Regex get the text after the match which must be the last occurrence

Question

I want to extract the string after the last occurrence of "cn=" using regex in C# application. So what I need is the string between last occurence of "cn=" and \ character Please note that the source string may contains spaces.

Example:

ou=company\ou=country\ou=site\cn=office\cn=name\ou=pet

Result:

name

So far Ive got (?<=cn=).* for selecting the text after the cn= using positive lookbehind and (?:.(?!cn=))+$ for finding the last occurence but I dont know how to combine it together to get desired result.

Answer 1

You may try using the following regex ...

(?m)(?<=cn=)[\w\s]+(?=\\?(?:ou=)?[\w\s]*$)

see regex demo

C# ( demo )

using System;
using System.Text.RegularExpressions;

public class RegEx
{
    public static void Main()
    {
        string pattern = @"(?m)(?<=cn=)[\w\s]+(?=\\?(?:ou=)?[\w\s]*$)";
        string input = @"ou=company\ou=country\ou=site\cn=office\cn=name\ou=pet";

        foreach (Match m in Regex.Matches(input, pattern))
        {
            Console.WriteLine("{0}", m.Value);
        }
    }
}

Answer 2

You could use a negative lookahead:

cn=(?!.*cn=)([^\\]+)

Take group $1 and see a demo on regex101.com. As full C# code, see a demo on ideone.com.

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To only have one group, add another lookaround:

(?<=cn=)(?!.*cn=)([^\\]+)