Overlapping Regex Replace

Question

I have a situation where commas are stripped when they shouldn't be, e.g.,

John 3:16,18,4:2 becomes John 3:16 18 4:2

I would like to put the commas back, and thought I could do it with

string strRegex = @"(\d+)\s+(\d+)";
RegexOptions myRegexOptions = RegexOptions.None;
Regex myRegex = new Regex(strRegex, myRegexOptions);
string strTargetString = @"John 3:16 17 4:3";
string strReplace = @"$1,$2";

return myRegex.Replace(strTargetString, strReplace);

but this just gives me

John 3:16,18 4:2

What am I missing?

Answer 1

You can try something with lookbehind:

@"(?<=\d)\s+(\d+)"

and replace with

,$1

Answer 2

Use a lookbehind and lookahead so the digits are not a part of your match:

string strRegex = @"(?<=\d)\s+(?=\d)";
...
string strReplace = @",";