WATCH

watch − execute a program periodically, showing output fullscreen

watch [−dhv] [−n <seconds>] [−−differences[=cumulative]] [−−help] [−−interval=<seconds>] [−−version] <command>

watch runs command repeatedly, displaying its output (the first screenfull). 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 changed.

watch will run until interrupted.

Note that command is given to "sh -c" which means that you may need to use extra quoting to get the desired effect.

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.)

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.

The original watch was written by Tony Rems <rembo@unisoft.com> in 1991, with mods and corrections by Francois Pinard. It was reworked and new features added by Mike Coleman <mkc@acm.org> in 1999.