huschi.net

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 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.
       -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
              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      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.
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@
       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)