[dllthomas]

I'm pretty sure popen is just a wrapper around this stuff. It's basically,

pipe: get two fds connected by a pipe

fork: create a child process

dup2: move the read fd of the pipe to 0 (stdin) in the new process

exec: run the program in the child process

There's some cleanup but that's the gist - popen isn't a syscall (or reasonably close to one), so must necessarily rely on other stuff to get its work done where it actually interfaces with the kernel.

[wethesheeple]

That makes perfect sense. It's the fork+exec that makes it dangerous (e.g. in the CGI context). This is something I've been wondering about and you have just provided a jolt of clarity. Many thanks, again.

[dllthomas]

Happy to help :)