正则表达式以查找3个方括号之间包含的字符串

Question

Could give a hand with this regex ?

\{{{(.*?)\}}}

It matches

{{{test1}}}
{{{{test4}}}
{{{test5}}}

I would like to match only {{{test1}}} and {{{test5}}} . There must be only 3 brackets on the left and right no, so {{{{test4}}} should be INVALID.

Answer 1

You need to restrict the delimiters with lookarounds:

(?<!{){{{(?!{)(.*?)(?<!})}}}(?!})
^^^^^^    ^^^^      ^^^^^   ^^^^^

See the regex demo

The (?<!{) is a negative lookbehind that fails the match if there is a { immediately to the left of the current location and (?!{) is a negative lookahead that fails the match immediately to the right of the current location. Similar constructs are used to set the context for the }}} trailing delimiter.

To exclude matching {{{....}}} substrings that contain either { or } , you need to replace the .*? (lazy dot matching pattern) with a *negated character class [^{}]* that will also make the (?!{) and (?<!{) lookarounds redundant in the above regex:

(?<!{){{{([^{}]*)}}}(?!})

See another regex demo , where {{{test{6}here}}} is not matched.

Usage to extract the values in between {{{ and }}} :

var results = Regex.Matches(s, @"(?<!{){{{([^{}]*)}}}(?!})")
    .Cast<Match>()
    .Select(m => m.Groups[1].Value)
    .ToList();

Answer 2

You can use this one : (?<!{){{3}[^{}]*}{3}(?!})

Explanation

{{3} starts with a { 3 times exactly

[^{}]* any character except { or }

}{3} ends with } 3 times exactly

Surrounded by negative lookbehind (?<!{) and negative lookahead (?!}) to make sure that the immediate preceding character will not be { and that the next immediate character will not be }