Easiest and simplest to understand way to me is to use split like this:

  my $a = "index.html";
  my ($filename, $extension) = split /\./, $a;
  print "filename = $filename\n";
  print "extension = $extension\n";
[download]

You can accept a list of values on the left by surrounding them with parenthesis, like 'my ($filename, $extension) = ...'.

HTH.