child_std_fd      101 popen.cpp          int child_std_fd = do_read ? STDOUT_FILENO : STDIN_FILENO;
child_std_fd      103 popen.cpp          if (child_fd != child_std_fd) {
child_std_fd      104 popen.cpp            dup2(child_fd, child_std_fd);
child_std_fd      116 popen.cpp            if (fd != child_std_fd) {
child_std_fd      122 popen.cpp          fcntl(child_std_fd, F_SETFD, 0);