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

Question

I have a list of strings. Some of them are of the form 123-...456. The variable portion \"...\" may be:

• the string \"apple\" followed by a hyphen,

Answer 1

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   | Asserts that what immediately FOLLOWS the |
|            |   Lookahead  |  current position in the string is NOT foo|
-------------------------------------------------------------------------
|(?