RegEx BackReference to Match Different Values

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Note that \g{N} is equivalent to \1, that is, a backreference that matches the same value, not the pattern, that the corresponding capturing group matched. This syntax is a bit more flexible though, since you can define the capture groups that are relative to the current group by using - before the number (i.e. \g{-2}, (\p{L})(\d)\g{-2} will match a1a).

The PCRE engine allows subroutine calls to recurse subpatterns. To repeat the pattern of Group 1, use (?1), and (?&Val) to recurse the pattern of the named group Val.

Also, you may use character classes to match single characters, and consider using ? quantifier to make parts of the regex optional:

(\(\s*(?P<Val>[a-zA-Z]+[0-9]*|[0-9]+|\'.*\'|\[.*\])\s*(ni|in|[*\/+-]|[=!><]=|[><])\s*((?&Val))\s*\))

See the regex demo

Note that \'.*\' and \[.*\] can match too much, consider replacing with \'[^\']*\' and \[[^][]*\].

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