glibc/manual/examples/db.c

/* User and Group Database Example
   Copyright (C) 1991-2020 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 2
   of the License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, see <https://www.gnu.org/licenses/>.
*/

#include <grp.h>
#include <pwd.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>

int
main (void)
{
  uid_t me;
  struct passwd *my_passwd;
  struct group *my_group;
  char **members;

  /* Get information about the user ID. */
  me = getuid ();
  my_passwd = getpwuid (me);
  if (!my_passwd)
    {
      printf ("Couldn't find out about user %d.\n", (int) me);
      exit (EXIT_FAILURE);
    }

  /* Print the information. */
  printf ("I am %s.\n", my_passwd->pw_gecos);
  printf ("My login name is %s.\n", my_passwd->pw_name);
  printf ("My uid is %d.\n", (int) (my_passwd->pw_uid));
  printf ("My home directory is %s.\n", my_passwd->pw_dir);
  printf ("My default shell is %s.\n", my_passwd->pw_shell);

  /* Get information about the default group ID. */
  my_group = getgrgid (my_passwd->pw_gid);
  if (!my_group)
    {
      printf ("Couldn't find out about group %d.\n",
	      (int) my_passwd->pw_gid);
      exit (EXIT_FAILURE);
    }

  /* Print the information. */
  printf ("My default group is %s (%d).\n",
	  my_group->gr_name, (int) (my_passwd->pw_gid));
  printf ("The members of this group are:\n");
  members = my_group->gr_mem;
  while (*members)
    {
      printf ("  %s\n", *(members));
      members++;
    }

  return EXIT_SUCCESS;
}