#define _GNU_SOURCE
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

extern char **environ;

static char **argv_buffer = NULL;
static size_t argv_size = 0;

int main(int argc, char *argv[]);
void set_proc_title_init(int argc, char *argv[]);
void set_proc_title(const char *format, ...);

int main(int argc, char *argv[])
{
   time_t t;
   struct tm *tmp;
   char s[256];

   set_proc_title_init(argc, argv);
   while(1)
   {
      t = time(NULL);
      tmp = localtime(&t);
      strftime(s, sizeof(s), "%F %T", tmp);
      set_proc_title("You would see my binary's name here, but instead, I'll tell you the time is: %s", s);
      sleep(1);
   }
   exit(0);
   return 0;
}

/* this code borrowed from hal-daemon's util_helper.c */

void set_proc_title_init(int argc, char *argv[])
{
   unsigned int i;
   char **new_environ;
   char *endptr;

   /* This code is really really ugly. We make some memory layout
    * assumptions and reuse the environment array as memory to store
    * our process title in */

   for (i = 0; environ[i] != NULL; i++)
           ;

   endptr = i
          ? environ[i - 1] + strlen(environ[i - 1])
          : argv[argc - 1] + strlen(argv[argc - 1]);

   argv_buffer = argv;
   argv_size = endptr - argv_buffer[0];

   /* Make a copy of environ */

   new_environ = malloc(sizeof(char*) * (i + 1));
   for (i = 0; environ[i] != NULL; i++)
      new_environ[i] = strdup(environ[i]);
   new_environ[i] = NULL;

   environ = new_environ;
}

/* this code borrowed from avahi-daemon's setproctitle.c (LGPL v2) */

void set_proc_title(const char *format, ...)
{
   size_t len;
   va_list ap;

   if (argv_buffer != NULL)
   {
      va_start(ap, format);
      vsnprintf(argv_buffer[0], argv_size, format, ap);
      va_end(ap);
   
      len = strlen(argv_buffer[0]);
   
      memset(argv_buffer[0] + len, 0, argv_size - len);
      argv_buffer[1] = NULL;
   }
}