$re = '/(\s|^)(?s)\d{1,3}+\/+\s+.*?(?=\d+\/+\s+|$)/m';
$str = '1/ This is a string and it
has some text on a new line
2/ And then there\'s another string that has text only on one line
532/ Another string that has some year on a new line
2020/xyz followed by some letters
721/ And this is the last line ';
preg_match_all($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