First, CGI::Application won't automatically send the file. The script needs to read the file and return the data.

Second, header_props is a function that modifies the header directly. There is no need to assign it to $output at all. The 2/8 you see is result of printing the anonymous hash (header) in scalar context.

Here's a working example:

sub show_excel {
  my $self = shift;
  my $file = "temp.xls";
  my $output = do {
    local $/; open FH, 'temp.xls' or die "$!"; <FH>
  };
  $self->header_props(-type => application/vnd.ms-excel',
                      -attachment => $file);
  return $output;
}
[download]

Finally, it is up to the end user whether to open Excel outside of the browser, embedded in the browser or save the file to disk. A web page can't force it to open in the browser, if that is what you are looking for.

HTH