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. 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

              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

       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

       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
       (if present) or other bootup time-changing mechanisms)