$re = '~\~(.*)\~|\^\((.*)\)~';
$str = 'This is a ~text~ to test the results of substitution of ^(text2). This is how it gets';
$subst = "<sub>\1\2</sub>";
$result = preg_replace($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