watch

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 perma-
              nent, 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 interval, in which the smaller values  are  con-
              verted. Both '.' and ',' work for any locales.

       -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 continu-
              ously 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.

       -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 argument).  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 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
       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)