Get repeated matches with preg_match_all()

Question

I'm trying to get all substrings matched with a multiplier:

$list = '1,2,3,4';
preg_match_all('|\d+(,\d+)*|', $list, $matches);
print_r($matches);

This example returns, as expected, the last match in [1]:

Array
(
    [0] => Array
        (
            [0] => 1,2,3,4
        )

    [1] => Array
        (
            [0] => ,4
        )

)

However, I would like to get all strings matched by (,\d+), to get something like:

Array
(
    [0] => ,2
    [1] => ,3
    [2] => ,4
)

Is there a way to do this with a single function such as preg_match_all()?

Answer 1

It's true that PHP (or better to say PCRE) doesn't store values of repeated capturing groups for later access (see PCRE docs):

If a capturing subpattern is matched repeatedly, it is the last portion of the string that it matched that is returned.

But in most cases the known token \G does the job. \G 1) matches the beginning of input string (as \A or ^ when m modifier is not set) or 2) starts match from where the previous match ends. Saying that, you have to use it like the following:

preg_match_all('/^\d+|\G(?!^)(,?\d+)\K/', $list, $matches);

See live demo here

or if capturing group doesn't matter:

preg_match_all('/\G,?\d+/', $list, $matches);

by which $matches will hold this (see live demo):

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => ,2
            [2] => ,3
            [3] => ,4
        )

)

Note: the benefit of using \G over the other answers (like explode() or lookbehind solution or just preg_match_all('/,?\d+/', ...)) is that you are able to validate the input string to be only in the desired format ^\d+(,\d+)*$ at the same time while exporting the matches:

preg_match_all('/(?:^(?=\d+(?:,\d+)*$)|\G(?!^),)\d+/', $list, $matches);