Threads on Shell?

Question

Command line

The task is as follows: during the execution of the script, you need to pull one command every 30 seconds (" xscreensaver-command -deactivate >&- 2>&- &", if important). Ideally, I need fork (), but on a clean shell, I did not find how to implement it. I would like to do without bashisms and binding to a specific shell. There is only sh, dash, to be exact. Do not offer solutions with calling an external script and dynamically loading a special cron file, I myself will calmly write this, I need a solution to supplement the current script.

Answer 1

Move it to a separate script and run it with the same &? Or not even take it out, but run sh itself by passing it the necessary code.