$re = '/(?x)
^(?!.*[\s]) # this excludes whitespaces
(?=.*\d) # this matches at least one digit
(?=.*[a-z]{0,}) # this matches 0 or more lowercase letters
(?=.*[A-Z]) # this matches at least one uppercase character
.{8,}$ # ensuring the minimum length is 8 symbols
# ^(?!.*[\s])(?=.*\d)(?=.*[a-z]{0,})(?=.*[A-Z]).{8,}$ the whole RegEx/m';
$str = '';
preg_match_all($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