Regular Expression to Replace Specific character between 2 immediate letters or numbers?

Hello my friend:

I am writing a Text file to CSV Script but I want to remove all embedded commas, meaning commas between words or letters:

For example: I want to change this: "Daft Punk, is great" to "Daft Punk - is great"
So if my text file looks like this: "Daft Punk, is great", "yes! they are, great"

Then the result will look like this:"Daft Punk - is great", "yes! they are - great"

I do not know much about Regex. But is there a Regex that I can add to my code below to replace any comma that is between two letters?



More Examples:



"A B C D, E F G" or "A B C D,E F G" would turn to this: "A B C D - E F G"

Here is my code:

static void TextToCSV(string s, TextWriter writer)
        {
            foreach (var line in s.Replace(", ", "").Split(new string[] { Environment.NewLine}, StringSplitOptions.None))
            {   
                foreach (var t in line)
                {
                    writer.Write(t);
                }
                writer.WriteLine();
            }
            writer.Flush();
        }

        static void Main(string[] args)
        {
            TextReader reader = new StreamReader(@"C:\myfolder\sample.txt");
            string a = reader.ReadToEnd();
            reader.Close();

            FileStream aFile = new FileStream(@"C:\myfolder\sample.csv", FileMode.Create);
            
            TextToCSV(a, new StreamWriter(aFile));
            aFile.Close();
        }

Thanks everyone!