How to replace a link break (&#xa) with a comma using Regex

Question

One of our clients have asked us to replace the first line break (&#xa) with a comma.

So far the regex that we have for our location address is this:

Location = vacancy.Location.IsNullOrEmpty() ?
        string.Empty :
        Regex.Replace(vacancy.Location, "&#?[a-z0-9]+;", " ");

Can someone tell me how i can add another rule to the regex pattern which would replace only the first instance of &#xa with a comma?

Thank you!

Answer 1

To answer your question specifically: Regex.Replace(vacancy.Location, "(?<!&#xa;.*)&#xa;", ", "), where (?<!&#xa;.*) is a negative lookbehind assertion.

However, my recommendation is to avoid regex in favor of more readable methods such as:

ReplaceFirstOccurrence(vacancy.Location, "
", ", ");

private static string ReplaceFirstOccurrence(string source, string find, string replace)
{
    int firstOccurrenceIndex = source.IndexOf(find);

    if (firstOccurrenceIndex < 0)
    {
        return source;
    }

    string resultAfterRemoval = source.Remove(firstOccurrenceIndex, find.Length);
    string resultAfterInsertion = resultAfterRemoval.Insert(firstOccurrenceIndex, replace);

    return resultAfterInsertion;
}