my $html;

{
  # $filename and $fh only used here
  # and they won't conflict with anything else

  my $filename = q{some/file.html};
  open my $fh, q{<}, $filename
    or die qq{cant open $filename: $!\n};
  $html = do{local $/;<$fh>};

}

# any previous $filename and $fh remain unharmed