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, command, and current time at the top of the display, as well as the following blank line. The -b or --beep option causes the command to beep if it has a non-zero exit.
watch will normally run until interrupted. If you want watch to exit on an error from the program running use the -e or --errexit options, which will cause watch to exit if the return value from the program is non-zero.
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 watchfor mail, you might do
To watch the contents of a directory change, you could use
If you’re only interested in files owned by user joe, you might use
To see the effects of quoting, try these out
To see the effect of precision time keeping, try adding -p to
You can watch for your administrator to install the latest kernel with
(Note that -p isn’t guaranteed to work across reboots, especially in the face of ntpdate or other bootup time-changing mechanisms)
Non-printing characters are stripped from program output. Use "cat -v" as part of the command pipeline if you want to see them.