[Exim] Sed Regex help

I'm a little slow that this so I can use the help of someone smarter
than me.

I'm needing to write a script so that if someone hits a specific web
page - it locks out their IP address. I have part of it written. So this
should be simple. The IP address is the first field in the lines that
I'm looking at.

So I'm going to run:

tail -f logfile|grep webpage| something | blockip <the ip address>

So - the "something" has to cut out the IP address for the lines coming
through and run blockip with the ip adress as the parameter.

I have a hacker problem and I think I can trap him with this.

So - thanks in advance for your help.