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| <?php | |
| $regex1 = '/(\d+) \1/'; // Backreference | |
| $regex2 = '/(\d+) (?1)/'; // Subroutine | |
| 100 100 // ✅ only backreference | |
| 100 200 // ✅ both! | |
| // https://github.com/Hamz-a/php-regex-best-practices/blob/master/07%20Writing%20modular%20regexes.md | |
| // named subroutines | |
| $regex = '/(?<number>\d+),(?&number)/'; // Named subroutine | |
| // advanced | |
| $regex = <<<'regex' | |
| ~ | |
| (?(DEFINE) | |
| (?<id>\d+) | |
| (?<username>user(?&id)) | |
| (?<protocol>https?|ftp) | |
| (?<domain>example[.]com) | |
| (?<url>(?&protocol)://(?&domain)/users/(?&id)/(?&username)/?) | |
| ) | |
| ^(?&url)$ # Anchor our match | |
| ~x | |
| regex; |
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