$re = '/(?:(?:edit (\S+))|(KeyWord_1|KeyWord_2|KeyWord_3)|\b([0-9A-Z])\b)(?=(?:(?!edit[^;]+;mode )[\s\S])*?exit)/mi';
$str = 'edit GoodMatch1 ;mode
Something Random
KeyWord_2 A B and C and also D E
Something Random
Something Random
KeyWord_3 1 A and 2 B
Something Random
KeyWord_1 1 2 and 3 and also 4 5
Something Random
exit';
preg_match_all($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