Exportar Banco de Dados para SQL Dump em PHP

<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'password';
$dbname = 'test';
$mysqldump=exec('which mysqldump');


$command = "$mysqldump --opt -h $dbhost -u $dbuser -p $dbpass $dbname > $dbname.sql";

exec($command);
?>
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