I use Spreadsheet::WriteExcel opened to an in-memory filehandle:

open my $fh, '>', \my $buffer;
my $workbook  = Spreadsheet::WriteExcel->new($fh);
...
close $fh;
print $buffer;
[download]

I tried it, but I seem to do something wrong.

I simply took the example from the documentation but simply get a 0 byte file. I will continue investigating, but maybe someone of you has some information what might be wrong?

This is what I have in my Dancer route:

content_type 'application/vnd.ms-excel';
my $buffer;
open my $fh, '>', \$buffer;
my $workbook  = Spreadsheet::WriteExcel->new($fh);
my $worksheet = $workbook->add_worksheet();
#  Add and define a format
my $format = $workbook->add_format(); # Add a format
$format->set_bold();
$format->set_color('red');
$format->set_align('center');
        
# Write a formatted and unformatted string, row and column notation.
my $col = 0;
my $row = 0;
$worksheet->write($row, $col, 'Hi Excel!', $format);
$worksheet->write(1,    $col, 'Hi Excel!');
        
# Write a number and a formula using A1 notation
$worksheet->write('A3', 1.2345);
$worksheet->write('A4', '=SIN(PI()/4)');
close $fh;
return $buffer;
[download]

Found the mistake
I forgot $workbook->close();.

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+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

One option would be to create a CSV file, which Excel can read.

If the HTML output is a table, I've also seen one approach of saving the page via the browser and give it an .xls file extension. Excel seems to be able to open and read this. Not exactly a "pretty" solution, but it seems to work. (Not advocating this route. Just tossing out ideas.)

If the web server happens to be on a Windows system that has Excel installed, you could also use Win32::OLE to control Excel to create the Excel file for download. Otherwise, my guess is that Corion's suggestion maybe the best route to go.

++ for the idea.

The disadvantages of CVS are, as far as I can see:

1. the user needs to specify the column formats when importing/opening the file
2. columns are most times misinterpreted if you choose "standard"
3. numbers get mixed up

That's why I always used MMM::Sylk. I'm trying now out Excel::Writer::XLSX as it is the successor of the module Corion recommended.

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s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e