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[=cumu‐

       lative]] [--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

       seconds 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 com‐

       mand 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 executions

       running longer than interval (for example, netstat taking ages on a DNS

       lookup).