The watch command

watch - execute a program periodically, showing output fullscreen

SYNOPSIS
watch [-dhv] [-n ] [--differences[=cumulative]] [--help]
[--interval=] [--version]

DESCRIPTION
watch runs command repeatedly, displaying its output (the first screen-
full). 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.

watch will run until interrupted.

EXAMPLES
To watch for mail, you might do

watch -n 60 from

To watch the contents of a directory change, you could use

watch -d ls -l