filter files for IP address matches
grepcidr3 can be used to filter a list of IP addresses against one or more Classless Inter-Domain Routing (CIDR) specifications, or arbitrary networks specified by an address range. As with grep, there are options to invert matching and load patterns from a file. grepcidr3 is capable of comparing thousands or even millions of IPs to networks with little memory usage and in reasonable computation time. grepcidr3 has endless uses in network software, including: mail filtering and processing, network security, log analysis, and many custom applications.
Homepage: https://github.com/jrlevine/grepcidr3