program to monitor files

[Russell Coker <russell@coker.com.au>]

I am after a program that will monitor a file (like a log file) and then when
some data is added to it, a program should be run.

For example I have a file that I want printed, so whenever there's some new
data added to the end of the file and after there has been ~20 seconds of no
change (I don't want this happening once per second for 20 seconds) I want
the data to be piped into "lpr".

Is there any program in Debian that can do this?

I could write something myself in a couple of hours but it would be easier to
use someone else's program.

-- 
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it, and to take delight in it is far better than simply being fond of it.