using System;   
using System.Text.RegularExpressions;
 
public class Test
{
    public static void Main()
    {
        var rx = new Regex(@"cgif.*\.txt$", RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.Singleline);
        bool x1=rx.IsMatch("abc\\cgif123.txt");
        Console.WriteLine($"{x1}"); // should return true
 
        bool x2=rx.IsMatch("abc\\cgif.txt");
        Console.WriteLine($"{x2}"); // should return true
 
        bool x3=rx.IsMatch("abc\\cgif.txtabc");
        Console.WriteLine($"{x3}"); // should return false
    }
}

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