Regex expression to match string between two other strings

I think you suppose to use a pattern similar to this

Regex

(?<={% for[^%]*%})((?:.|\n)*)(?={% endfor %})

Explanation

(?<={% for[^%]*%}) : use lookbehind to searching for pattern {% for[^%]*%}

(?={% endfor %}) : use lookahead to searching for text {% endfor %}

((?:.|\n)*) : a message between a for loop which is captured by variable $1

But in case if your language do not support lookaround, you just use this

Regex

({% for[^%]*%})((?:.|\n)*)({% endfor %})

Explanation

({% for[^%]*%}) : capture pattern {% for[^%]*%} to variable $1

({% endfor %}) : capture pattern {% endfor %} to variable $3

((?:.|\n)*) : a message between a for loop which is captured by $2

Just modify my regex according to a restriction in your language then you will done this.

Edit

As I search, I think Javascript do not support lookaround and another thing {, } need to be escape by \. I already tested regex using some online regex tester for Javascript and I get this.

(\{% for[^%]*%\})((?:.|\n)*)(\{% endfor %\})

to get a text that you want, you just use variable $2.

Additional

In case you want to capture message inside nested loop e.g.

Example Message

{% for product in products.pos01 %} 
    ...
    {% for product in products.pos02 %}
         "messages"
    {% endfor %}
    ...
{% endfor %}

To capture "messages" inside this nested loop you just need to modify my previous regex to

(\{% for[^%]*%\}(?:.|\n)*\{% for[^%]*%\})((?:.|\n)*)(\{% endfor %\}(?:.|\n)*\{% endfor %\})

Explanation

(\{% for[^%]*%\}(?:.|\n)*\{% for[^%]*%\}) : means "start of for loop" following by "any characters including newline" and following by "start of for loop"

((?:.|\n)*): our target message

(\{% endfor %\}(?:.|\n)*\{% endfor %\}) : means "end of for loop" following by "any characters including newline" and following by "end of for loop"

Notice that I just rearrange my previous regex to done this little bit more complicated job.

If you're trying to get what is within {% for ... %} and {% endfor %} this might work:

/%}([\W\w]*){%/gm

Explanation:

%} matches the characters %} literally
\W match any non-word character [^a-zA-Z0-9_]
\w match any word character [a-zA-Z0-9_]
{% matches the characters {% literally
g modifier: global. All matches (don't return on first match)
m modifier: multi-line.

Example:

https://regex101.com/r/pM3oX7/1

_{It's unclear if you are wanting to get the text within the %} {% or also include that part.}