ngrep strives to provide most of GNU grep's common features, applying
them to the network layer.

ngrep a pcap-aware tool that will allow you to specify extended
regular expressions to match against data payloads of packets. It
currently recognizes TCP and UDP across Ethernet, PPP and SLIP
interfaces, and understands BPF filter logic in the same fashion
as more common packet sniffing tools, like tcpdump and snoop.