How to to transform x^(...) to x^{...} even when brackets are inside? Pure Regex possible?

Question

I need to change many posts and edit the content so that ^(...) becomes x^{...}.

What I have so far:

    $regexpattern = "/\^\((.*?)\)/";
    $replaceregex = "^{\$1}";

    $content_new = preg_replace($regexpattern, $replaceregex, $content);

which works.

However, I realized that if there is a round bracket inside the round wrapping brackets, it fails.

Example:

this should be transformed a^(x²) and this b^(-(x²))

becomes:

this should be transformed a^{x²} and this b^{-(x²})

Needed:

this should be transformed a^(x²) and this b^{-(x²)}

How can I prevent this and only replace the last bracket? Or do we need to use PHP and explode the content with ^(...) into Arrays and replace?

It could also be that there are multiple brackets inside (even if rare).

PS: After writing this question I found: https://stackoverflow.com/a/27052437/1066234 but there is no solution provided for this specific case.

Regular expressions typically have problems with all kinds of nested structures. — Some programmer dude, Nov 12 '18 at 08:15
What is expected output for `this should be transformed a^(x²) and this b^(-(x²))`? — anubhava, Nov 12 '18 at 08:22
this recursive expression https://regex101.com/r/Hlt37z/2 seems to work don't know if recursive expression are supported by preg_replace — Nahuel Fouilleul, Nov 12 '18 at 08:25

score 1 · Answer 1 · answered Nov 12 '18 at 08:36

You can use this recursive regex in PHP with a negative lookahead:

$str = 'this should be transformed a^(x²) and this b^(-(x²))';
$re = '/\^ ( \( ( (?: [^()]* | (?-2) )* ) \) ) (?!.*\^\()/x';
$repl = preg_replace($re, '^{$2}', $str);
//=> this should be transformed a^(x²) and this b^{-(x²)}

RegEx Demo

splash58 · Accepted Answer · 2018-11-12T09:14:42.470

1

Such regex matches only outter brackets

 \^(\((([^()]|(?1))*)\))

and replace with

^{$2}

demo on regex101

demo on sandbox

edited Nov 12 '18 at 09:14

answered Nov 12 '18 at 08:36

splash58

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OP wants to match `^` before `(` – anubhava Nov 12 '18 at 08:38
Worked nicely in my test: https://regex101.com/r/tMlAzv/10 (one line is a non-match on purpose) – Avatar Nov 12 '18 at 10:12
Glad to help! Good luck! – splash58 Nov 12 '18 at 10:13

How to to transform x^(...) to x^{...} even when brackets are inside? Pure Regex possible?

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