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WATCH(1) User Commands WATCH(1)
NAME
watch - execute a program periodically, showing output fullscreen
SYNOPSIS
watch [options] command
DESCRIPTION
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.
OPTIONS
-d, --differences[=permanent]
Highlight the differences between successive updates. If the optional permanent ar-
gument 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 inter-
val, in which the smaller values are converted. Both '.' and ',' work for any lo-
cales. 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 op-
posed 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.
-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 quot-
ing to get the desired effect.
-w, --no-linewrap
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.
EXIT STATUS
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.
ENVIRONMENT
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.
NOTES
POSIX option processing is used (i.e., option processing stops at the first non-option ar-
gument). This means that flags after command don't get interpreted by watch itself.
BUGS
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 com-
mand 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 char-
acter 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 pre-
vious executions running longer than --interval (for example, netstat taking ages on a DNS
lookup).
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 "'"'$$'"'"
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)
procps-ng 2020-12-06 WATCH(1)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2025-04-23 15:47 @3.147.48.161 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)