Sure, like this:

$worksheet2->write(4,4,'=work1name!B1:B4');
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Here's a sample that works:

#!/usr/bin/perl -w

use strict;

use Spreadsheet::WriteExcel;

# don't need this here, but might in real script to get cell addresses
use Spreadsheet::WriteExcel::Utility;

my $workbook=Spreadsheet::WriteExcel->new("test-counts.xls");
my $files_worksheet=$workbook->addworksheet("Files");

$files_worksheet->write(0,0,"111.cxx");
$files_worksheet->write(0,1,"545");

$files_worksheet->write(1,0,"222.cxx");
$files_worksheet->write(1,1,"333");


my $summ_worksheet=$workbook->addworksheet("Summary");
$summ_worksheet->write(0,0,"Sum:");
$summ_worksheet->write(0,1,"=SUM(Files!B1:B2)");
[download]

Specify the name of your first worksheet, as you'll need it to refer to the cells from the second sheet. I'm not sure what the default sheet name would be if you don't specify it... (Sheet1?)
--
Mike