watch – Periodically run and show the output of a program
Watch runs command repeatedly, displaying its output This allows you to monitor the program output change over time.
$ watch ls — Every 2sec(default time) ‘ls’ is executed and output is showed on the screen.
$ watch -n 6 who — Every 6Sec ‘who’ run and list the current users
$ watch -d date — Highlight the difference b/w successive updates
Press Ctrl+C to stop the Watch Command.
Read: man watch