How to exclude word from matching that is optional using regex

Question

I want to be able to match the following:

top of pole
top of existing pole
existing top of pole

but not

proposed top of pole

I tried to use ((!=proposed)s)*topsofs(existings)?pole with look back, but it doesn’t quite work, still matching proposed top of pole.

How to exclude certain word when it is optional?

Asked By: ddd

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Answer 1

You can exclude a certain word like this:

(w+s(?<!proposeds))?topsofs(existings)?hole

There are a couple of things going on in this solution:

w+s matches a word and 1 whitespace character,
The negative lookbehind (?<!proposeds) gurantees that, once the regex is at this position after the word and space, looking backwards we do not match "proposed ".
The (...)? makes the (word, space, and no "proposed ") match optional.

For a more detailed walkthrough: https://regex101.com/r/LLs2zA/1

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