WATCH(1)							Linux User's Manual							  WATCH(1)

NAME

       watch - execute a program periodically, showing output fullscreen

SYNOPSIS

       watch [-bdehpvtx] [-n seconds] [--beep] [--color] [--differences[=cumulative]] [--errexit] [--exec] [--help] [--interval=seconds]
       [--no-title] [--precise] [--version] 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; use -n or --interval to specify a different interval. Normally, this interval
       is interpreted as the amout of time between the completion of one run of command and the beginning of the next run. However, with the -p or
       --precise option, you can make watch attempt to run command every interval seconds. Try it with ntptime and notice how the fractional sec-
       onds stays (nearly) the same, as opposed to normal mode where they continuously increase.

       The -d or --differences flag will highlight the differences between successive updates.	Using --differences=cumulative makes highlighting
       "sticky", presenting a running display of all positions that have ever changed.	The -t or --no-title option turns off the header showing
       the interval, command, and current time at the top of the display, as well as the following blank line.	The -b or --beep option causes the
       command to beep if it has a non-zero exit.

       watch will normally run until interrupted. If you want watch to exit on an error from the program running use the -e or --errexit options,
       which will cause watch to exit if the return value from the program is non-zero.

       By default watch will normally not pass escape characters, however if you use the --c or --color option, then watch will interpret ANSI
       color sequences for the foreground.

NOTE

       Note that command is given to "sh -c" which means that you may need to use extra quoting to get the desired effect.  You can disable this
       with the -x or --exec option, which passes the command to exec(2) instead.

       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 exe-
       cutions running longer than interval (for example, netstat taking ages on a DNS lookup).

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.  Uni-
       code support was added in 2009 by Jarrod Lowe <procps@rrod.net>.

								    2010 Mar 01 							  WATCH(1)