Watch has a nice difference flag, so that whatever is different from the last iteration is highlighted. As in:

watch -d sudo netstat -tnp

Closer to watch -

  while 1; do datetime; ls; sleep 2; done

I used to do:

  while true; do date; ls; sleep 2; clear; done

but got tired of it and searched apt for watch.

  apt-get install procps

I used to do:

  while true; do date; ls; sleep 2; clear; done

but got tired of that and installed procps via apt.

1: command not found

try this instead:

while true; do ls; sleep 5; done