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
- 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 "’"’$$’"’"
To see the effect of precision time keeping, try adding -p to
- watch -n 10 sleep 1
You can watch for your administrator to install the latest kernel with
- watch uname -r
(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.