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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | KEY CONTROL | EXIT STATUS | ENVIRONMENT | NOTES | EXAMPLES | BUGS | REPORTING BUGS | COLOPHON |
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WATCH(1) User Commands WATCH(1)
watch - execute a program periodically, showing output fullscreen
watch [option ...] command
watch runs command repeatedly, displaying its output and errors
(the first screenful). 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. A header informs
of the start and running time of command as well as its exit
code.
-b, --beep
Beep if command has a non-zero exit.
-c, --color
Interpret ANSI color and style sequences.
-C, --no-color
Do not interpret ANSI color and style sequences.
-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.
-e, --errexit
Freeze updates on command error, and exit after a key
press. The exit code of watch will be the code command
exits with. If signal n is the cause of command
termination, the exit code will be 128 + n.
-g, --chgexit
Exit when the output of command changes.
-n, --interval seconds
Specify update interval. Values smaller than 0.1 and
larger than 2678400 (31 days) are converted into these
respective bounds. Both '.' and ',' work for any locale.
The WATCH_INTERVAL environment variable can be used to
persistently set a non-default interval (following the
same rules and formatting).
-p, --precise
Execute command --interval seconds after its previous run
started, instead of --interval seconds after its previous
run finished. If it's taking longer than --interval
seconds for command to complete, it is waited for in
either case.
-q, --equexit <cycles>
Exit when output of command does not change for the given
number of cycles.
-r, --no-rerun
Do not run the program on terminal resize, the output of
the program will re-appear at the next regular run time.
-s, --shotsdir
Directory to save screenshots into.
-t, --no-title
Turn off the header normally shown at the top of the
screen.
-w, --no-wrap
Turn off line wrapping. Long lines will be truncated
instead of wrapped to the next line.
-x, --exec
Pass command to an exec(3) call instead of sh -c. The
program will start a bit quicker. Shell features
(environment setup, variable and pathname expansion, etc.)
will be unavailable.
-h, --help
Display help text and exit.
-v, --version
Display version information and exit.
spacebar
Issue command immediately. If it's running at the moment,
it is not interrupted and its next round will start
without delay.
q Quit watch. It currently does not interrupt a running
command (as opposed to terminating signals, such as the
SIGKILL following Ctrl+C).
s Take a screenshot. It will be saved in the working
directory, unless specified otherwise by --shotsdir. If
command is running at the moment, the screenshot will be
taken as soon as it finishes.
0 Success. Does not represent command exit code.
1 Errors unrelated to command operation.
2 Errors related to command execution and management (not
its exit code).
any non-zero (--errexit)
With --errexit the last exit code of command is returned.
The behavior of watch is affected by the following environment
variables.
WATCH_INTERVAL
Update interval, follows the same rules as the --interval
command line option.
COLUMNS
Terminal screen character width. Set to override
autodetection.
LINES Terminal screen character height. Set to override
autodetection.
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.
Non-printing characters are stripped from program output. Use cat
-v as part of the command pipeline if you want to see them.
To watch the contents of a directory change, you could use
watch -d ls -l
If you have CPUs with a dynamic frequency and want to observe it
change, try the following. The command is passed to the shell,
which allows you to make the pipeline. The quotes are a feature
of the shell too.
watch -n1 'grep "^cpu MHz" /proc/cpuinfo | sort -nrk4'
To monitor the up status of your servers, saving a copy of the
output of each run to a file, you may use this. The -p makes the
command execute every 10 seconds regardless of how long it took
to complete the previous run.
watch -n10 -p -d '{ date; for i in 10.0.0.31 10.0.0.32
10.0.0.33; do R=OK; ping -c2 -W2 "$i" &>/dev/null ||
R=FAIL; echo "$i: $R"; done } | tee -a ~/log'
You can watch for your administrator to install the latest kernel
with
watch uname -r
When the terminal dimensions change, its contents changes are not
registered on the next command run. --chgexit will not trigger
that turn and the counter of --equexit will not restart even if
command output changes meanwhile. --differences highlighting is
reset.
Please send bug reports to ⟨[email protected]⟩.
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 2024-06-14. (At
that time, the date of the most recent commit that was found in
the repository was 2024-06-04.) 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
[email protected]
procps-ng 2023-07-31 WATCH(1)
Pages that refer to this page: lsblk(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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