watch - execute a program periodically, showing output fullscreen
DESCRIPTION watch runs command repeatedly, displaying its output (the first screenfull). This allows you to watch the program output change over time. By default, the program is run every 2 seconds; use -n or –interval to specify a different interval.
The -d or --differences flag will highlight the differences between successive updates. The --cumulative option makes highlighting "sticky", presenting a running display of all positions that have ever changed. The -t or --no-title option turns off the header showing the interval, command, and current time at the top of the display, as well as the following blank line. watch will run until interrupted.
watch comes with the package “procps” under CentOS
It can be useful in debugging/testing stuff/…