Replace part of matched string with Regex.Replace

Question

Suppose I have string like this ".1.12.3.4.12.4."

As a result I would like to get ".01.12.03.04.12.04."

As you can see, I want all numbers of length == 1 to become of length == 2 with zero at the beginning. How can I achieve this?

Answer 1

Try this:

var input = ".1.12.3.4.12.4.";
var output = Regex.Replace(input, @"\.(\d)(?=\.)", ".0$1");
Console.WriteLine(output); // .01.12.03.04.12.04.

Answer 2

Split the string into tokens, format each resulting number and then join them back:

var input = ".1.12.3.4.12.4.";
var output = string.Join(
    ".", 
    input.Split('.')
         .Select(i => i.Length == 0 ? "" : i.PadLeft(2, '0'))
);

The best part of this solution is that you can easily change the length of the padded result.

Answer 3

You can do this

Regex.Replace(input,@"(?<=^|[.])(?=\d([.]|$))","0");

Answer 4

string result = string.Join(".", str.Split(".").Select(n => n.Length == 1 ? "0" + n : n));