$re = '/\<\<(.*)\=\=(\1)\?\?(.*)\%\%(.*)\>\>|\<\<(.*)\=\=(.*)\?\?(.*)\%\%(.*)\>\>/mU';
$str = 'fdlkg jfdklgj fdkl <<xxx==xxx??aaa%%bbb>> gjfkl jgfdlkgj <<xxx==yy??ddd%%eee>> fdsklgj fdsklgj fdklgjf';
$subst = "$3$8";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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