How to capture multiple repeated groups?

Question

I need to capture multiple groups of the same pattern. Suppose, I have the following string:

HELLO,THERE,WORLD

And I've written the following pattern

^(?:([A-Z]+),?)+$

What I want it to do is to capture every single word, so that Group 1 is : "HELLO", Group 2 is "THERE" and Group 3 is "WORLD". What my regex is actually capturing is only the last one, which is "WORLD".

I'm testing my regular expression here and I want to use it with Swift (maybe there's a way in Swift to get intermediate results somehow, so that I can use them?)

UPDATE: I don't want to use split. I just need to now how to capture all the groups that match the pattern, not only the last one.

Answer 1

With one group in the pattern, you can only get one exact result in that group. If your capture group gets repeated by the pattern (you used the + quantifier on the surrounding non-capturing group), only the last value that matches it gets stored.

You have to use your language's regex implementation functions to find all matches of a pattern, then you would have to remove the anchors and the quantifier of the non-capturing group (and you could omit the non-capturing group itself as well).

Alternatively, expand your regex and let the pattern contain one capturing group per group you want to get in the result:

^([A-Z]+),([A-Z]+),([A-Z]+)$

Answer 2

The key distinction is repeating a captured group instead of capturing a repeated group.

As you have already found out, the difference is that repeating a captured group captures only the last iteration. Capturing a repeated group captures all iterations.

In PCRE (PHP):

((?:\w+)+),?

Match 1, Group 1.    0-5      HELLO
Match 2, Group 1.    6-11     THERE
Match 3, Group 1.    12-20    BRUTALLY
Match 4, Group 1.    21-26    CRUEL
Match 5, Group 1.    27-32    WORLD

Since all captures are in Group 1, you only need $1 for substitution.

I used the following general form of this regular expression:

((?:{{RE}})+)

Example at regex101