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. 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.
watch will run until interrupted.
NOTE
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.
EXAMPLES
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.)
BUGS
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.
AUTHORS
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.