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 op-
tional 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 con-
verted. Both '.' and ',' work for any locales. The WATCH_INTER-
VAL 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 sec-
onds 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.
-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-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 vari-
ables.
WATCH_INTERVAL
Update interval, follows the same rules as the --interval com-
mand line option.
NOTES
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.
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 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).
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 mecha-
nisms)
procps-ng 2020-12-06 WATCH(1)
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