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, the program  is
       run every 2 seconds.  By default, 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.

       -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 sequences.

       -x, --exec
              command is given to sh -c which means that you may need to use extra quoting to get
              the desired effect.  This with the --exec  option,  which  passes  the  command  to
              exec(2) instead.

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

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

NOTE
       Note  that  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.

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)

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).

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      Closign 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.
AUTHORS
       The  original  watch  was  written by Tony Rems ⟨rembo AT unisoft.com⟩ in 1991, with mods and
       corrections by Francois Pinard.  It was reworked and new features added  by  Mike  Coleman
       ⟨mkc AT acm.org⟩  in  1999.  The  beep, exec, and error handling features were added by Morty
       Abzug ⟨morty AT frakir.org⟩ in 2008.  On a not so dark and stormy morning in March  of  2003,
       Anthony  DeRobertis ⟨asd AT suespammers.org⟩ got sick of his watches that should update every
       minute eventually updating many seconds after the minute started,  and  added  microsecond
       precision.  Unicode support was added in 2009 by Jarrod Lowe ⟨procps AT rrod.net⟩



procps-ng                                   June 2011                                    WATCH(1)