$output = [
               [ [0],[0],[0] ],
               [ [1,1,1],[1,1,1],[1,1,1] ],
               [ [2,2,2],[2,2,2],[2,2,2] ],
               [ [3,3,3],[3,3,3],[3,3,3] ],
               [ [4,4,4],[4,4,4],[4,4,4] ],
               [ [5,5,5],[5,5,5],[5,5,5] ],
               [ [6,6,6],[6,6,6],[6,6,6] ],
               [ [7,7,7],[7,7,7],[7,7,7] ],
               [ [8,8,8],[8,8,8],[8,8,8] ],
               [ [9,9,9],[9,9,9],[9,9,9] ],
              ];

#...other code that sets up the Excel sheet...

my $Book = $Excel->Workbooks->Open("$excelfile");

for $i (1..9) {
  my $Sheet = $Book->Worksheets("$i");
  $Sheet->Range("A1:C3")->{'Value'} = $$output[$i];
}

##</code><code>##

open (FILEIN,"$filein") or die "Open $filein failed: $!";
while (<FILEIN>) {
    @data = split;
    push @$output, [@data];
}    
close FILEIN;

#...other code that sets up the Excel sheet...

my $Book = $Excel->Workbooks->Open("$excelfile");
my $Sheet = $Book->Worksheets("$sheetname");

# ...other code that determines
#       $begcol,$begrow,$endcol,endrow

$Sheet->Range("$begcol$begrow:$endcol$endrow")->{'Value'} = $output;


##</code><code>##

push @$output, [@data];

##</code><code>##

push $$day_output[$data[1]], [@data];