#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main (const int argc, char *argv[], char *envp[])
{
  if (argc != 2)
    {
      fprintf (stderr, "Usage: %s -1\n", argv[0]);
      exit (1);
    }

  const int flag = atoi (argv[1]);

  if (flag == -1)
    {
      const int fd = open ("/etc/passwd", O_RDONLY);

      if (fd == -1)
	{
	  perror ("/etc/passwd");
	  exit (1);
	}

      if (fcntl (fd, F_SETFD, FD_CLOEXEC) == -1)
	{
	  perror ("fcntl");
	  exit (1);
	}

      pid_t pid = fork ();

      switch (pid)
	{
	case -1:
	  perror ("fork");
	  exit (1);

	case 0:                     // child
	  {
	    char buf[BUFSIZ];
	    sprintf (buf, "%d", fd);
	    argv[1] = buf;
	    execve (argv[0], argv, envp);
	  }
	  break;

	default:                    // parent
	  {
	    int status;
	    if (wait (&status) == -1)
	      {
		perror ("wait ()");
		exit (1);
	      }
	  }
	  break;
	}
    }
  else
    {
      char buf[BUFSIZ];
      ssize_t len = read (flag, buf, sizeof (buf));
      if (len == -1)
	{
	  perror ("/etc/passwd");
	  exit (1);
	}
      write (1, buf, len);
    }

  return 0;
}