Regex: Get anything between any curly braces

Question

Regex noob here

I have the following string:

This is a message {key1} {{key2}} {{{key3}}}, and includes {key4}.

I'm trying to extract anything between the outer curly braces. Expected matches:

key1
{key2}
{{key3}}
key4

Most SO examples cover matches on a single curly brace or a double curly brace, but not both or any variation of. Expressions like [^{\}]+(?=}) will get me the content between the inner braces, and (?<=\{).*?(?=\}) will get the leading braces except the first, but not the trailing ones.

Answer 1

You may get the results you need using

var results = Regex.Matches(text, @"{({*[^{}]*}*)}")
    .Cast<Match>()
    .Select(x => x.Groups[1].Value);

See the regex demo.

Regex details

• { - an open curly brace
• ({*[^{}]*}*) - Group 1:
  • {* - 0 or more open curly braces
  • [^{}]* - 0 or more chars other than curly braces
  • }* - 0 or more close curly braces
• } - a close curly brace

Bonus solution (provided in comments)

If you need to extract a string between nested curly braces you can use

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

See this regex demo. Here,

• \{ - matches a { char
• ((?>[^{}]+|(?<c>{)|(?<-c>}))*) - Group 1: zero or more repetitions of either one or more chars other than { and }, or a { char (pushed onto Group "c" stack) or a } char (popped off the Group "c" stack)
• (?(c)(?!)) - a check: if Group "c" still has a value on its stack, trigger backtracking (caused by "fail" with unconditional (?!) lookahead)
• } - a } char.

And if they can be overlapping:

(?=(\{((?>[^{}]+|(?<c>{)|(?<-c>}))*)(?(c)(?!))}))

Just get match.Groups[1].Value to get the whole match, or match.Groups[2].Value to get text inside braces only after you get a match.