Shell on a pty

pty_login.c

#include <stdio.h>
#include <stdlib.h>
#include <pty.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <sys/select.h>

#define BUF_SIZE 80

int main () {
    int pty, nbytes;
    fd_set des_set;
    char buf[BUF_SIZE];
    struct termios attr;

    pid_t pid = forkpty(&pty, NULL, NULL, NULL);
    switch(pid) {
    case -1:
        perror("forkpty");
        exit(EXIT_FAILURE);
        break;
    case 0:
        execlp("/bin/login", "/bin/login", NULL);
        perror("exelp");
        exit(EXIT_FAILURE);
        break;
    default:
        /* turn off echo and canonical mode */
        tcgetattr(STDIN_FILENO, &attr);
        attr.c_lflag &= ~(ECHO|ICANON);
        attr.c_cc[VTIME] = 0;
        attr.c_cc[VMIN] = 0;
        tcsetattr(STDIN_FILENO, TCSANOW, &attr);

        while (1) {
            FD_ZERO (&des_set);
            FD_SET (pty, &des_set);
            FD_SET (STDIN_FILENO, &des_set);
            if (select (FD_SETSIZE, &des_set, NULL, NULL, NULL) < 0)
                {
                    perror ("select");
                    exit (EXIT_FAILURE);
                }
            /* from stdin to pty */
            if (FD_ISSET (STDIN_FILENO, &des_set))
                {
                    nbytes = read(STDIN_FILENO, buf, BUF_SIZE);
                    if (nbytes > 0)
                        write(pty, buf, nbytes);
                    else if (nbytes < 0)
                        exit(EXIT_FAILURE);
                }
            /* from pty to stdout */
            if (FD_ISSET (pty, &des_set))
                {
                    nbytes = read(pty, buf, BUF_SIZE);
                    if (nbytes > 0)
                        write(STDOUT_FILENO, buf, nbytes);
                    else if (nbytes < 0)
                        exit(EXIT_FAILURE);
                }
        }
        close(pty);
        break;
    }
    return 0;
}