This is my best current guess at what you are trying to do:

use warnings;
use strict;
use Spreadsheet::WriteExcel;

my $workbook = Spreadsheet::WriteExcel->new("data.xls");
my $worksheet = $workbook->add_worksheet();

$worksheet->write ("A1", 'Device');
$worksheet->write ("B1", '/var');
$worksheet->write ("C1", '/');
$worksheet->write ("D1", 'interleaved');

my $row = 2;

#Assume data is actually on one line
while (<DATA>)
  {
  my ($p1, $p2, $p3, $device) = /(?:\. ){3}(\d+)%\s\/var\s(\d+).*?(\d+
+)%\sInterleaved (\w+)/;
  $worksheet->write("A$row", $device);
  $worksheet->write("B$row", $p1);
  $worksheet->write("C$row", $p2);
  $worksheet->write("D$row", $p3);
  ++$row;
  print "$device $p1, $p2, $p3\n";
  }

$workbook->close ();

__DATA__
2.3.5.1 . . . 56% /var 38% / 31% Interleaved device1 Tue Sep  9 11:26:
+44 ist 2005
2.3.5.1 . . . 56% /var 38% / 31% Interleaved device2 Tue Sep  5 10:26:
+44 GMT 2005
[download]

Prints:

device1 56, 38, 31
device2 56, 38, 31
[download]

It pulls report lines from a file (in the sample code from the __DATA__ section), checks that the data pertains to device1, extracts the first two % values and writes those to columns A and B respectively in an Excel spreadsheet file.