$re = '/ (?=
({%.if
(?:
(?>
(?:
(?! {%.if | endif.%}) .
)+
)*
| (?1)
)*
endif.%})
)
(?1)/xsm';
$str = '{% if something %}
----------------
{% if something %}
DEEPER
{% endif %}
{% irgendwas %}
{% if something %}
DEEPER
{% if something %}
DEEPEST
{% endif %}
DEEPER
{% endif %}
---- endif ----
{% endif %}
kjafgnkajngkjalkjg
{% if something %}
++++++++++++++++
{% if something %}
DEEPER
{% endif %}
{% irgendwas %}
{% if something %}
DEEPER
{% if something %}
DEEPEST
{% endif %}
DEEPER
{% endif %}
++++ endif ++++
{% endif %}
';
preg_match_all($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