I want a regular expression which masks first and last characters of a string with * if string lengt-CodePudding

I want a regular expression that masks first and last characters of a string with * if the string length is less than or equal to 4

Example :

abc --> *b*

abcd --> *bc*

What I have tried so far:

(?!^.?).(?!.{0}$)

CodePudding user response：

        var str = "a";
        var result = str.Length <= 2 ? "*" : (str.Length <= 4 ? "*" str.Substring(1, str.Length-2) "*": str);
        Console.WriteLine(result);

CodePudding user response：

^.(?=.{0,3}$)|(?<!.{4}).$

will match the first characters if only up to 3 characters come after it until the string ends,
and it will only match the last character if there are not 4 or more characters before it

I'm not sure if C# of .net core 3.1 supports look-behind expressions. If not then this may not work.