How to match values ending with an optional string through Regex?

Question

I am trying to extract a first name from a text snippet, which optionally has a last name in the same line as: <first_name>name<last_name>

E.g.:

Text: JohnnameSnow -> Result: John
Text: John -> Result: John

So I want to extract the <first_name> part from that line, but if there is no name<last_name> it should return the full line.

I have tried the following Regex:

([A-zÀ-ÿ-]{2,})(?=(?:name))

That works fine if there's actually a last name in the same line, but does not return me the full line when there is not. Unfortunately the solution doesn't seem to be as easy as adding |$.

Can I look for an optional end word and ignore it if it does not occur?

Answer 1

You can use

^(?<first>\p{L}+?)(?:name(?<last>\p{L}+))?$

See the regex demo. Output:

Details

• ^ - start of string
• (?<first>\p{L}+?) - Group "first": one or more letters, but as few as possible
• (?:name(?<last>\p{L}+))? - an optional non-capturing group:
  • name - a substring
  • (?<last>\p{L}+) - Group "last": one or more letters
• $ - end of string.

See the C# demo:

var strings = new List<string> { "JohnnameSnow", "John" };
foreach (var s in strings)
{
    Console.WriteLine(s);
    var m = Regex.Match(s, @"^(?<first>\p{L}+?)(?:name(?<last>\p{L}+))?$");
    if (m.Success) 
    {
        Console.WriteLine("First name: {0}, Last name = {1}", m.Groups["first"].Value, m.Groups["last"].Value);
    }
    else
    {
        Console.WriteLine("No match!");
    }
}

Output:

JohnnameSnow
First name: John, Last name = Snow
John
First name: John, Last name =