text: /* GNU's users.
     Copyright (C) 1992-2015 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 3 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 <http://www.gnu.org/licenses/>.  */
  
  /* Written by jla; revised by djm */
  
  #include <config.h>
  #include <getopt.h>
  #include <stdio.h>
  
  #include <sys/types.h>
  #include "system.h"
  
  #include "error.h"
  #include "long-options.h"
  #include "quote.h"
  #include "readutmp.h"
  
  /* The official name of this program (e.g., no 'g' prefix).  */
  #define PROGRAM_NAME "users"
  
  #define AUTHORS \
    proper_name ("Joseph Arceneaux"), \
    proper_name ("David MacKenzie")
  
  static int
  userid_compare (const void *v_a, const void *v_b)
  {
    char **a = (char **) v_a;
    char **b = (char **) v_b;
    return strcmp (*a, *b);
  }
  
  static void
  list_entries_users (size_t n, const STRUCT_UTMP *this)
  {
    char **u = xnmalloc (n, sizeof *u);
    size_t i;
    size_t n_entries = 0;
  
    while (n--)
      {
        if (IS_USER_PROCESS (this))
          {
            char *trimmed_name;
  
            trimmed_name = extract_trimmed_name (this);
  
            u[n_entries] = trimmed_name;
            ++n_entries;
          }
        this++;
      }
  
    qsort (u, n_entries, sizeof (u[0]), userid_compare);
  
    for (i = 0; i < n_entries; i++)
      {
        char c = (i < n_entries - 1 ? ' ' : '\n');
        fputs (u[i], stdout);
        putchar (c);
      }
  
    for (i = 0; i < n_entries; i++)
      free (u[i]);
    free (u);
  }
  
  /* Display a list of users on the system, according to utmp file FILENAME.
     Use read_utmp OPTIONS to read FILENAME.  */
  
  static void
  users (const char *filename, int options)
  {
    size_t n_users;
    STRUCT_UTMP *utmp_buf;
  
    if (read_utmp (filename, &n_users, &utmp_buf, options) != 0)
      error (EXIT_FAILURE, errno, "%s", filename);
  
    list_entries_users (n_users, utmp_buf);
  
    free (utmp_buf);
  }
  
  void
  usage (int status)
  {
    if (status != EXIT_SUCCESS)
      emit_try_help ();
    else
      {
        printf (_("Usage: %s [OPTION]... [FILE]\n"), program_name);
        printf (_("\
  Output who is currently logged in according to FILE.\n\
  If FILE is not specified, use %s.  %s as FILE is common.\n\
  \n\
  "),
                UTMP_FILE, WTMP_FILE);
        fputs (HELP_OPTION_DESCRIPTION, stdout);
        fputs (VERSION_OPTION_DESCRIPTION, stdout);
        emit_ancillary_info (PROGRAM_NAME);
      }
    exit (status);
  }
  
  int
  main (int argc, char **argv)
  {
    initialize_main (&argc, &argv);
    set_program_name (argv[0]);
    setlocale (LC_ALL, "");
    bindtextdomain (PACKAGE, LOCALEDIR);
    textdomain (PACKAGE);
  
    atexit (close_stdout);
  
    parse_long_options (argc, argv, PROGRAM_NAME, PACKAGE_NAME, Version,
                        usage, AUTHORS, (char const *) NULL);
    if (getopt_long (argc, argv, "", NULL, NULL) != -1)
      usage (EXIT_FAILURE);
  
    switch (argc - optind)
      {
      case 0:			/* users */
        users (UTMP_FILE, READ_UTMP_CHECK_PIDS);
        break;
  
      case 1:			/* users <utmp file> */
        users (argv[optind], 0);
        break;
  
      default:			/* lose */
        error (0, 0, _("extra operand %s"), quote (argv[optind + 1]));
        usage (EXIT_FAILURE);
      }
  
    return EXIT_SUCCESS;
  }
  