Regular Expression to match outer brackets

2018-06-27 11:11:53

I need a regular expression to select all the text between two outer brackets.

Example: some text(text here(possible text)text(possible text(more text)))end text

Result: (text here(possible text)text(possible text(more text)))

I've been trying for hours, mind you my regular expression knowledge isn't what I'd like it to be :-) so any help will be gratefully received.

Regular expressions are the wrong tool for the job because you are dealing with nested structures, ie recursion.

But there is a simple algorithm to do this, which I described in this answer to a previous question.

你可以使用正则表达式递归：

(([^()]|(?R))*)

I want to add this answer for quickreference. Feel free to update.

.NET Regex using balancing groups.

((?>((?<c>)|[^()]+|)(?<-c>))*(?(c)(?!)))

Where c is used as the depth counter.

Demo at Regexstorm.com

Stack Overflow : Using RegEx to balance match parenthesis

Wes' Puzzling Blog : Matching Balanced Constructs with .NET Regular Expressions

Greg Reinacker's Weblog : Nested Constructs in Regular Expressions

PCRE using a recursive pattern.

((?>[^)(]+|(?R))*)

Demo at regex101; Or without alternation:

((?>[^)(]*(?R)?)*)

Demo at regex101. The pattern is pasted at (?R) which represents (?0) .

Perl, PHP, Notepad++, R: perl=TRUE, Python: Regex package with (?V1) for Perl behaviour.

Ruby using subexpression calls.

With Ruby 2.0 g<0> can be used to call full pattern.

((?>[^)(]+|g<0>)*)

Demo at Rubular; Ruby 1.9 only supports capturing group recursion:

(((?>[^)(]+|g<1>)*))

Demo at Rubular (atomic grouping since Ruby 1.9.3)

JavaScript API :: XRegExp.matchRecursive

XRegExp.matchRecursive(str, '(', ')', 'g');

JS, Java and other regex flavors without recursion up to 2 levels of nesting:

((?:[^)(]+|((?:[^)(]+|([^)(]*))*))*)

Demo at regex101. Deeper nesting needs to be added to pattern.
To fail faster on unbalanced parenthesis drop the + quantifier.

Java : An interesting idea using forward references by @jaytea.

Reference - What does this regex mean?

rexegg.com - Recursive Regular Expressions

Regular-Expressions.info - Regular Expression Recursion

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