$re = '/^(?:BE)?\s*?[0-1]?((\d[. ]*){9})$/m';
$str = 'BE 0123.321.123
BE0123.321.123
BE0123 321 123
1123.321.123
123.321.123
123321123
BE1233221221
BE123322122
BE 0123..... 321 122
BE 01 23 32 11 23
aae233432233 23343';
preg_match_all($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