Ngrep

Ngrep is a tool that provides GNU grep's features applying them to the network layer.

Overview

Ngrep recognizes IPv4/6, TCP, UDP, ICMPv4/6, IGMP and Raw across Ethernet, PPP, SLIP, FDDI, Token Ring and null interfaces.

Example 1: dump all common HTTP requests on a live network (eth0):

ngrep -qd eth0 '^(GET|POST|HEAD|CONNECT)' 'tcp'

Example 2: the same, but from a network dump (out.pcap):

ngrep -qI out.pcap '^(GET|POST|HEAD|CONNECT)' 'tcp'

Ngrep cannot reconstruct data streams, it has no ability to match a string that is broken across two or more packets.