81f64657ba
Add new flags to watch (-g/--chgexit) so that it exits when the output changes. This is useful in builds and shell scripts, for example when deploying webapps to block the remainder of the deployment steps until after the webapp starts. e.g. watch --chgexit curl http://foo/bar
208 lines
4.8 KiB
Groff
208 lines
4.8 KiB
Groff
.TH WATCH "1" "June 2011" "procps-ng" "User Commands"
|
|
.SH NAME
|
|
watch \- execute a program periodically, showing output fullscreen
|
|
.SH SYNOPSIS
|
|
.B watch
|
|
[\fIoptions\fR] \fIcommand\fR
|
|
.SH DESCRIPTION
|
|
.B watch
|
|
runs
|
|
.I 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,
|
|
.B watch
|
|
will run until interrupted.
|
|
.SH OPTIONS
|
|
.TP
|
|
\fB\-d\fR, \fB\-\-differences\fR
|
|
Highlight the differences between successive updates.
|
|
.TP
|
|
\fB\-n\fR, \fB\-\-interval\fR \fIseconds\fR
|
|
Specify update interval. The command will not allow quicker than 0.1 second
|
|
interval, in which the smaller values are converted.
|
|
.TP
|
|
\fB\-p\fR, \fB\-\-precise\fR
|
|
Make
|
|
.BR watch
|
|
attempt to run
|
|
.I command
|
|
every
|
|
.I interval
|
|
seconds. Try it with
|
|
.B ntptime
|
|
and notice how the fractional seconds stays (nearly) the same, as opposed to
|
|
normal mode where they continuously increase.
|
|
.TP
|
|
\fB\-t\fR, \fB\-\-no\-title\fR
|
|
Turn off the header showing the interval, command, and current time at the
|
|
top of the display, as well as the following blank line.
|
|
.TP
|
|
\fB\-b\fR, \fB\-\-beep\fR
|
|
Beep if command has a non-zero exit.
|
|
.TP
|
|
\fB\-e\fR, \fB\-\-errexit\fR
|
|
Freeze updates on command error, and exit after a key press.
|
|
.TP
|
|
\fB\-g\fR, \fB\-\-chgexit\fR
|
|
Exit when the output of
|
|
.I command
|
|
changes.
|
|
.TP
|
|
\fB\-c\fR, \fB\-\-color\fR
|
|
Interpret ANSI color sequences.
|
|
.TP
|
|
\fB\-x\fR, \fB\-\-exec\fR
|
|
.I command
|
|
is given to
|
|
.B 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
|
|
.BR exec (2)
|
|
instead.
|
|
.TP
|
|
\fB\-h\fR, \fB\-\-help\fR
|
|
Display help text and exit.
|
|
.TP
|
|
\fB\-v\fR, \fB\-\-version\fR
|
|
Display version information and exit.
|
|
.SH NOTE
|
|
Note that POSIX option processing is used (i.e., option processing stops at
|
|
the first non\-option argument). This means that flags after
|
|
.I command
|
|
don't get interpreted by
|
|
.BR watch
|
|
itself.
|
|
.SH EXAMPLES
|
|
.PP
|
|
To watch for mail, you might do
|
|
.IP
|
|
watch \-n 60 from
|
|
.PP
|
|
To watch the contents of a directory change, you could use
|
|
.IP
|
|
watch \-d ls \-l
|
|
.PP
|
|
If you're only interested in files owned by user joe, you might use
|
|
.IP
|
|
watch \-d 'ls \-l | fgrep joe'
|
|
.PP
|
|
To see the effects of quoting, try these out
|
|
.IP
|
|
watch echo $$
|
|
.br
|
|
watch echo '$$'
|
|
.br
|
|
watch echo "'"'$$'"'"
|
|
.PP
|
|
To see the effect of precision time keeping, try adding
|
|
.I \-p
|
|
to
|
|
.IP
|
|
watch \-n 10 sleep 1
|
|
.PP
|
|
You can watch for your administrator to install the latest kernel with
|
|
.IP
|
|
watch uname \-r
|
|
.PP
|
|
(Note that
|
|
.I \-p
|
|
isn't guaranteed to work across reboots, especially in the face of
|
|
.B ntpdate
|
|
or other bootup time-changing mechanisms)
|
|
.SH BUGS
|
|
Upon terminal resize, the screen will not be correctly repainted until the
|
|
next scheduled update. All
|
|
.B \-\-differences
|
|
highlighting is lost on that update as well.
|
|
.PP
|
|
Non-printing characters are stripped from program output. Use "cat -v" as
|
|
part of the command pipeline if you want to see them.
|
|
.PP
|
|
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.
|
|
.PP
|
|
Combining Characters never count as different in
|
|
.I \-\-differences
|
|
mode. Only the base character counts.
|
|
.PP
|
|
Blank lines directly after a line which ends in the last column do not
|
|
display.
|
|
.PP
|
|
.I \-\-precise
|
|
mode doesn't yet have advanced temporal distortion technology to compensate
|
|
for a
|
|
.I command
|
|
that takes more than
|
|
.I interval
|
|
seconds to execute.
|
|
.B watch
|
|
also can get into a state where it rapid-fires as many executions of
|
|
.I command
|
|
as it can to catch up from a previous executions running longer than
|
|
.I interval
|
|
(for example,
|
|
.B netstat
|
|
taking ages on a DNS lookup).
|
|
.SH "EXIT STATUS"
|
|
.PP
|
|
.RS
|
|
.PD 0
|
|
.TP
|
|
.B 0
|
|
Success.
|
|
.TP
|
|
.B 1
|
|
Various failures.
|
|
.TP
|
|
.B 2
|
|
Forking the process to watch failed.
|
|
.TP
|
|
.B 3
|
|
Replacing child process stdout with write side pipe failed.
|
|
.TP
|
|
.B 4
|
|
Command execution failed.
|
|
.TP
|
|
.B 5
|
|
Closign child process write pipe failed.
|
|
.TP
|
|
.B 7
|
|
IPC pipe creation failed.
|
|
.TP
|
|
.B 8
|
|
Getting child process return value with
|
|
.BR waitpid (2)
|
|
failed, or command exited up on error.
|
|
.TP
|
|
.B other
|
|
The watch will propagate command exit status as child exit status.
|
|
.SH AUTHORS
|
|
The original
|
|
.B watch
|
|
was written by
|
|
.UR rembo\@\:unisoft.\:com
|
|
Tony Rems
|
|
.UE
|
|
in 1991, with mods and
|
|
corrections by Francois Pinard. It was reworked and new features added by
|
|
.UR mkc\@\:acm.\:org
|
|
Mike Coleman
|
|
.UE
|
|
in 1999. The beep, exec, and error handling features were added by
|
|
.UR morty\@\:frakir.\:org
|
|
Morty Abzug
|
|
.UE
|
|
in 2008. On a not so dark and stormy morning in March of 2003,
|
|
.UR asd\@\:suespammers.\:org
|
|
Anthony DeRobertis
|
|
.UE
|
|
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
|
|
.UR procps\@\:rrod.\:net
|
|
Jarrod Lowe
|
|
.UE
|