grepcidr 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. grepcidr is capable
of comparing thousands or even millions of IPs to
networks with little memory usage and in
reasonable computation time. It has endless uses
in network software, including mail filtering and
processing, network security, log analysis, and
many custom applications.
