csv_write.php

<?php

$list[] = array ("name","gender","age"); 
$values = [
    array("Hello","M","21"),
    array("Syed","M","30"),
    array("Rishat","F","25")
];

for($i = 0; $i < 20000; $i++) {
    $list[] = $values[rand(0,2)];
}


$filename = __DIR__ . "/files/" . "myCSV.csv";

if(file_exists($filename)) {

    unset($list[0]);
    $handle = fopen($filename, "a");

    foreach ($list as $fields) {
       
        fputcsv($handle, $fields);
    }

    fclose($handle);

} else {

    $fp = fopen($filename, 'w');

    foreach ($list as $fields) {
        fputcsv($fp, $fields);
    }

    fclose($fp);
}

echo "done";