php regex mach before and after specific word - php

Question

I have a string with data that looks like this:
$string = '
foo=bar
badge_name_foo=foo
bar_badge_name=bar
bar=baz
';
I want to match all *_badge_name and badge_name_* strings.
The regex im using is this:
preg_match_all('~(?:(\w+)_)?badge_name(?:_(\w+))?~', $string, $matches, PREG_SET_ORDER);
The result is:
Array
(
[0] => Array
(
[0] => badge_name_foo
[1] =>
[2] => foo
)
[1] => Array
(
[0] => bar_badge_name
[1] => bar
)
)
The *_badge_name is working fine, but on badge_name_* there is every time a empty value? Now how can i remove that with preg_match_all
Expected result should be:
Array
(
[0] => Array
(
[0] => badge_name_foo
[1] => foo
)
[1] => Array
(
[0] => bar_badge_name
[1] => bar
)
)

Answer 1

It seems you need to use BRANCH RESET feature:
Alternatives inside a branch reset group share the same capturing groups. The syntax is (?|regex) where (?| opens the group and regex is any regular expression. If you don't use any alternation or capturing groups inside the branch reset group, then its special function doesn't come into play. It then acts as a non-capturing group.
Use
(?|(\w+)_badge_name|badge_name_(\w+))
^^^
See the regex demo.
PHP demo:
$re = '/(?|(\w+)_badge_name|badge_name_(\w+))/';
$str = 'foo=bar
badge_name_foo=foo
bar_badge_name=bar
bar=baz';
preg_match_all($re, $str, $matches);
print_r($matches);
Result:
Array
(
[0] => Array
(
[0] => badge_name_foo
[1] => bar_badge_name
)
[1] => Array
(
[0] => foo
[1] => bar
)
)