$re = '/^[.,]?(\d)*([.,](\d+)?)?((?:e[+-]?|[+-]e)*\d+(\.\d+)?)?\.?$/m';
$str = '//Test strings:
//wrong - marked, but should not be becase of \'-\' or \'+\' after mantissa
1.2-
2.3-e
1.2+
1.2+e
//good - marked
1
1.
1.2
123.5
.2
1.2.
.2.
1e3
.e3
1.e3
1.2e3
1.2e+3
1.2e-3
1.2e3.
1.2e3.4
1.2e-399
1.2e+e3
//good - not marked
-123
1.2b+3
+123
-123-e9';
preg_match_all($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