Regex to Grab Content of Recursive Parentheses

✔ Recommended Answer

For the given example, you could use a recursive pattern to match balanced parenthesis right after the @if.

Note that you are matching php code with a regex that may give unexpected side effects.

@if\h*(\(((?:[^()]++|(?1))*)\))\s*(.*?)\s*@endif\b
  • @if\h* Match @if followed by optional spaces
  • ( Capture group 1
    • \( Match (
    • ( Capture group 2
      • (?:[^()]++|(?1))* Repeat matching any char except ( or ) or repeat the first sub pattern
    • ) Close group 2
    • \) Match )
  • ) Close group 1
  • \s*(.*?)\s* Capture group 3, match any character as few as possible between optional whitespace chars
  • @endif\b Match @endif followed by a word boundary

Regex demo | Php demo

$pattern = '/@if\h*(\(((?:[^()]++|(?1))*)\))\s*(.*?)\s*@endif\b/is';$s = '@if(!empty($title)). testand testing   @endif';$subst = "<?php if($2) { ?>$3<?php } ?>";$result = preg_replace($pattern, $subst, $s);echo $result;

Output

<?php if(!empty($title)) { ?>. testand testing<?php } ?>

If you don't want to cross another @if( in between:

@if\h*(\(((?:[^()]++|(?1))*)\))\s*((?:(?!@if\h*\().)*)\s*@endif\b

Regex demo

Method #2

To grab the content of recursive parentheses in PHP using regular expressions, you can use the following regular expression pattern:

scss
/\((?:[^()]+|\((?:[^()]+|\([^()]*\))*\))*\)/

This regular expression pattern matches any text enclosed in parentheses, including nested parentheses.

Here's a breakdown of the pattern:

  • \( : matches an opening parenthesis
  • (?: : starts a non-capturing group
  • [^()]+ : matches one or more characters that are not parentheses
  • | : OR
  • \((?:[^()]+| : matches a nested opening parenthesis, followed by another non-capturing group
  • \([^()]*\) : matches any text enclosed in parentheses that may or may not have nested parentheses
  • )* : ends the nested non-capturing group and specifies that it can be repeated zero or more times
  • )* : ends the non-capturing group and specifies that it can be repeated zero or more times
  • \) `: matches a closing parenthesis

Here's an example of how to use this regular expression pattern in PHP:

php
$text = "This (is (a (nested) example) of) recursive parentheses.";
preg_match_all("/\((?:[^()]+|\((?:[^()]+|\([^()]*\))*\))*\)/", $text, $matches);
print_r($matches[0]);

This will output:

css
Array
(
    [0] => (nested)
    [1] => (a (nested) example)
    [2] => (is (a (nested) example) of)
)

This shows that the regular expression pattern was able to match all the text enclosed in parentheses, including the nested parentheses.

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