///********************/
///*  demo_dup2 : ... */
///********************/
# include <stdio.h>
# include <fcntl.h>
# include <unistd.h>

# define ENTREE_STANDARD 0
int main()
{ int descr_group;
  char c;
  descr_group = open ("/etc/passwd", O_RDONLY);
  dup2 (descr_group, ENTREE_STANDARD);/// retour a tester ...
  c = getchar();
  while (c != EOF)
  {
     putchar(c); c = getchar();
  }
  return 0;
}