$re = '/^]d2(?:
01(?P<g01>.{14})|
10(?P<g10>(?:(?!\[GS]).){1,20})(?:\[GS]|$)|
17(?P<g17>.{6})|
21(?P<g21>(?:(?!\[GS]).){1,20})(?:\[GS]|$)
)+$/mx';
$str = ']d2010704626096200210KT0BT2204[GS]1726090021RNM5F8CTMMBHZSY7]
]d201070462608682672140097289158930[GS]10101656[GS]17261130';
preg_match_all($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