gistfile1.h

	// We don't actually execute the command given in prog, as we don't want 
	// to have to split it up into its individual components. Instead, we execute
	// all of its components as an argument to /bin/sh -c.
	char *spawnedArgs[] = {(char*)_PATH_BSHELL, "-c", (char*)RSTRING_PTR(prog), NULL};
	posix_spawn_file_actions_t actions;
	
	if ((pipe(read_pipe) < 0) || (pipe(write_pipe) < 0)) {
		posix_spawn_file_actions_destroy(&actions);
		rb_sys_fail("pipe() failed.");
	}
	
	
	#define STREAM_OUTPUT  read_pipe[0]
	#define PROCESS_OUTPUT   read_pipe[1]
	
	#define STREAM_INPUT write_pipe[1]
	#define PROCESS_INPUT   write_pipe[0]

	
	rb_sys_fail_unless(posix_spawn_file_actions_init(&actions), "could not init file actions");
	rb_sys_fail_unless(posix_spawn_file_actions_adddup2(&actions, PROCESS_OUTPUT, STDOUT_FILENO), 
		"could not add dup2() to stdout");
	rb_sys_fail_unless(posix_spawn_file_actions_addclose(&actions, PROCESS_OUTPUT), "");
	errno = posix_spawn(&pid, spawnedArgs[0], &actions, NULL, spawnedArgs, *(_NSGetEnviron()));
	if(errno != 0) {
		int err = errno;
		close(write_pipe[0]);
		close(write_pipe[1]);
		errno = err;
		rb_sys_fail("posix_spawn failed.");
	}
	posix_spawn_file_actions_destroy(&actions);
	
	if (convert_mode_string_to_fmode(mode) != FMODE_WRITABLE) {
		// the mode was either 'r', 'r+', or 'w+', so make a read stream.
		r = _CFReadStreamCreateFromFileDescriptor(NULL, PROCESS_INPUT);
		if (r != NULL) {
			CFReadStreamOpen(r); 
			CFMakeCollectable(r);
			GC_WB(&io_struct->readStream, r);
		}
	}
	
	if (convert_mode_string_to_fmode(mode) != FMODE_READABLE) {
		// the mode was either 'r+', 'w', or 'w+', so make a write stream.
		w = _CFWriteStreamCreateFromFileDescriptor(NULL, PROCESS_OUTPUT);
		if (w != NULL) {
			CFWriteStreamOpen(w);
			CFMakeCollectable(w);
			GC_WB(&io_struct->writeStream, w);
    	} else {
			printf("oh god, things didn't work...");
		}
	}
	
    // TODO: Eventually make the ungetc_buf a ByteString
	io_struct->fd = PROCESS_OUTPUT;
	io_struct->pipe = read_pipe[1];
    io_struct->ungetc_buf = NULL;
    io_struct->ungetc_buf_len = 0;
    io_struct->ungetc_buf_pos = 0;
	io_struct->pid = pid;
    io_struct->sync = 0;
	
    rb_objc_keep_for_exit_finalize((VALUE)io);
    return io;