So Called – Subpatterns

In PHP 5.2.2+ you can name the sub patterns returned from preg_match with a specific syntax.

Named subpatterns now accept the syntax (?<name>) and (?’name’) as well as (?P<name>). Previous versions accepted only (?P<name>)

This is extremely helpful, when dealing with long patterns. As you may know you can simply use the “old school” way and to call the matches by their number based index:

    $haystack = '01 Jan 1970';
    $pattern = '/(\d{1,2})\ (Jan|Feb)\ (19\d\d)/';
 
    preg_match($pattern, $haystack, $matches);
 
    print_r($matches);

Although it may look difficult to maintain, now you can simply name the sub patterns of preg_match and to call them with their associative array keys. This is more clear when writing code and it’s definitely more maintainable.

    $haystack = '01 Jan 1970';
    $pattern = '/(?<day>\d{1,2})\ (?<month>Jan|Feb)\ (?<year>19\d\d)/';
 
    preg_match($pattern, $haystack, $matches);
 
    print_r($matches);
 
    // now there's $matches['day'], $matches['month'] ...