watch.1 4.34 KB
Newer Older
1
.TH WATCH 1 "2016-06-03" "procps-ng" "User Commands"
csmall's avatar
csmall committed
2 3 4 5
.SH NAME
watch \- execute a program periodically, showing output fullscreen
.SH SYNOPSIS
.B watch
6
[\fIoptions\fR] \fIcommand\fR
csmall's avatar
csmall committed
7
.SH DESCRIPTION
Jan Görig's avatar
Jan Görig committed
8
.B watch
csmall's avatar
csmall committed
9 10
runs
.I command
11
repeatedly, displaying its output and errors (the first screenfull).  This
12 13
allows you to watch the program output change over time.  By default,
\fIcommand\fR is run every 2 seconds and \fBwatch\fR will run until interrupted.
14 15
.SH OPTIONS
.TP
16 17 18 19
\fB\-d\fR, \fB\-\-differences\fR [\fIpermanent\fR]
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.
20 21 22
.TP
\fB\-n\fR, \fB\-\-interval\fR \fIseconds\fR
Specify update interval.  The command will not allow quicker than 0.1 second
23 24
interval, in which the smaller values are converted. Both '.' and ',' work
for any locales.
25 26 27
.TP
\fB\-p\fR, \fB\-\-precise\fR
Make
28 29 30 31 32 33 34
.BR watch
attempt to run
.I command
every
.I interval
seconds. Try it with
.B ntptime
35 36 37 38 39 40 41 42 43 44 45
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
46
Freeze updates on command error, and exit after a key press.
47
.TP
48 49 50 51 52
\fB\-g\fR, \fB\-\-chgexit\fR
Exit when the output of
.I command
changes.
.TP
53
\fB\-c\fR, \fB\-\-color\fR
54
Interpret ANSI color and style sequences.
55 56
.TP
\fB\-x\fR, \fB\-\-exec\fR
csmall's avatar
csmall committed
57
.I command
58 59
is given to
.B sh \-c
csmall's avatar
csmall committed
60
which means that you may need to use extra quoting to get the desired effect.
61 62 63 64 65 66 67 68 69
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.
70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104
.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
Closing 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 NOTES
POSIX option processing is used (i.e., option processing stops at
Jan Görig's avatar
Jan Görig committed
105
the first non\-option argument).  This means that flags after
csmall's avatar
csmall committed
106 107 108 109
.I command
don't get interpreted by
.BR watch
itself.
110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144
.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.

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
.I \-\-differences
mode.  Only the base character counts.

Blank lines directly after a line which ends in the last column do not
display.

.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).
csmall's avatar
csmall committed
145 146 147 148 149 150 151 152 153 154
.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
155
If you're only interested in files owned by user joe, you might use
csmall's avatar
csmall committed
156 157 158 159 160 161
.IP
watch \-d 'ls \-l | fgrep joe'
.PP
To see the effects of quoting, try these out
.IP
watch echo $$
Jan Görig's avatar
Jan Görig committed
162
.br
csmall's avatar
csmall committed
163
watch echo '$$'
Jan Görig's avatar
Jan Görig committed
164
.br
csmall's avatar
csmall committed
165 166
watch echo "'"'$$'"'"
.PP
167 168 169 170 171 172
To see the effect of precision time keeping, try adding
.I \-p
to
.IP
watch \-n 10 sleep 1
.PP
csmall's avatar
csmall committed
173 174
You can watch for your administrator to install the latest kernel with
.IP
Jan Görig's avatar
Jan Görig committed
175
watch uname \-r
csmall's avatar
csmall committed
176
.PP
177 178 179 180 181
(Note that
.I \-p
isn't guaranteed to work across reboots, especially in the face of
.B ntpdate
or other bootup time-changing mechanisms)