int
main(int argc, char **argv) {
	static char buf[COM_BUF_SIZE];
	while(1) {
                memset(buf, 0, sizeof(buf));
printf("   > ");
char *com = fgets(buf, sizeof(buf), stdin);
                for (int i = 0; i < sizeof(buf); i++)
                        if (buf[i] == '\n')    
                                buf[i] = '\0';
		if (com != NULL) {
                        if (commands[com[0]] != NULL) commands[com[0]](buf);
                        else puts("invalid command.");
                }
        }
        return 0;
}