Update: While reporting this issue to Pexpect: https://github.com/pexpect/pexpect/issues/662 , I found that their own implementation _fork_pty.fork_pty() for Solaris also works on macOS, due to explicit opening /dev/tty in the child process: 		if (pid == 0) {	// child 				int ttyfd = open("/dev/tty", O_WRONLY); 				CHECK(ttyfd != -1); 				CHECK(close(ttyfd) != -1); [...] after that (with these 3 lines added after line #26), the output on macOS is: $ ./a.out read 64 bytes: 0123456789012345678901234567890123456789012345678901234567890123 read 36 bytes: 456789012345678901234567890123456789 read 0 bytes: