ngrep strives to provide most of GNU grep's common features, applying them
to the network layer. ngrep is a pcap-aware tool that will allow you to
specify extended regular or hexadecimal expressions to match against data
payloads of packets. It currently recognizes IPv4/6, TCP, UDP, ICMPv4/6,
IGMP and Raw across Ethernet, PPP, SLIP, FDDI, Token Ring and null interfaces,
and understands BPF filter logic in the same fashion as more common packet
sniffing tools, such as tcpdump and snoop.