$re = '/(?P<symbol>[$¥£€₹])(?P<amount>\d{1,10}(?:[.,]\d{1,10})?)(?:\h+(?P<currency>AUD|USD|GBP|EURO?S?)\b)?\b|(?P<amount>\d{1,10}(?:[.,]\d{1,10})?)\h+(?P<currency>AUD|USD|GBP|EURO?S?)\b/mJ';
$str = '$20,000 AUD
$20,000
20,000 AUD
$
20,000
AUD';
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