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. The -t or --no-title option turns off the header showing the interval, --no-title option turns off the header showing the interval, command, and current time at the top of the display, as well as the following blank line.

watch will run until interrupted.

Note that POSIX option processing is used (i.e., option processing stops at the first non-option argument). This means that flags after command don't get interpreted by watch itself.

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

If you're only interested in files owned by user joe, you might use

watch -d 'ls -l | fgrep joe'

To see the effects of quoting, try these out

watch echo $$

watch echo '$$'

watch echo "'"'$$'"'"

You can watch for your administrator to install the latest kernel with

watch uname -r

(Just kidding.)

Non-printing characters are stripped from program output. Use "cat -v" as part of the command pipeline if you want to see them.