Question

I want to replace hyphen character with space if it is NOT enclosed by digits on both sides.

 string str = "Hefer 789-567 dfg-5mh";
            str = Regex.Replace(str, @"[a-zA-Z]\-(\d+)", "$1");

Output

Hefer 789-567 df5mh

Desired output

Hefer 789-567 dfg 5mh

Answer 1

The problem you are describing in your title can be solved using this:

Regex.Replace(str, @"(?<=[A-Za-z])-", " ");

The problem you are describing in the body of your question can be solved using this:

Regex.Replace(str, @"(?<!\d)-|-(?!\d)", " ");

Or without lookaround:

Regex.Replace(str, @"([^\d])-|-([^\d])", "$1 $2");