get inner patterns recursively using regex c#

Question

i know there are several questions about regex recursion in .net. I can write somewhat complex regex expressions but this recursion is beyond me, i am just not able to write it.

This are the questions closest to what i want.

first question, second question.

but it matches the entire string, i want the matches in a collection preferably the innermost match first or in some order. Also it matches on one opening character and one closing character. Mine is 2 chars for opening and closing, [! and !]

my input string will be something like this.

[!a='test' b='[!a='innertest' b='innervalue'!]'!]

I need to find the innertest section, [!a='innertest' b='innervalue'!], first and then evaluate it through one of my expression trees. then evaluate the parent one containing it.

Can anyone help with this?

Answer 1

Here's a pattern that might satisfy your needs:

^\[!((?<n>\w+='\[!)|(?<inner-n>!]')|\w+='(?!\[!)[^']*'| )*!](?!(n))$

It will give the innermost item for each item in order. To explain what I mean, given the code:

[!a='test' c='[!x='blah'!]' b='[!a='[!y='innermost'!]' b='innervalue'!]' !]

It will give the following matches (in the capture collection for the group "inner"):

x='blag'
y='innermost'
a='[!y='innermost'!]' b='innervalue'

So, for each x=y item in the [! .. !], it will give the matches in order from innermost outwards.

If you also want the overall expression to be captured you can modify it like this:

^(?<n>\[!)((?<n>\w+='\[!)|(?<inner-n>!]')|\w+='(?!\[!)[^']*'| )*(?<inner-n>!])(?!(n))$

Giving:

x='blag'
y='innermost'
a='[!y='innermost'!]' b='innervalue'
a='test' c='[!x='blag'!]' b='[!a='[!y='innermost'!]' b='innervalue'!]' 

---

And to explain the regex:

^       # start of string
\[!     # start of overall [! .. !]
(       # either ...
    (?<n>\w+='\[!)|     # a complex x='[! .. !]' containing a nested [! .. !] - push this onto the stack 'n'
    (?<inner-n>!]')|    # end of a nested [! .. !] - pop stack 'n', and capture the contents into 'inner'
    \w+='(?!\[!)[^']*'| # a simple x='asdf' with no nested [! .. !]
     )                  # or a space
*       # as many times as you want
!]      # the end of the overall [! .. !]
(?!(n)) # assert that the 'n' stack is empty, no mismatched [! .. !]
$       # end of string