In the RTL reference (RTL.pdf, 2021) under the topic "BaseUnix' on page 207, there is an article on function "FpPipe." There is an example program there illustrating the function's use, but the example code never actually uses the function FpPipe(var fildes: TFilDes) : cint. It does use the function assignpipe which is in fact and in turn described (with the same example program) under the RTL reference topic "Unix" on page 2078.
This is a little confusing, so I set out to find the source for either of these functions in /fpcsrc/rtl thinking that would help clarify things, but I've had no luck. Can anyone tell me where I need to look?