Redirect a file writer to a variable in PHP using Output Buffers

Published by Arie Oldman on 11 February 2025

Sometimes you have a legacy PHP package which only lets you save data to a file path, while in the modern day we want this data as a blob which we can send to S3 or Cloud Storage. This is how you can use output buffers to capture that data being written to file and redirect it into a variable.

use PhpOffice\PhpSpreadsheet\IOFactory;
// legacy package without write-to-variable support

...

$writer = IOFactory::createWriter($phpExcel, $this->excelVersion);

ob_start();                         // begin capturing output buffer
$objWriter->save('php://output');   // save to the output buffer
$excelData = ob_get_contents();     // read buffer
                                    // now can write this to S3 easily
ob_end_clean();                     // discard the buffer contents