Update APT cache:
manlix@lab:~$ sudo apt update
Install watch utility (package procps):
manlix@lab:~$ sudo apt install -y procps
Watching highlight output for date updated every 1 second
manlix@lab:~$ watch -n1 -d date
-n1 — update interval (1 second)
-d — highlight the differences between successive updates
Watching hightlight output changes for date since 1st run:
manlix@lab:~$ watch -n1 -d=1 date
-n1 — update interval (1 second)
-d=1 — incremental highlight the differences between successive updates