sub is_writable_fh
{
  my($fh)=@_;
  local $\='';
  return print $fh '';
}

open(F1,"< $0")
  or die "Couldn't open '$0' for read: $!\n";
print "F1 is".(is_writable_fh(\*F1)?"":"n't")." writable.\n";

open(F2,">> $0")
  or die "Couldn't open '$0' for append: $!\n";
print "F2 is".(is_writable_fh(\*F2)?"":"n't")." writable.\n";