// Created on savesnippets.com · https://savesnippets.com/S8KKSfba4TzpKZ
<?php
function csvRows(string $path, string $sep = ',', string $enc = '"'): Generator {
    $fh = fopen($path, 'r');
    if ($fh === false) throw new RuntimeException("Cannot open $path");
    try {
        while (($row = fgetcsv($fh, 0, $sep, $enc, '\\')) !== false) {
            yield $row;
        }
    } finally {
        fclose($fh);
    }
}

foreach (csvRows('big-export.csv') as $i => $row) {
    if ($i === 0) continue;        // skip header
    // process $row — uses ~constant memory regardless of file size
}