Regex to find matches from a string having multiple square brackets

Question

I have a paragraph like below:

Some wording for testing [!#today] where the [!condition] does not satisfy with this verbiage [!ShowElemIf://Student/FullName; [[[Text not recognized fully]]] ;/First Name] But simple tags found having age [!ShowElemIf://Student/Age;xml//Student/DOB/@formatted;y]

I need to find all the placeholders/tags from above which are like: [!tag] using C#. I tried for a regex but it is not able to find the tag having "FullName" word as highlighted in bold above.

List<string> tags = Regex.Matches(
                     sampleText.Replace(Environment.NewLine, ""), @"\[!([^]]+)\] ")
                     .Cast<Match>()
                     .Select(x => x.Groups[1].Value)
                     .ToList();

Using this RegEx I can find below but not the highlighted one.

today
condition
ShowElemIf://Student/Age;xml//Student/DOB/@formatted;y

Why do you have all that white space at the end of your pattern? — juharr, Mar 31 '17 at 12:30
@juharr: I believe it is a quirk of Visual Studio, I have seen it already at SO, and also got the same issue yesterday when pasting text into my VS. It is just a copy/paste issue. — Wiktor Stribiżew, Mar 31 '17 at 12:34
Yes. You may consider it as typo mistakes. Thanks@Wiktor for your answer. — sapatelbaps, Mar 31 '17 at 12:40

score 3 · Accepted Answer · answered Mar 31 '17 at 12:29

You need to use balancing groups available in .NET regex:

@"\[!((?:[^][]+|(?<o>\[)|(?<-o>)])*(?(o)(?!)))]"

See the regex demo

Details:

\[! - a [! substring
((?:[^][]+|(?<o>\[)|(?<-o>)])*(?(o)(?!))) - Capturing group 1 matching
- (?: - a non-capturing group with 3 alternatives:
  - [^][]+| - 1 or more chars other than [ and ], or
  - (?<o>\[)| - a [ pushed into "o" group stack, or
  - (?<-o>)] - a ] is subtracted from the "o" group stack
- )* - zero or more occurrences
- (?(o)(?!))) - a conditional construct checking if the "o" group stack is empty. If it is empty, matching goes on, else, no match is returned.
] - a literal closing ] symbol.

Regex to find matches from a string having multiple square brackets

1 Answers1