watch - execute a program periodically, showing output
fullscreen
SYNOPSIS
watch [-dhv] [-n <seconds>] [--differences[=cumulative]]
[--help] [--interval=<seconds>] [--version] <command>
DESCRIPTION
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 differ
ent interval.
The -d or --differences flag will highlight the differ
ences 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
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
watch uname -r
(Just kidding.)
BUGS
Upon terminal resize, the screen will not be correctly
repainted until the next scheduled update. All --differ
ences 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.
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