termios/echo_off.c

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