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How can I run an infinite loop in the background, while continuing on with the script's execution?
Example "script":
while true; do something_in_the_background; done
do_something_while_the_loop_goes_on_in_the_background
for 1 2 3; do somethingelse; done
exit 0
This (notice the &) seems to crash the whole system after a short while:
while true; do
something_in_the_background &
done
do_something_while_the_loop_goes_on_in_the_background
for 1 2 3; do somethingelse; done
exit 0
With the & inside the loop it will start a new process in the background and as fast as it can do it again without waiting for the first process to end. Instead I think you want to put the loop into the background, so put the & on the loop itself like
while /bin/true; do
something_in_the_background
done &
# more stuff
& will put the loop into the background. If you're doing this from an interactive shell, or one with job control enabled, you can do fg to bring background jobs to the fore. This loop will not have its own PID though, it will be just one of the things that the parent is doing. Killing the script should also terminate the loop if you're doing it that way. Alternately, you could change the while condition to test for, say, the existence of file and have it exit when the file no longer exists
Jul 7, 2020 at 22:10
echo "test" | tee -a $REPORT_FILE , then the whole terminal will have this output. How do you prevent this ?
tee will write to the terminal, so if you're ruining a command like that it will indeed run a lot of them at once and fill the screen
Oct 12, 2020 at 13:18
nohup and still use tee. So, it won't print in the terminal. Thanks for pointing that out and your solution works great. TQ.
while : ; do something ; done &
Earlier Bourne shells didn't have true and false as built-in commands. true was instead simply aliased to :, and false to something like let 0.
& at the end of the line backgrounds the process
: is the null command, as described by "help :": No effect; the command does nothing. Exit Status: Always succeeds.
: means and probably doesn't know why you've moved the & to the end. Also, changing the spacing to make it a one-liner is just confusing—it's a change which is very visible but is entirely unimportant.
Putting sleep of say .1 or .01 seconds would make your loop more CPU friendly. But as pointed out be Eric Renouf, the & should be at the end of the loop, not inside it.
