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 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.
WWW: http://ngrep.sourceforge.net/
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