正则表达式捕获组流入第二个匹配集

Question

I am trying to match multiple inputs in the same regex to capture the number following.
If the input doesnt match the first group then I have issues because all previous capture groups are still captured despite it doesnt match they group. I believe I need to use a lookaround assertion, but I am not familiar with those.

Sample input:

wordA 123456
wordA: 123456
wordA : 123456
wordA R123465
wordA: R123456
wordA : R123456
wordB R123465

WordA has both optional : and R. So far I have this: /(?:wordA :?R?(\d+)|wordB R(\d+))/i.
Using the last sample input provides this result:

array
  0 => string 'wordB R123456' (length=13)
  1 => string '' (length=0)
  2 => string '123456' (length=6)

Wanted result is:

array
  0 => string 'wordB R123465' (length=13)
  1 => string '123456' (length=6)

Any ideas how to fix ?

Answer 1

The problem is your alternation

/(?:wordA :?R?(\d+)|wordB R(\d+))/i
              ^^^^^        ^^^^^
             Group 1       Group 2

So if your regex matches the second alternative, the result will be in group 2 (array[2]) and the first group will be empty.

Change it to this

(?:wordA :?R?|wordB R)(\d+)

See it here on Regexr

Then your number will always be in the first group (because there is only one)