using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
 
		var entities= new List<string>(){"101", "102", "103",}; 
		var files= new List<string>(){"101_F05_20101001.csv", "102_F05_20101001.csv", "201_F05_20101001.csv", "202_F05_20101001.csv"};
 
		var pat = $@"^(?:{string.Join("|", entities)})_F05_\d*\.csv$";
		//Console.WriteLine(pat);
		var list = files
			.Where(x => Regex.IsMatch(x, pat))
		    .ToList();
 
		foreach (var s in list) {
			Console.WriteLine(s);
		}
	}
}

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