termios/echo_off.c

   1 /* compile with:
   2    gcc echo_off -o echo_off -Wall -W -Wextra -ansi -pedantic
   3
   4    Whenever a user types in a password, it is desirable that
   5    the password itself doesn't show up at all. To implement
   6    such behaviour, we use the termios(4) interface to disable
   7    echo'ing.
   8 */
   9
  10 #include <fcntl.h>
  11 #include <stdio.h>
  12 #include <stdlib.h>
  13 #include <termios.h>
  14
  15 #define PASSLEN 64
  16
  17 /* function prototypes */
  18 void diep(const char *s);
  19
  20 int main(int argc, char *argv[])
  21 {
  22     struct termios oldt, newt;
  23     char password[PASSLEN];
  24     int fd;
  25
  26     /* check argument count */
  27     if (argc != 2) {
  28         fprintf(stderr, "Usage: %s tty\n", argv[0]);
  29         exit(EXIT_FAILURE);
  30     }
  31
  32     /* open terminal device */
  33     if ((fd = open(argv[1], O_RDONLY | O_NOCTTY) == -1))
  34         diep("open");
  35
  36     /* get current termios structure */
  37     if (tcgetattr(fd, &oldt) == -1)
  38         diep("tcgetattr");
  39
  40     /* set new termios structure */
  41     newt = oldt;
  42     newt.c_lflag &= ~ECHO;     /* disable echoing */
  43     newt.c_lflag |= ECHONL;    /* echo NL even if ECHO is off */
  44
  45     if (tcsetattr(fd, TCSANOW, &newt) == -1)
  46         diep("tcsetattr");
  47
  48     /* prompt for password and get it */
  49     printf("Password: ");
  50     fgets(password, PASSLEN, stdin);
  51
  52     /* restore old termios structure */
  53     if (tcsetattr(fd, TCSANOW, &oldt) == -1)
  54         diep("tcsetattr");
  55
  56     return EXIT_SUCCESS;
  57 }
  58
  59 void diep(const char *s)
  60 {
  61     perror(s);
  62     exit(EXIT_FAILURE);
  63 }