$re = '/^[1-9]\d*(.\d+)?$/m';
$str = '1.2345
123.45
123.
.12345
0.1234
4.1234
4x1234
1-23455';
preg_match_all($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