Section: User Commands (1)
Updated: June 2011Index
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watch - execute a program periodically, showing output fullscreen
repeatedly, displaying its output and errors (the first screenfull). This
allows you to watch the program output change over time. By default, the
program is run every 2 seconds.
will run until interrupted.
- -d, --differences [permanent]
Highlight the differences between successive updates. Option will read
optional argument that changes highlight to be permanent, allowing to see what
has changed at least once since 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.
- -p, --precise
attempt to run
seconds. Try it with
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
- -c, --color
Interpret ANSI color sequences.
- -x, --exec
is given to
which means that you may need to use extra quoting to get the desired effect.
This with the --exec option, which passes the command to
- -h, --help
Display help text and exit.
- -v, --version
Display version information and exit.
Note that POSIX option processing is used (i.e., option processing stops at
the first non-option argument). This means that flags after
don't get interpreted by
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
watch -n 10 sleep 1
You can watch for your administrator to install the latest kernel with
watch uname -r
isn't guaranteed to work across reboots, especially in the face of
or other bootup time-changing mechanisms)
Upon terminal resize, the screen will not be correctly repainted until the
next scheduled update. All
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
mode. Only the base character counts.
Blank lines directly after a line which ends in the last column do not
mode doesn't yet have advanced temporal distortion technology to compensate
that takes more than
seconds to execute.
also can get into a state where it rapid-fires as many executions of
as it can to catch up from a previous executions running longer than
taking ages on a DNS lookup).
Forking the process to watch failed.
Replacing child process stdout with write side pipe failed.
Command execution failed.
Closign child process write pipe failed.
IPC pipe creation failed.
Getting child process return value with
failed, or command exited up on error.
The watch will propagate command exit status as child exit status.
was written by
in 1991, with mods and
corrections by Francois Pinard. It was reworked and new features added by
in 1999. The beep, exec, and error handling features were added by
in 2008. On a not so dark and stormy morning in March of 2003,
got sick of his watches that should update every minute eventually updating
many seconds after the minute started, and added microsecond precision.
Unicode support was added in 2009 by
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