Regex pattern to match nested contents of fixed depth

Question

As far as this answer shows (Can regular expressions be used to match nested patterns?) we cannot create a regex that can be used to match a infinitely nested pattern. But can we create a regex pattern that matches up to N nested occurences of that pattern?

For example how could we create a regex that matches comments like this up to 3 layers deep?

   <*
      Comment of depth 1 containing another comment
      <* 
         That is a comment of depth 2 containing another comment
         <*
            Nanananananana BATMAN!!!
         *>
      *> 
    *>

vks · Answer 1 · 2015-04-17T18:27:42.557

0

<\*[\s\S]*?<\*[\s\S]*?<\*[\s\S]*?\*>[\s\S]*?\*>[\s\S]*?\*>

A simple way .See demo.

https://regex101.com/r/sJ9gM7/129

You can use recursive regex here.

<\*(?:(?R)|(?:(?!<\*|\*>)[\s\S])+)*\*>

See demo.

https://regex101.com/r/sJ9gM7/131

edited Apr 17 '15 at 18:27

answered Apr 17 '15 at 17:57

vks

67,027
10
91
124

Your comment works only with nested comments of fixed depth 3. Is it possible to make it to match UP to depth 3? – Fr0stBit Apr 17 '15 at 18:07
@TheArtist which language? – vks Apr 17 '15 at 18:10
Just a personal project :) – Fr0stBit Apr 17 '15 at 18:12
@TheArtist yeah still i mean what would you be using ? php?java? – vks Apr 17 '15 at 18:12
I am using C++, but the thing is that i will integrate the regex in a BNF definition that is fed up to an external library i am using. The library is this: https://github.com/orangeduck/mpc – Fr0stBit Apr 17 '15 at 18:17
@vks The library he is using does not support those regex features. Take a look at this issue: https://github.com/orangeduck/mpc/issues/28 – TheCrafter Apr 17 '15 at 19:54

score 0 · Accepted Answer · answered Apr 19 '15 at 06:29

You said in a comment that you will integrate the regex ain a BNF definition that will be fed up to the library "mpc".

Try to define the multiline comment like this:

mlcomment    : "<*" (<mlcomment> | /\*[^>]|[^*]/)* "*>" ;

I tried it with mpc and it works.

You can have comments not matter if they are nested. For example:

<* A multiline comment here
<* Another one here *> *>

The downside of this is that you cannot have multiple asterisks on the closing tag. This:

<* A multiline comment
second line **>

is not going to work. But I think it is as close as it gets with the limitations of mpc.

Regex pattern to match nested contents of fixed depth

2 Answers2