$re = '/(?|([a-zA-Z0-9]+)\(([a-zA-Z\s]+)\)|\(([a-zA-Z\s]+)\)([a-zA-Z0-9]+))/';
$str = '(Weather) is good. // not need to mark this beacuase this word konown word
Weath(er) is good. // mark
Weath(er is good). // mark
Weather (is) (good).
My name is Rah(eel) // mark
Best pro(duct) // mark
(Weather is good) // not need to mark this beacuase this word konown word
we(ather)
(weath)er is good. // i want to mark this word
(weath)er // i want to mark this word
weather(is fine)
';
preg_match_all($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