- Repeatedly run a command and show the result:watch [command]- Re-run a command every 60 seconds:watch -n  [command]- Monitor the contents of a directory, highlighting differences as they appear:watch -d [ls -l]
watch [options] command
watch runs command repeatedly, displaying its output and errors (the first screenfull). This allows you to watch the program output change over time. By default, command is run every 2 seconds and watch will run until interrupted.
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.
Upon terminal resize, the screen will not be correctly repainted until the next scheduled update. All --differences highlighting is lost on that update as well.
Non-printing characters are stripped from program output. Use "cat -v" as part of the command pipeline if you want to see them.
Combining Characters that are supposed to display on the character at the last column on the screen may display one column early, or they may not display at all.
Combining Characters never count as different in --differences mode. Only the base character counts.
Blank lines directly after a line which ends in the last column do not display.
--precise mode doesn't yet have advanced temporal distortion technology to compensate for a command that takes more than interval seconds to execute. watch also can get into a state where it rapid-fires as many executions of command as it can to catch up from a previous executions running longer than interval (for example, netstat taking ages on a DNS lookup).
To watch for 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)