"A language written by the old Unix hands", e.g. C or awk. Thus a language cowritten by Pike and Thompson certainly counts. ;}}}}
(Nice language, in general, if very embryonic so far. I'm amazed they reintroduced the ; as a statement *separator* mistake from the Pascal lineage: they have rules allowing optional ;s everywhere, so you can *treat* it like a statement terminator, but still this decision is the only one that stands out as outright bizarre.)