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 interval, 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 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).

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@unisoft.com⟩ in 1991, with  mods  and  corrections  by
       Francois Pinard.  It was reworked and new features added by Mike Coleman ⟨mkc@acm.org⟩ in 1999. The beep,
       exec, and error handling features were added by Morty Abzug ⟨morty@frakir.org⟩ in 2008.  On a not so dark
       and  stormy  morning  in  March of 2003, Anthony DeRobertis ⟨asd@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@rrod.net⟩