Regex Select “..” And not “…”

Question

Essentially I have a string: string str = "Hello.... My name is Steve.. I like Dogs."

I need to change occurrences of "..." or more periods into just 3. Any occurrences of 2 need to become 1.

Using

Regex.Replace(str)

Regex.Replace(str,"[.]{3,}","...") works great at changing the groups greater then 3 to 3. But I can't select groups of 2 "[.]{2}" because the groups of 3 are made up of 2...

My final String needs to look like this: string str = "Hello... My name is Steve. I like Dogs."

Answer 1

If you are allowed to use c# features:

string input = "Hello.... My name is Steve.. I like Dogs.";
string output = Regex.Replace(input, @"\.{2,}", m => m.Length == 2 ? "." : "...");

Answer 2

正则表达式具有负的前瞻性和后瞻性：

(?<!\.)\.\.(?!\.)