1WATCH(1) User Commands WATCH(1)
2
6 watch - execute a program periodically, showing output fullscreen
7
9 watch [options] command
10
12 watch runs command repeatedly, displaying its output and errors (the
13 first screenfull). This allows you to watch the program output change
14 over time. By default, command is run every 2 seconds and watch will
15 run until interrupted.
16
18 -d, --differences[=permanent]
19 Highlight the differences between successive updates. If the op‐
20 tional permanent argument is specified then watch will show all
21 changes since the first iteration.
22 -n, --interval seconds
24 Specify update interval. The command will not allow quicker
25 than 0.1 second interval, in which the smaller values are con‐
26 verted. Both '.' and ',' work for any locales. The WATCH_INTER‐
27 VAL environment can be used to persistently set a non-default
28 interval (following the same rules and formatting).
29 -p, --precise
31 Make watch attempt to run command every --interval seconds. Try
32 it with ntptime (if present) and notice how the fractional sec‐
33 onds stays (nearly) the same, as opposed to normal mode where
34 they continuously increase.
35 -t, --no-title
37 Turn off the header showing the interval, command, and current
38 time at the top of the display, as well as the following blank
39 line.
40 -b, --beep
42 Beep if command has a non-zero exit.
43 -e, --errexit
45 Freeze updates on command error, and exit after a key press.
46 -g, --chgexit
48 Exit when the output of command changes.
49 -c, --color
51 Interpret ANSI color and style sequences.
52 -x, --exec
54 Pass command to exec(2) instead of sh -c which reduces the need
55 to use extra quoting to get the desired effect.
56 -w, --no-linewrap
58 Turn off line wrapping. Long lines will be truncated instead of
59 wrapped to the next line.
60 -h, --help
62 Display help text and exit.
63 -v, --version
65 Display version information and exit.
66
68 0 Success.
69 1 Various failures.
70 2 Forking the process to watch failed.
71 3 Replacing child process stdout with write side pipe
72 failed.
73 4 Command execution failed.
74 5 Closing child process write pipe failed.
75 7 IPC pipe creation failed.
76 8 Getting child process return value with waitpid(2)
77 failed, or command exited up on error.
78 other The watch will propagate command exit status as child
79 exit status.
81 The behaviour of watch is affected by the following environment vari‐
82 ables.
83 WATCH_INTERVAL
85 Update interval, follows the same rules as the --interval com‐
86 mand line option.
88 POSIX option processing is used (i.e., option processing stops at the
89 first non-option argument). This means that flags after command don't
90 get interpreted by watch itself.
92 Upon terminal resize, the screen will not be correctly repainted until
93 the next scheduled update. All --differences highlighting is lost on
94 that update as well.
95 Non-printing characters are stripped from program output. Use cat -v
97 as part of the command pipeline if you want to see them.
98 Combining Characters that are supposed to display on the character at
100 the last column on the screen may display one column early, or they may
101 not display at all.
102 Combining Characters never count as different in --differences mode.
104 Only the base character counts.
105 Blank lines directly after a line which ends in the last column do not
107 display.
108 --precise mode doesn't yet have advanced temporal distortion technology
110 to compensate for a command that takes more than --interval seconds to
111 execute. watch also can get into a state where it rapid-fires as many
112 executions of command as it can to catch up from a previous executions
113 running longer than --interval (for example, netstat taking ages on a
114 DNS lookup).
116 To watch for mail, you might do
117 watch -n 60 from
118 To watch the contents of a directory change, you could use
119 watch -d ls -l
120 If you're only interested in files owned by user joe, you might use
121 watch -d 'ls -l | fgrep joe'
122 To see the effects of quoting, try these out
123 watch echo $$
124 watch echo '$$'
125 watch echo "'"'$$'"'"
126 To see the effect of precision time keeping, try adding -p to
127 watch -n 10 sleep 1
128 You can watch for your administrator to install the latest kernel with
129 watch uname -r
130 (Note that -p isn't guaranteed to work across reboots, especially in
131 the face of ntpdate (if present) or other bootup time-changing mecha‐
132 nisms)
133procps-ng 2020-12-06 WATCH(1)