/*
 *----------------------------------------------------------------------
 *           "THE BEER-WARE LICENSE" (Revision 42):
 * <jeang3nie@HitchHiker-Linux.org> wrote this file. As long as you
 * retain this notice you can do whatever you want with this stuff. If
 * we meet some day, and you think this stuff is worth it, you can buy
 * me a beer in return.
 * ---------------------------------------------------------------------
 *            ______   _______  _          _________
 *           (  __  \ (  ___  )( (    /|( )\__   __/
 *           | (  \  )| (   ) ||  \  ( ||/    ) (
 *           | |   ) || |   | ||   \ | |      | |
 *           | |   | || |   | || (\ \) |      | |
 *           | |   ) || |   | || | \   |      | |
 *           | (__/  )| (___) || )  \  |      | |
 *           (______/ (_______)|/    )_)      )_(
 *
 *         _______  _______  _       _________ _______
 *        (  ____ )(  ___  )( \    /|\__   __/(  ____ \
 *        | (    )|| (   ) ||  \  ( |   ) (   | (    |/
 *        | (____)|| (___) ||   \ | |   | |   | |
 *        |  _____)|  ___  || (\ \) |   | |   | |
 *        | (      | (   ) || | \   |   | |   | |
 *        | )      | )   ( || )  \  |___) (___| (____|\
 *        |/       |/     \||/    \_)\_______/(_______/
 *
 */

#define _DEFAULT_SOURCE

#include <sys/param.h> // HOST_NAME_MAX

#include <libgen.h>    // basename
#include <stdio.h>     // printf, fprintf
#include <stdlib.h>    // exit
#include <string.h>    // strlen
#include <unistd.h>    // gethostname, sethostname, getopt

static const char *__progname;

static void usage() {
  fprintf(stderr,
      "Usage: %s [-s] [name-of-host]\n", __progname);
      exit(EXIT_FAILURE);
}

int main(int argc, char *argv[]) {
  __progname = basename(argv[0]);
  if (argc > 2)
    usage();
  int c, sflag = 0;
  while ((c = getopt(argc, argv, "s")) != -1)
    switch (c) {
      case 's':
        sflag = 1;
        break;
      case '?':
      default:
        usage();
    }
  if (argv[optind] != NULL) {
    char * hostname[HOST_NAME_MAX];
    *hostname = argv[optind];
    if (sethostname(*hostname, strlen(*hostname)) != 0) {
      perror("sethostname");
      exit(EXIT_FAILURE);
    }
  } else {
    char hostname[HOST_NAME_MAX + 1];
    if (gethostname(hostname, sizeof(hostname)) != 0) {
      perror("gethostname");
      exit(EXIT_FAILURE);
    }
    if (!sflag) {
      puts(hostname);
    } else {
      char * val = strtok(hostname, ".");
      puts(val);
    }
  }
  return 0;
}