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WATCH


Section: Linux User’s Manual (1)
Updated: 1999 Apr 3
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NAME

watch – execute a program periodically, showing output fullscreen
 

SYNOPSIS

watch

[-dhvt] [-n <seconds>] [–differences[=cumulative]] [--help] [--interval=<seconds>] [--no-title] [--version] <command>

 

DESCRIPTION

watch

runs
command

repeatedly, displaying its output (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.

The
-d

or
–differences

flag will highlight the differences between successive updates. The
–cumulative

option 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.

watch

will run until interrupted.
 

NOTE

Note that
command

is given to "sh -c"
which means that you may need to use extra quoting to get the desired effect.

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 "’"’$$’"’"

You can watch for your administrator to install the latest kernel with



watch uname -r

(Just kidding.)
 

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.
 

AUTHORS

The original
watch

was written by Tony Rems <[email protected]> in 1991, with mods and
corrections by Francois Pinard. It was reworked and new features added by
Mike Coleman <[email protected]> in 1999.



 

Index



NAME

SYNOPSIS

DESCRIPTION

NOTE

EXAMPLES

BUGS

AUTHORS



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