watch [-dhv] [-n
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
watch will run until interrupted.
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