Hide output in Bash Script

Question

I have a bash script, but it gives me annoying output which I don't want to see. Of course I can hide it in that way:

./script.sh >/dev/null 2>&1

but I want to put the script in "rc.local" or "cron job", so it will be really bad if it received the output every 5 minutes for example, or on boot. It will be great if there is a way to tell the whole script to hide the output.

I'm not 100% sure what you're asking - if you never want to see the output, just redirect to /dev/null like you're doing. Perhaps provide a more concrete example of what you're trying to do? You might be interested in this question which discusses suppressing output only if the command succeeds. — dimo414
– dimo414, Commented Dec 16, 2015 at 0:39
Can't you just put ./script.sh >/dev/null 2>&1 in rc.local or crontab? — that other guy
– that other guy, Commented Dec 16, 2015 at 0:39

Charles Duffy · Accepted Answer · 2015-12-16 00:54:45Z

6

If you want to redirect all output to /dev/null within the script, that can be done like so (in this case, only performing the redirection if the environment variable DEBUG is not set):

#!/bin/bash
[[ $DEBUG ]] || exec >/dev/null 2>&1
# ...continue with execution here.

You could also check for whether your input is from a TTY to detect interactive use:

if [ -t 0 ]; then
  # being run by a human, be extra verbose
  PS4=':$LINENO+'
  set -x
else
  # being run by a daemon, be outright silent
  exec >/dev/null 2>&1
fi

See the bash-hackers page on the exec builtin.

edited Dec 16, 2015 at 0:54

answered Dec 16, 2015 at 0:42

Charles Duffy

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