Regular expression to match and remove unclosed parenthesis

Question

I have a couple of strings I'd like to remove unclosed brackets such as ( or [

"A Pro Webcam ((Good text) [[Good Text] more texts"

"Text (Example (Good text) [Good Text] more texts"

I have tried using this with php with no luck

\((?:[^)(]*(?R)?)*+\)

How can you possibly know which one is unclosed? I.e., should `(Example (Good text)` be `(Example Good text)` or `Example (Good text)`? — Alex Howansky, Nov 03 '22 at 18:51
An idea to [skip](https://stackoverflow.com/questions/24534782/how-do-skip-or-f-work-on-regex) the good things and match what's left. See [this demo](https://regex101.com/r/mffQsD/1). — bobble bubble, Nov 03 '22 at 18:56
@Claudio Not exactly considering the accepted answer returns a boolean value there. — nice_dev, Nov 03 '22 at 19:01
Thank you very much guys, I'll be going with the non-regex approach for the sake of others that might want to maintain the codebase in my absence or do not understand regex. Much love . — electrode, Nov 08 '22 at 11:48

nice_dev · Answer 1 · 2022-11-03T19:36:47.297

Match pairs of ( and ) and [ and ] using a stack. If there is a mismatch in such a pair of characters OR if the characters are not available(meaning hanging closed parentheses), collect all such guys in array to be skipped later when creating a clean string.

<?php

function filterUnmatchedParentheses($string){
  $opened = [];
  $unOpened = [];
  $skipIdxs = [];
  $length = strlen($string);
  
  for($i = 0; $i < $length; ++$i){
    if($string[ $i ] === '(' || $string[ $i ] === '['){
      $opened[] = $i;
    }else if($string[ $i ] === ')' || $string[ $i ] === ']'){
      $matchFound = false;
      while(count($opened) > 0){
        $idx = array_pop($opened);
        $char = $string[ $idx ];
        if($char == '(' && $string[ $i ] === ')' || $char == '[' && $string[ $i ] === ']'){
          $matchFound = true;
          break;
        }
        $skipIdxs[] = $idx;
      }
      
      if(!$matchFound){
        $unOpened[] = $i;
      }
    }
  }
  
  $skipIdxs = array_flip(array_merge($skipIdxs, $opened, $unOpened));
  
  $res = "";
  
  for($i = 0; $i < $length; ++$i){
    if(isset($skipIdxs[ $i ])) continue;
    $res .= $string[ $i ];
  }
  
  return $res;
}

Online Demo

score 1 · Answer 2 · answered Nov 03 '22 at 19:18

1

You can use

(?:(\((?:[^()]++|(?1))*\))|(\[(?:[^][]++|(?2))*]))(*SKIP)(*F)|[][()]

See the regex demo. Replace with an empty string.

Details:

(?:(\((?:[^()]++|(?1))*\))|(\[(?:[^][]++|(?2))*]))(*SKIP)(*F) - a string between paired ( and ) or between [ and ]
| - or
[][()] - a [, ], ( or ).

answered Nov 03 '22 at 19:18

Wiktor Stribiżew

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According to regex101 the above pattern works in PHP, but doesn't in other programming languages (like e.g. Python) which are apparently missing some of the features and are not able to parse that pattern. – Claudio Nov 03 '22 at 21:04
1

@Claudio This pattern uses PCRE features (not only php). You can use that in Python too with https://pypi.org/project/regex/ – bobble bubble Nov 03 '22 at 21:17
1

@bobblebubble Yes, good to know that it works in Python when using the regex module. Just tested it and it works. – Claudio Nov 03 '22 at 21:57

Regular expression to match and remove unclosed parenthesis

2 Answers2