Reg Ex：重复匹配不同值的模式

Question

I'm trying to re-use regex groups for example:

(?<var>[A-Za-z](\d*\w*)*)

Matches most variable names eg abc , abc123 , abc_123 , abc_123_abc and so on.

Is there a way I could re-use this group without typing the whole pattern again?

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For example if I wanted to create a regex to match the below string:

abc_123 AS xyz_89

I would need to create a reg ex like:

^([A-Za-z](\d*\w*)*)( AS )([A-Za-z](\d*\w*)*)$

And to match something like:

abc_123.def_456 AS xyz_89

I would need to use the same pattern 3 times.

It would seem more efficient to be able to refer back to the first group so I'm not repeating regex logic. I've read about back referencing but it seems like they are meant for matching the same value rather than general pattern.

Answer 1

In php , the recursing sub pattern works:

^([A-Za-z](?:\d*\w*)*)( AS )(?1)

The above regex will match:

abc_123 AS xyz_89

Explanation:

1. ([A-Za-z](?:\\d*\\w*)*) Taken from your example and marked as group 1
2. ( AS ) taken from your example, which remains as it is
3. (?1) is a recursing sub pattern of the first group

Demo