pflang—Packet Filter Language introduced by tcpdump/libpcap
uses a small domain-specific language (DSL) to specify which part of the traffic the user is interested in, in the form of a packet filter.
In the decades since, many other tools have adopted that language, often extending it somewhat. This DSL is also known under the name Berkeley Packet Filter
- pflua, which generates high-performance packet filters by compiling pflang to Lua and then compiling that using the LuaJIT just-in-time compiler
- NFDUMP/NfSen uses a variant of pflang to filter flows rather than packets
- Wireshark (also has its own different filter language)
- and many others...