Non-Capturing Parentheses in PHP Regex

Parentheses () perform two functions - grouping characters and the capturing function. But what to do if we need to group, but not capture? To solve this problem, special non-capturing parentheses (?: ) were invented - they group, but do not capture.

Example

In the following example, the first parentheses are needed for grouping, and the second - for capturing. However, both parentheses save data into the capture group:

php<?php
  $str = 'abab123';
  $reg = '#(ab)+([1-9]+)#';
  preg_match_all($reg, $str, $res);
?>

As a result, our capture groups will contain the following:

php<?php
  var_dump($res[0]); // will output 'abab123'
  var_dump($res[1]); // will output 'ab'
  var_dump($res[2]); // will output '123'
?>

Example

Let's make it so that the first pair of parentheses only groups, but does not capture:

php<?php
  $str = 'abab123';
  $reg = '#(?:ab)+([1-9]+)#';
  preg_match_all($reg, $str, $res);
?>

As a result, the first capture group will contain our number:

php<?php
  var_dump($res[1]); // will output '123'
?>

Practice Tasks

php<?php
  $str = 'aaa$@bbb aaa$@$@bbb aaa$@$@$@bbb';
?>