It's a shame that stdX streams were never spec'd as sockets, with appropriate handling available in the various shells.
Also, file handle inheritance by default was such a big mistake.
Also, file handle inheritance by default was such a big mistake.
Working dir, env vars, uid/gid, socket handles, file descriptors, (some) file locks, message queues. AFAIK the only exception is the argv, everything else is inherited on fork or exec.
Sometimes this makes sense, but programmers always forget about this, resulting in security incidents. Eventually most programming languages gave up and updated their stdlibs to set CLOEXEC when opening files and sockets, knowing that it would break POSIX compatibility and API compatibility on their stdlibs. Python is one example: https://peps.python.org/pep-0446/
The "inherit by default" behavior also makes it very difficult to evolve the shell interface. The nushell devs are looking for a reliable way to request JSON output/input on processes spawned by the shell (if supported by the program). Naively passing env vars or FDs to the process causes problems because if the process spawns any children of it's own, they too would also inherit those env vars or FDs.
The initial design used fd3 but, as this thread demonstrates, that risked breaking more things.
The next design was using BSD sockets. But that has cross platform implications.
environment (in a broader sense, not just environment variables, but also CWD, file handles, uid/gid, sec context, namespaces) is there for a reason: to use. if you dont want your children processes to read the stdin in place of you, dont give it to them. it's the parent process responsibility to set up the env for the children.
although subprocesses are invented to do (some of) the parent's job by delegating smaller steps and leave the details to them. for example a http server would read the request (first) line, then delegate the rest of the input to a subprocess (worker) depending on who is free, who handles which type of request, etc. this is original idea behind inheritance, IMO.