using System;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
        String word = @"hello";
        String input = @"hello. I am a string. hello friend. Many hellos. hello .hello";
 
        Console.WriteLine("--- Input ---" + Environment.NewLine + input + Environment.NewLine);
        Console.WriteLine("--- Matches ---");
 
 
Regex regex = new Regex(@"(?<=\s)\b" + word + @"\b|\b" + word + @"\b(?=[\s\.])");
        MatchCollection mc = regex.Matches(input);
        foreach(Match m in mc)
        {
            Console.WriteLine(m.Value + " - " + m.Index.ToString());
        }
	}
}

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