nmapgrep is a small tool customized to grep regular expression patterns from a nmap log file and output the IP addresses that match the pattern.
You can download it from the following link: https://packetstormsecurity.com/files/download/33404/nmapgrep-0.2.c
Source: https://packetstormsecurity.com/files/33404/nmapgrep-0.2.c.html