How to run an infinite loop in the background

Question

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

Answer 1

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

Answer 2

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.

Answer 3

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.