Spreadsheets, driven by code.

<?php

require 'vendor/autoload.php';

use \PhpOffice\PhpSpreadsheet\IOFactory;
use \PhpOffice\PhpSpreadsheet\Writer\Csv;

// Read the workbook. Only the values matter for a CSV.
$reader = IOFactory::createReaderForFile('products.xlsx');
$reader->setReadDataOnly(true);
$spreadsheet = $reader->load('products.xlsx');

// Describe the CSV to write.
$writer = new Csv($spreadsheet);
$writer->setDelimiter(',');
$writer->setEnclosure('"');
$writer->setLineEnding("\r\n");

// Without the BOM, Excel reads UTF-8 as its own legacy encoding.
$writer->setUseBOM(true);

// A CSV holds one sheet. Pick which one by index.
$writer->setSheetIndex(0);

$writer->save('products.csv');

$rows = $spreadsheet->getActiveSheet()->getHighestRow();
echo "Done. Converted products.xlsx ($rows rows) to products.csv\n";