tcpick is a textmode sniffer that can track tcp streams and saves the data captured in files or displays them in the terminal. Useful for picking files in a passive way.
It can store all connections in different files, or it can display all the stream on the terminal. It is useful to keep track of what users of a network are doing, and is usable with textmode tools like grep, sed and awk. It can handle eth and ppp interfaces.