|
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | ENVIRONMENT | NOTES | BUGS | EXAMPLES | COLOPHON |
|
|
|
WATCH(1) User Commands WATCH(1)
watch - execute a program periodically, showing output fullscreen
watch [options] command
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.
-d, --differences[=permanent]
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 formatting).
-p, --precise
Make watch attempt to run command every --interval
seconds. Try it with ntptime (if present) and notice how
the fractional seconds stays (nearly) the same, as opposed
to normal mode where they continuously increase.
-t, --no-title
Turn off the header showing the interval, command, and
current time at the top of the display, as well as the
following blank line.
-b, --beep
Beep if command has a non-zero exit.
-e, --errexit
Freeze updates on command error, and exit after a key
press.
-g, --chgexit
Exit when the output of command changes.
-q, --equexit <cycles>
Exit when output of command does not change for the given
number of cycles.
-c, --color
Interpret ANSI color and style sequences.
-x, --exec
Pass command to exec(2) instead of sh -c which reduces the
need to use extra quoting to get the desired effect.
-w, --no-wrap
Turn off line wrapping. Long lines will be truncated
instead of wrapped to the next line.
-h, --help
Display help text and exit.
-v, --version
Display version information and exit.
0 Success.
1 Various failures.
2 Forking the process to watch failed.
3 Replacing child process stdout with write side pipe
failed.
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 exit status.
The behaviour of watch is affected by the following environment
variables.
WATCH_INTERVAL
Update interval, follows the same rules as the --interval
command line option.
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.
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 not display.
--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
with
watch uname -r
(Note that -p isn't guaranteed to work across reboots, especially
in the face of ntpdate (if present) 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
⟨https://gitlab.com/procps-ng/procps/blob/master/Documentation/bugs.md⟩.
This page was obtained from the project's upstream Git repository
⟨https://gitlab.com/procps-ng/procps.git⟩ on 2022-12-18. (At
that time, the date of the most recent commit that was found in
the repository was 2022-12-13.) 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
man-pages@man7.org
procps-ng 2021-04-24 WATCH(1)
Pages that refer to this page: lsblk(8)
|
HTML rendering created 2022-12-18 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|