"Tailing" grep

[Adam Funk]

On 2007-09-30, Brian Fahrlander wrote:

>      While we've got the attention of the most-able on this subject, I'd 
> like to reopen a discussion about a very similar tool: a 'grep' that 
> happens on tailing a file.  There have been dozens of times that I'm 
> looking for a message number in /var/log/mail.log and would love to see 
> only the lines mentioning that message.
>
>      A couple of years ago I asked and got a "maybe you could write 
> something", but I actually never could.  It's not as easy as it looks.
>
>      Any chance you guys have seen this done?

If you're interested in doing this within a script called by cron or
at, you might want to look at the logtail package (which is used by
logcheck).  

Basically it stores (in a configurable file) the line number it last
read, and when called again gets the lines after that and updates the
marker.