using System;
using System.Text.RegularExpressions;
public class Test
{
public static void Main()
{
string temp = @"\folder_name\file_name.filetype.[somename@somedomain].wallet";
var m = Regex.Match(temp, @"(?<=\\)[^.]*\.[^.]*(?=\.\[[^\]]*\].wallet)");
if (m.Success) {
Console.WriteLine(m.Value);
} else {
Console.WriteLine("<no match>");
}
}
}
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