How can I retrieve the longest matches for substrings enclosed by "{{" and "}}" ?

Question

I am trying to parse a wikitext file received through Wikipedia's API and the problem is that some of its templates (i.e. snippets enclosed in {{ and }}) are not automatically expanded into wikitext, so I have to manually look for them in the article source and replace them eventually. The question is, can I use regex in .NET to get the matches from the text ?

To try to make myself more clear, here is an example to illustrate what I mean:

For the string

{{ abc {{...}} def {{.....}} gh }}

there should be a single match, namely the entire string, so the longest possible match.

On the other hand, for "orphaned" braces such as in this example:

{{ abc {{...}}

the result should be a single match: {{...}}

Could anyone offer me a suggestion ? Thanks in advance.

Answer 1

Don't do it with regex. Go through the string left to right and if you encounter a {{ push its position on a stack, and on a }} pop the position of the previous {{ from the stack and calculate the length. Then you can easily take the maximum of these length.

Answer 2

You can do this with .NET regex using balancing groups definition.

The example given in the documentation shows how it works with nestable < and >. You can easily adapt the delimiters to {{ and }}. You can adapt it further to allow for single { and } within the "text" if you want.

Remember that { and } are regex metacharacters; to match literally, you can escape to \{ and \}.

Answer 3

This regex pattern matches any arbitrary numbers of you mentioned pattern.

\{\{(?:[^{]+\{\{[^}]+\}\})+[^}]+\}\}

For the second request, you'll need a different regex:

\{\{.*?\}\}