Named capture groups are a feature in PHP regular expressions that improve code readability, which allows capturing groups to be named instead of using only numeric indexes. 1. The naming capture group is defined in syntax similar to (?<name>...), making the code clearer and easier to maintain; 2. PHP's preg_match function supports this function and stores the results in an associative array, such as $matches['year']; 3. There are three equivalent writing methods for naming groups: (?<name>...), (?'name'...), (?P<name>...); 4. When applying, you should avoid duplicate naming, select meaningful names, use them in combination with preg_match_all, and are case-insensitive.

Regular expressions are very powerful when handling strings in PHP, and named capture groups is one of the most practical features. It allows you to assign a name to each capture group instead of just numeric numbers to reference them, making the code written clearer and easier to maintain.

What is a named capture group?

A naming capture group is to name the matching content in brackets. Ordinary capture groups are referenced in such ways as \1 and \2 , while naming capture groups uses syntax similar to (?<name>...)</name> .

For example, the following example:

 /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/

This section is the regular matched to the date format such as 2025-04-05 , and named year, month, and day as year , month and day respectively.

The advantage of this method is that you don’t need to remember which group corresponds to which position, and you can access the corresponding value directly by name.

How to use named capture groups in PHP?

PHP's preg_match function supports naming capture groups and saves the results in an associative array. The key is the name you define in the regular.

Let's give a simple example:

 $subject = "2025-04-05";
$pattern = "/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/";

preg_match($pattern, $subject, $matches);

print_r($matches);

The output result is roughly like this:

 Array
(
    [0] => 2025-04-05
    [year] => 2025
    [month] => 04
    [day] => 05
)

As you can see, in addition to the default index, there are also several keys such as year , month , and day , which are very intuitive.

Several ways to write naming capture groups

PHP supports different styles of naming capture group syntax, and the common ones are as follows:

• (?<name>...) ——The most commonly used one, compatible with Perl style
• (?'name'...) ——Use single quotes to wrap names, which is also common
• (?P<name>...) —— Python compatible writing, which may be more common in older versions of PHP

These three writing methods are the same in function, and you can choose which one to use according to your personal preferences or project specifications.

For example:

 // All three ways of writing can be $pattern1 = "/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/";
$pattern2 = "/(?&#39;year&#39;\d{4})-(?&#39;month&#39;\d{2})-(?&#39;day&#39;\d{2})/";
$pattern3 = "/(?P<year>\d{4})-(?P<month>\d{2})-(?P<day>\d{2})/";

Practical application suggestions

• Avoid duplicate naming : Do not give multiple capture groups the same name in the same rule, otherwise the ones that appear later will overwrite the previous one.
• The name should be meaningful : for example, when matching the URL path, you can use controller , action , id , etc. as the name to facilitate subsequent processing.
• Use in combination with preg_match_all : If you want to extract multiple content that meets the criteria, it can easily obtain structured data with preg_match_all .
• Pay attention to case sensitivity : Are named groups case sensitive? The answer is - no distinction. (?<name>...)</name> and (?<name>...)</name> will be considered the same.

Basically that's it. Although naming capture groups is not necessary, once used, you will find that it can really make the code clearer, especially when dealing with complex strings. As long as you spend a little more time writing the rules, it will be much easier to read and maintain later.

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