If you want to avoid the "Number stored as text" warnings in Excel then you will have to write the data as numbers and format it to have a padded leading zero. Item 3 of the example below demonstrates this.

    #!/usr/bin/perl -w


    use strict;
    use Spreadsheet::WriteExcel;

    my $workbook  = Spreadsheet::WriteExcel->new('test.xls');
    my $worksheet = $workbook->addworksheet();


    # A padded number format
    my $format = $workbook->add_format(num_format => '0000');

    # 1. Implicitly write a number, the leading zero is removed: 123
    $worksheet->write('B2', '0123');

    # 2. Write explicitly as a string: 0123
    $worksheet->write_string('B3', '0123');

    # 3. Write a zero padded number using a format: 0123
    $worksheet->write('B4', '0123', $format);

    __END__
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--
John.