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PORegex to capture an optional group in the middle of a block of input
 

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    <p>I'm stuck on a RegEx problem that's seemingly very simple and yet I can't get it working.</p> <p>Suppose I have input like this:</p> <pre><code>Some text %interestingbit% lots of random text lots and lots more %anotherinterestingbit% Some text %interestingbit% lots of random text OPTIONAL_THING lots and lots more %anotherinterestingbit% Some text %interestingbit% lots of random text lots and lots more %anotherinterestingbit% </code></pre> <p>There are many repeating blocks in the input and in each block I want to capture some things that are always there (%interestingbit% and %anotherinterestingbit%), but there is also a bit of text that may or may not occur in-between them (OPTIONAL_THING) and I want to capture it if it's there.</p> <p>A RegEx like this matches only blocks with OPTIONAL_THING in it (and the named capture works):</p> <pre><code>%interestingbit%.+?((?&lt;OptionalCapture&gt;OPTIONAL_THING)).+?%anotherinterestingbit% </code></pre> <p>So it seems like it's just a matter of making the whole group optional, right? That's what I tried:</p> <pre><code>%interestingbit%.+?((?&lt;OptionalCapture&gt;OPTIONAL_THING))?.+?%anotherinterestingbit% </code></pre> <p>But I find that although this matches all 3 blocks the named capture (OptionalCapture) is empty in all of them! How do I get this to work?</p> <p>Note that there can be a lot of text within each block, including newlines, which is why I put in ".+?" rather than something more specific. I'm using .NET regular expressions, testing with The Regulator.</p>
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