Many years ago (when the dinosaurs were using V6), I had a crazy idea[*] that a write(fd, 0, NULL) would somehow signal EOF to the reader i.e. a subsequent read would wait for further data instead of ENOTOBACCO. Did any *nix ever implement that? I have no idea how it would be done. Have an ENOGORILLA. To answer the real question: stream pipes, which became the only sort of pipe in the Research stream (sic) sometime between the 8/e and 9/e manuals. The implementation was trivial, because from the beginning the metadata within a stream admitted delimiters: markers that meant `when this object reaches read(2) at the head end, return from read with whatever has already been delivered.' Empty messages (two consecutive delimiters) were explicitly allowed. If a stream was marked as using delimeters (and pipes always were), a delimeter was inserted after every write(2). So write(2) generated an empty message, and read(2) returned it. Norman Wilson Toronto ON