ou can use the watch command to execute a program or shell script periodically, display its output on screen repeatedly. This allows you to watch the program output change over time. By default, the program is run every 2 seconds. This is useful to monitor memory utilization or disk space usage over time without having to look at scrolling output.
Say hello to watch command
The watch command execute a program periodically, showing output in fullscreen mode. It runs command repeatedly, displaying its output. You can install gnuwatch under OpenBSD or cmdwatch under FreeBSD (see the comments for more information) to get the same result.