watch(1) — Linux manual page


WATCH(1)                        User Commands                       WATCH(1)

NAME         top

       watch - execute a program periodically, showing output fullscreen

SYNOPSIS         top

       watch [options] command

DESCRIPTION         top

       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, command is run every 2 seconds and
       watch will run until interrupted.

OPTIONS         top

       -d, --differences[=permanent]
              Highlight the differences between successive updates. If the
              optional =permanent argument is specified then watch will show
              all changes since the 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. Both '.' and ',' work for any locales. The
              WATCH_INTERVAL environment can be used to persistently set a
              non-default interval (following the same rules and

       -p, --precise
              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.

       -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

       -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 command changes.

       -c, --color
              Interpret ANSI color and style sequences.

       -x, --exec
              Pass command to exec(2) instead of sh -c which reduces the
              need to use extra quoting to get the desired effect.

       -h, --help
              Display help text and exit.

       -v, --version
              Display version information and exit.

EXIT STATUS         top

              0      Success.
              1      Various failures.
              2      Forking the process to watch failed.
              3      Replacing child process stdout with write side pipe
              4      Command execution failed.
              5      Closing 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.

ENVIRONMENT         top

       The behaviour of watch is affected by the following environment

              Update interval, follows the same rules as the --interval
              command line option.

NOTES         top

       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 itself.

BUGS         top

       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 character counts.

       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
       previous executions running longer than interval (for example,
       netstat taking ages on a DNS lookup).

EXAMPLES         top

       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
              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)

COLOPHON         top

       This page is part of the procps-ng (/proc filesystem utilities)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2020-06-09.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-06-04.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to

procps-ng                        2020-06-04                         WATCH(1)