output = popen ("/bin/cat >tstpopen.tmp", "w");
output = popen ("/bin/cat >/tmp/tstpopen.tmp", "w");
DEFUN_VOID(main){  FILE *output, *input;  int wstatus, rstatus;  output = popen ("/bin/cat >tstpopen.tmp", "w");  if (output == NULL)    {      perror ("popen");      puts ("Test FAILED!");      exit (1);    }  write_data (output);  wstatus = pclose (output);  printf ("writing pclose returned %d\n", wstatus);  input = popen ("/bin/cat tstpopen.tmp", "r");  if (input == NULL)    {      perror ("tstpopen.tmp");      puts ("Test FAILED!");      exit (1);    }  read_data (input);  rstatus = pclose (input);  printf ("reading pclose returned %d\n", rstatus);  puts (wstatus | rstatus  ? "Test FAILED!" : "Test succeeded.");  exit (wstatus | rstatus);}