watch(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | ENVIRONMENT | NOTES | BUGS | EXAMPLES | COLOPHON

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 formatting).

       -p, --precise
              Make watch attempt to run command every --interval
              seconds.  Try it with ntptime (if present) 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 line.

       -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.

       -w, --no-linewrap
              Turn off line wrapping. Long lines will be truncated
              instead of wrapped to the next line.

       -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
                     failed.
              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
       variables.

       WATCH_INTERVAL
              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
       with
              watch uname -r
       (Note that -p isn't guaranteed to work across reboots, especially
       in the face of ntpdate (if present) 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 
       ⟨https://gitlab.com/procps-ng/procps⟩.  If you have a bug report
       for this manual page, see
       ⟨https://gitlab.com/procps-ng/procps/blob/master/Documentation/bugs.md⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://gitlab.com/procps-ng/procps.git⟩ on 2021-08-27.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-08-24.)  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
       man-pages@man7.org

procps-ng                      2020-12-06                       WATCH(1)

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