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.
Highlight the differences between successive updates. If the
optional =permanent argument is specified then watch will show
all changes since the first iteration.
-n, --interval seconds
Specify update interval. The command will not allow quicker
than 0.1 second interval, in which the smaller values are
converted. Both '.' and ',' work for any locales. The
WATCH_INTERVAL environment can be used to persistently set a
non-default interval (following the same rules and
Make watch attempt to run command every interval seconds. Try
it with ntptime and notice how the fractional seconds stays
(nearly) the same, as opposed to normal mode where they
Turn off the header showing the interval, command, and current
time at the top of the display, as well as the following blank
Beep if command has a non-zero exit.
Freeze updates on command error, and exit after a key press.
Exit when the output of command changes.
Interpret ANSI color and style sequences.
Pass command to exec(2) instead of sh -c which reduces the
need to use extra quoting to get the desired effect.
Display help text and exit.
Display version information and exit.
1 Various failures.
2 Forking the process to watch failed.
3 Replacing child process stdout with write side pipe
4 Command execution failed.
5 Closing child process write pipe failed.
7 IPC pipe creation failed.
8 Getting child process return value with waitpid(2)
failed, or command exited up on error.
other The watch will propagate command exit status as child
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
--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
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 "'"'$$'"'"
To see the effect of precision time keeping, try adding -p to
watch -n 10 sleep 1
You can watch for your administrator to install the latest kernel
watch uname -r
(Note that -p isn't guaranteed to work across reboots, especially in
the face of ntpdate or other bootup time-changing mechanisms)
This page is part of the procps-ng (/proc filesystem utilities)
project. Information about the project can be found at
⟨https://gitlab.com/procps-ng/procps⟩. If you have a bug report for
this manual page, see
This page was obtained from the project's upstream Git repository
⟨https://gitlab.com/procps-ng/procps.git⟩ on 2020-06-09. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-06-04.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to firstname.lastname@example.org
procps-ng 2020-06-04 WATCH(1)