pcapcompile

pcapcompile is a small tool in the tcpdump/libpcap ecosystem designed to translate a textual filter expression into a compiled BPF program. It is typically used for development, testing, or educational purposes to verify that a filter will compile and to inspect the resulting BPF bytecode.

It relies on the same internal library function pcap_compile, which parses expressions like "tcp port 80" or "ip and not 10.0.0.1" and translates them into BPF instructions. The tool can be configured for different link-layer types and network masks to reflect targeting conditions.

Typical usage involves invoking the program with a filter string and, optionally, a specified data-link type and netmask. The output usually includes either a success indication and the number of BPF instructions, or an error with a diagnostic message. It is primarily a debugging aid rather than a general-purpose packet capture tool.

In practice, developers integrate pcapcompile into workflows to ensure filter correctness before deployment in a capture program such as tcpdump or libpcap-based apps. The tool's behavior and options can vary across versions, and up-to-date documentation is available in the corresponding libpcap release notes or manual pages.

See also: libpcap, pcap_compile, BPF, tcpdump.