Brackets with dot, regular expressions

Question

I want delete brakets that ends on a dot from string. I use regular expresion - @"\([^)]+\)\." it works with string like this - some text (some text) some (text)., after regular expression I have string - some text (some text) some But this not work with string like that - some text (some text) some (text (text) some). How to fix it?

Answer 1

"How to fix it?" Traditional answer: You can't. Regular expressions do not support rested constructs. This is true for most regex dialects out there.

---

The .NET regular expression engine however supports balancing groups. With them you can identify and handle nesting.

To handle a nested construct, you must define its opening and closing pattern, in your case those are the parentheses ( and ), respectively.

• open: (?<paren>\()
• close: (?<-paren>\))

Think of this as a sort of counter named "paren" that counts up when it encounters ( and counts down when it encounters ) (internally, it's a bit different, but as a metaphor this is sufficient).

Now those two can be used to define the contents of a parenthesis, i.e

• either anything but a parenthesis: [^()]*
• or the opening pattern
• or closing pattern from above

or, in one expression: (?:[^()]*|(?<paren>\()|(?<-paren>\)))+

The entire regex should fail when the counter is not zero at the end, i.e. the parentheses are not balanced. To make that happen, the (?(paren)(?!)) construct is used (that's a conditional, designed to fail when there is an unmatched paren left).

Your finished expression looks like this (whitespace ignored)

\(
  (?:
    [^()]*
    |(?<paren>\()
    |(?<-paren>\))
  )+
  (?(paren)(?!))
\)\.$

See it live: http://regexhero.net/tester/?id=feb992a2-cc5d-497a-9d4a-a10317487e46

Recommended reading:

• What are regular expression Balancing Groups? here on SO (go read it, it's fantastic)
• MSDN: Grouping Constructs in Regular Expressions
• regular-expressions.info: Matching Nested Constructs with Balancing Groups
• Flagrant Badassery: Fun With .NET Regex Balancing Groups
• MSDN Blogs: Nested/Recursive Regex and .NET Balancing Groups

Answer 2

Just change your regex like below to match the brackets which ends with .

@"\((?:[^()]*\([^()]*\))*[^()]*\)\."

DEMO

Regular Expression:

\(                       '('
(?:                      group, but do not capture (0 or more
                         times):
  [^()]*                   any character except: '(', ')' (0 or
                           more times)
  \(                       '('
  [^()]*                   any character except: '(', ')' (0 or
                           more times)
  \)                       ')'
)*                       end of grouping
[^()]*                   any character except: '(', ')' (0 or more
                         times)
\)                       ')'
\.                       '.'