Determine the size of a pipe without calling read()

Question

I need a function called SizeOfPipe() which should return the size of a pipe - I only want to know how much data is in the pipe and not actually read data off t

Answer 1

Unfortunately the system cannot always know the size of a pipe - for example if you are piping a long-running process into another command, the source process may not have finished running yet. In this case there is no possible way (even in theory) to know how much more data is going to come out of it.

If you want to know the amount of data currently available to read out of the pipe that might be possible, but it will depend on OS buffering and other factors which are hard to control. The most common approach here is just to keep reading until there's nothing left to come (if you don't get an EOF then the source process hasn't finished yet). However I don't think this is what you are looking for.

So I'm afraid there is no general solution.