C command-line password input

Question

I want to allow users to enter password using command-line interface. but I don\'t want to display this password on screen (or display \"****\").

How to do it in C?

Answer 1

To do this in a portable way you will need to use a standardized or de-facto standard library.

See man 3 termios and man 3 ncurses.

Here is a program that will work on Linux and other Unix systems...

#include 

int main(void) {
  int f = open("/dev/tty", 0);
  char s[100];

  system("stty -echo > /dev/tty");
  f >= 0 && read(f, s, sizeof s) > 0 &&  printf("password was %s", s);
  system("stty echo > /dev/tty");
  return 0;
}

A number of improvements are possible. Using termios would probably be better, and it would avoid the fork and possible security issues of system(). Using standard I/O to read the password would probably be better. (As written the typed newline would have to be deleted.) There is a getpass() function in Linux and some others however it is marked as "obsolete. Do not use it.". It might be a good idea to deal with SIGTSTP.

Overall, I might look for an existing solution that deals with all these little issues...