm/drop_caches', shell=True)
The above will:
- capture stdout output and return it (with the return value being ignored in the example above)
- pass stderr output through; passing
stderr=subprocess.STDOUT
as an additional argument would also capture stderr. - raise an error, if the shell command fails.
Note: Python 3.5 introduced subprocess.run()
, a more flexible successor to both os.system()
and subprocess.check_output()
- see https://docs.python.org/3.5/library/subprocess.html#using-the-subprocess-module
Note:
- The reason that the OP is employing
tee
in the first place - despite not being interested in stdout output - is that a naïve attempt to use> ...
instead would be interpreted beforesudo
is invoked, and thus fail, because the required privileges to write to/proc/sys/...
haven't been granted yet. - Whether you're using
os.system()
or asubprocess
function, stdin is not affected by default, so if you're invoking your script from a terminal, you'll get an interactive password prompt when thesudo
command is encountered (unless the credentials have been cached).
subprocess.check_call(command,stdin=subprocess.DEVNULL, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
you forgot to add stderr.