$re = '/\d{9}/';
$str = 'blabla n123456789 bla bla 78 texto...
987654321! texto qualquer 12 blaa
123 bla blum 123741852 bobobl
blablum 12345678901 papumpa...';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php