How to negate a substring only in a certain section of the string with regex?

I'm trying to achieve the following thing: I want to negate the appearance of the substring '::' but only in a certain section of the string. For example:

a<anyStringWithout'::'>b<anyStringAlsoWith'::'>

I tried to do that with negative lookahead like this:

a(?!.*::).*b

But occurrences of '::' after 'b' also make the string to unmatch, for example: 'acb::'

Is there a way to achieve what I want with regex?

Thanks in advance!

Solution

You can use

a(?:(?!a|b|::).)*b

This matches any string that starts with a pattern, then matches any char that does not start the a, b and :: patterns, zero or more times, up to the b pattern.

Details

a - an a pattern
(?: - start of a non-capturing group:
- (?!a|b|::) - a negative lookahead that fails the match if there is a, b or :: immediately to the right of the current location
- . - any char but a line break char
)* - zero or more times
b - a b pattern.