The whole point of a pipe is to have concurrent input and output. If so, and if you open the same file for input and output, you risk erasing the file by openin

The whole point of a pipe is to have concurrent input and output. If so, and if you open the same file for input and output, you risk erasing the file by opening and deleting the file on the output side before reading it on the input side. If the pipe is an unfulfilled promise (no concurrency) then there's no problem. But if the pipe does what it's designed to do, you will lose the file.