$re = '/^(?:(MORE)|LESS) THAN CAD [\d,]+(?(1)(?: BUT LESS THAN CAD [\d,]+)?)$/m';
$str = 'MORE THAN CAD 10,000
MORE THAN CAD 10,000 BUT LESS THAN CAD 15,000
LESS THAN CAD 10,000
MORE THAN CAD 10,000LESS THAN CAD 15,000
LESS THAN CAD 10,000 BUT LESS THAN CAD 10,000';
preg_match_all($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