I found a host where I was getting a bunch of POST's in my apache server log files which looked to be malicious. I wanted to go through and just block all IP's which were trying to post to my web server, since I don't have anything but static content on it. So, I came up with this little one liner:
grep POST /var/log/apache2/*log* | perl -lane 'print $1 if (/^.*?:(.*?)\s/)'|sort | uniq | perl -lane 'system "iptables -A INPUT -s @F -j DROP"'
This is useful for any group of IP's you wish to black-hole.