watch(1) - phpMan

WATCH(1)                                  User Commands                                  WATCH(1)

NAME
       watch - execute a program periodically, showing output fullscreen

SYNOPSIS
       watch [options] command

DESCRIPTION
       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
       -d, --differences [permanent]
              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.

       -n, --interval seconds
              Specify update interval.  The command will not allow quicker than 0.1 second inter-
              val, in which the smaller values are converted. Both '.' and ',' work for  any  lo-
              cales.

       -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 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  quot-
              ing to get the desired effect.

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

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

EXIT STATUS
              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.
NOTES
       POSIX option processing is used (i.e., option processing stops at the first non-option ar-
       gument).  This means that flags after command don't get interpreted by watch itself.
BUGS
       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  char-
       acter 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 pre-
       vious executions running longer than interval (for example, netstat taking ages on  a  DNS
       lookup).
EXAMPLES
       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
       or other bootup time-changing mechanisms)

procps-ng                                   2018-03-03                                   WATCH(1)

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