Question

I have the following code to parse by Regex:

        const string patern = @"^(\p{L}+)_";
        var rgx = new Regex(patern);
        var str1 = "library_log_12312_12.log";
        var m = rgx.Matches(str1);

It returns only one match and it is “library_”. I have read a lot of resources and it should not contain underscore, should it?

Answer 1

Your pattern includes the _, so the match does too. If you only want the group, you need to specify that. It’ll be in group 1 (as group 0 is always the whole match):

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main(string[] args)
    {
        var regex = new Regex(@"^(\p{L}+)_");
        var input = "library_log_12312_12.log";
        var matches = regex.Matches(input);
        var match = matches[0];
        Console.WriteLine(match.Groups[0]); // library_
        Console.WriteLine(match.Groups[1]); // library
    }
}