As trs80 notes, Spreadsheet::WriteExcel is still a work in progress, and though there has been a great deal of progress, even the very latest version (0.34 as I type) does not support references to sheets outside the current workbook. As you cannot modify existing workbooks with this module, you can't even add a new empty sheet to your existing Results.xls file, and insert the summary formulas you want in there with references to the relevant existing sheet names.

While you could try Win32::OLE if you are on a Windows platform with Excel installed, you might have an easier time of it if you use Spreadsheet::ParseExcel to read the cells you want from the original spreadsheet, then just create a new workbook with Spreadsheet::WriteExcel, inserting the cells you want to keep, no formulas required.

A final note on your actual code: besides the usual use strict; and use warnings; (or -w as your version allows) admonitions, I'd suggest you use the write($row, $col, $formula) method format, as then you don't need to do any string manipulation to create the Excel-style cell names in your loop.

Update: I had no trouble at all using WinZip to install the latest tar.gz distribution from CPAN.

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I'd like to be able to assign to an luser