How to catch nested {% if … %}{% endif %} statments with regex

Question

This is what I got now:

/{% if(.+?) %}(.*?){% endif %}/gusi

It catches multiple if statements etc just fine.

IMG: http://image.xesau.eu/2015

Answer 1

It is almost trivial to change your pattern into a recursive pattern:

{% if(.+?) %}((?>(?R)|.)*?){% endif %}

Working example: https://regex101.com/r/gX8rM0/1

However, that would be a bad idea: the pattern is missing many cases, which are really bugs in your parser. Just a few common examples:

• Comments:

  {% if aaa %}
  123
  
  {% endif %}
  

• String literals:

  {% if aaa %}a = "{% endif %}"{% endif %}
  
  {% if $x == "{% %}" %}...{% endif %}
  

• Escaped characters (you do need escaped characters, right?):

  To start a condition, use \{% if aaa %}
  

• Invalid input:
  It would be nice if the parser can work relatively well on invalid input, and point to the correct position of the error.