Matching an optional substring in a regex

by 
(\d+)\s+(\(.*?\))?\s?Z

Note the escaped parentheses, and the ? (zero or once) quantifiers. Any of the groups you don’t want to capture can be (?: non-capture groups).

I agree about the spaces. \s is a better option there. I also changed the quantifier to insure there are digits at the beginning. As far as newlines, that would depend on context: if the file is parsed line by line it won’t be a problem. Another option is to anchor the start and end of the line (add a ^ at the front and a $ at the end).

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