How to match, but not capture, part of a regex?

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The only way not to capture something is using look-around assertions:

(?<=123-)((apple|banana)(?=-456)|(?=456))

Because even with non-capturing groups (?:…) the whole regular expression captures their matched contents. But this regular expression matches only apple or banana if it’s preceded by 123- and followed by -456, or it matches the empty string if it’s preceded by 123- and followed by 456.

Lookaround Name What it Does
(?=foo) Lookahead Asserts that what immediately FOLLOWS the current position in the string is foo
(?<=foo) Lookbehind Asserts that what immediately PRECEDES the current position in the string is foo
(?!foo) Negative Lookahead Asserts that what immediately FOLLOWS the current position in the string is NOT foo
(?<!foo) Negative Lookbehind Asserts that what immediately PRECEDES the current position in the string is NOT foo

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