watch(1) - phpMan
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, the program is
run every 2 seconds. By default, watch 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 inter‐
val, in which the smaller values are converted.
Make watch attempt to run command every interval seconds. Try it with ntptime and
notice how the fractional seconds stays (nearly) the same, as opposed to normal
mode where they continuously increase.
Turn off the header showing the interval, command, and current time at the top of
the display, as well as the following blank line.
Beep if command has a non-zero exit.
Freeze updates on command error, and exit after a key press.
Exit when the output of command changes.
Interpret ANSI color sequences.
command is given to sh -c 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
Display help text and exit.
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 command don't get interpreted by watch
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
or other bootup time-changing mechanisms)
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 char‐
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
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 Closign 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 original watch was written by Tony Rems ⟨rembo AT unisoft.com⟩ in 1991, with mods and
corrections by Francois Pinard. It was reworked and new features added by Mike Coleman
⟨mkc AT acm.org⟩ in 1999. The beep, exec, and error handling features were added by Morty
Abzug ⟨morty AT frakir.org⟩ in 2008. On a not so dark and stormy morning in March of 2003,
Anthony DeRobertis ⟨asd AT suespammers.org⟩ 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 Jarrod Lowe ⟨procps AT rrod.net⟩
procps-ng June 2011 WATCH(1)