$re = '/(?s)(BEGIN.*?BOOL\:TRUE.*?END)/';
$str = 'BEGIN
DESCRIPTION: 1234
BOOL:TRUE
END
BEGIN
DESCRIPTION: 4568
BOOL:TRUE
END
BEGIN
DESCRIPTION: 715310
BOOL:FALSE
END
BEGIN
DESCRIPTION: 12489453
BOOL:TRUE
END
BEGIN
DESCRIPTION: 41543
BOOL:FALSE
END';
preg_match_all($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