2002-02-02 04:17:29 +05:30
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.TH WATCH 1 "1999 Apr 3" " " "Linux User's Manual"
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.SH NAME
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watch \- execute a program periodically, showing output fullscreen
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.SH SYNOPSIS
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.B watch
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2003-02-09 12:57:16 +05:30
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.I [\-dhvt] [\-n <seconds>] [\-\-differences[=cumulative]] [\-\-help] [\-\-interval=<seconds>] [\-\-no\-title] [\-\-version] <command>
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2002-02-02 04:17:29 +05:30
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.SH DESCRIPTION
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.BR watch
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runs
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.I command
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repeatedly, displaying its output (the first screenfull). This allows you to
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watch the program output change over time. By default, the program is run
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every 2 seconds; use
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.I -n
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or
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.I --interval
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to specify a different interval.
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.PP
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The
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.I -d
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or
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.I --differences
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flag will highlight the differences between successive updates. The
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.I --cumulative
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option makes highlighting "sticky", presenting a running display of all
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2003-02-09 12:57:16 +05:30
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positions that have ever changed. The
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.I -t
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or
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.I --no-title
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option turns off the header showing the interval, command, and current
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time at the top of the display, as well as the following blank line.
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2002-02-02 04:17:29 +05:30
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.PP
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.BR watch
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will run until interrupted.
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.SH NOTE
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Note that
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.I command
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is given to "sh -c"
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which means that you may need to use extra quoting to get the desired effect.
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.PP
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Note that POSIX option processing is used (i.e., option processing stops at
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the first non-option argument). This means that flags after
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.I command
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don't get interpreted by
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.BR watch
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itself.
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.SH EXAMPLES
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.PP
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To watch for mail, you might do
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.IP
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watch \-n 60 from
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.PP
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To watch the contents of a directory change, you could use
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.IP
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watch \-d ls \-l
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.PP
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If you're only interested in files owned by user joe, you might use
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.IP
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watch \-d 'ls \-l | fgrep joe'
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.PP
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To see the effects of quoting, try these out
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.IP
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watch echo $$
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.IP
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watch echo '$$'
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.IP
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watch echo "'"'$$'"'"
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.PP
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You can watch for your administrator to install the latest kernel with
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.IP
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watch uname -r
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.PP
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(Just kidding.)
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.SH BUGS
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Upon terminal resize, the screen will not be correctly repainted until the
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next scheduled update. All
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.I --differences
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highlighting is lost on that update as well.
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.PP
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Non-printing characters are stripped from program output. Use "cat -v" as
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part of the command pipeline if you want to see them.
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.SH AUTHORS
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The original
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.B watch
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was written by Tony Rems <rembo@unisoft.com> in 1991, with mods and
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corrections by Francois Pinard. It was reworked and new features added by
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Mike Coleman <mkc@acm.org> in 1999.
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