$re = '/{%\ (if)[\s\S]*?{%\ end\1\ %}|
{%.+?%}|
{{.+?}}/x';
$str = '<div class="post-preview">
<div class="post-title">
<div class="post-name">
<a href="{{ post.url }}">{{ post.title }}</a>
</div>
<div class="post-date">
{% include time.html %}
</div>
</div>
<div class="post-snippet">
{% if post.content contains \'<!--break-->\' %}
{{ post.content | split:\'<!--break-->\' | first }}
<div class="post-readmore">
<a href="{{ post.url }}">read more-></a>
</div>
{% endif %}
</div>
{% include post-meta.html %}
</div>';
$subst = "";
$result = preg_replace($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