如何找到所有带有正则表达式的耦合支架？

Question

I'd like to have one regular expression to find all curly brackets and replace them with other strings.

For example, I want to replace " {foo} " with " FOO " and " {bar} " with " BAR " and " {} " with " EMPTY ". If the input is " abc {foo} def {bar} {} ", then the output is " abc FOO def BAR EMPTY ".

Nested brackets or un-coupled brackets are not allowed. If character "{" or "}" is necessary. It should be doubled. So, "{{ def }}" is just "{ def }".

Other string in {} is not allowed. Say, I just want " {foo} " and " {bar} ". So, " abc {xyz} def " should be recognized as invalid input.

Answer 1

If you have negative lookbehinds/lookaheads available:

(?<!{){([a-z]+)}(?!})

and replace with the value of the matching group.

The ([az]+) matches your contained character string, the (?<!{) makes sure there isn't a second { before your { , and the (?!}) makes sure there isn't a second } after your } .

If you don't have lookbehinds/lookaheads, then

(?^|[^{]){([a-z]+)}(?$|[^})

Answer 2

I would first go and replace {} with EMPTY without using a regular expression.

Then use

(?<!{){(foo|bar)}(?!})

to match {foo} or {bar} but not {} or {{anything}} or {anything}

Backreference no. 1 contains the matched text.

So a code snippet could look like

Regex matches = new Regex(@"(?<!\{)\{(foo|bar)\}(?!\})", RegexOptions.IgnoreCase);
resultString = matches.Replace(subjectString, "$1".ToUpper());

(I hope that calling ToUpper() on a string works; I don't know C#, so please correct me if I'm wrong)