UNIX/Linux Shell Watch Command
watch - execute a program periodically, showing output fullscreen
watch [
-dhvt] [
-n seconds] [
--differences[=cumulative]] [
--help] [
--interval=seconds]
[
--no-title] [
--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. 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 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.
