$re = '/((?:\d{1,2}[\/-]){2}(?:\d{4}|\d{2}))/';
$str = 'ASTA n° 30 | 13/12/2015 ore 10.00 | Arte Moderna & Contemporanea
ASTA n° 30 | 1/12/2015 ore 10.00 | Arte Moderna & Contemporanea
ASTA n° 30 | 13/1/2015 ore 10.00 | Arte Moderna & Contemporanea
ASTA n° 30 | 13-12-2015 ore 10.00 | Arte Moderna & Contemporanea
ASTA n° 30 | 13/12-2015 ore 10.00 | Arte Moderna & Contemporanea
ASTA n° 30 | 13/12/15 ore 10.00 | Arte Moderna & Contemporanea';
preg_match_all($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