$re = '~\bAM19/0(?!803)[678]\d{2}\b~m';
$str = 'AM19/0601
AM19/0805
AM19/0803
AM19/0601,AM19/0602';
preg_match_all($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