int mainfd=0;
char ch[2] = {NULL};
 
void *write(void *)
{
    char temp;
    while(1)
    {
        temp = getchar();
        ch[0] = temp;   ch[1] = '\0';
        if(temp == '~')
        {
            printf("connection closed.\r\n");
            close(mainfd);
            pthread_exit(NULL);
        }
        check=write(mainfd, ch, 1);
        ch[0]='\0';
    }
}
 
void *read(void *)
{
    char outputbuffer[10000]= {0};
    while(1)
    {
                outputbuffer[0]='\0';
                int charnumber=read(mainfd, &outputbuffer, sizeof(outputbuffer));
                outputbuffer[charnumber] = '\0';
                printf("%s",outputbuffer);
                outputbuffer[0] = '\0';
    }
}
 
int main(int argc,char *argv[])
{
    //////////////////
    struct termios old = {0};
    if (tcgetattr(0, &old) < 0)
        perror("tcsetattr()");
    old.c_lflag &= ~ICANON;
    old.c_lflag &= ~ECHO;
    old.c_cc[VMIN] = 1;
    old.c_cc[VTIME] = 0;
    if (tcsetattr(0, TCSANOW, &old) < 0)
         perror("tcsetattr ICANON");
    //////////////////
    struct termios options;
    static int portnum=atoi(argv[1]);
 
    mainfd = open_port(portnum);
 
    fcntl(mainfd, F_SETFL, FNDELAY);  
    tcgetattr(mainfd, &options);
    cfsetspeed(&options, speed);
    options.c_cflag |= (CLOCAL | CREAD);
    options.c_cflag &= ~PARENB;
    options.c_cflag |= CSTOPB;
 
    options.c_cflag &= ~CSIZE;
    options.c_cflag |=  CS8;
    options.c_cflag &= ~CRTSCTS;
    options.c_iflag &= ~(ISTRIP|ICRNL);
    options.c_oflag &= ~OPOST;
    options.c_lflag &= ~(ICANON|ISIG|IEXTEN|ECHO);
    options.c_cc[VMIN] = 1;
    options.c_cc[VTIME] = 0;
    //
    tcsetattr(mainfd, TCSAFLUSH, &options);
    pthread_t threads[2];
    pthread_create(&threads[0], NULL, write, NULL);
    pthread_create(&threads[1], NULL, read, NULL);
    pthread_exit(NULL);
}

Router>
Router>abc // While I typed "abcd". If I continue with typing "e", then the output will be "abcd" and so on ...