Regex - Capture first 2 characters of a capturing group-CodePudding

I want to match with one of strings: ab10, cd14, ef23, mn99
Regex: (ab10|cd14|ef23|mn99)
How can I capture words: ab, cd, ef, mn (first 2 characters of group $1)

CodePudding user response：

You can add a (?=(..)) or (?=(.{2})) lookahead containing another capturing group at the start:

(?=(..))(ab10|cd14|ef23|mn99)
(?=(.{2}))(ab10|cd14|ef23|mn99)

See the regex demo.

The two chars will land in Group 1 and the full found match in Group 2.

Another way to get it is via a branch reset group:

(?|(ab)10|(cd)14|(ef)23|(mn)99)

See this regex demo. The two char combinations will be in Group 1.