using System;
using System.Text.RegularExpressions;
public class Example
{
    public static void Main()
    {
        string pattern = @"^(?![\S\s]*should not exist)";
        string input = @"This is a block of text
with many new lines
but in this block
some words should not exist
such as the line above this one";
        RegexOptions options = RegexOptions.IgnoreCase;
        
        Match m = Regex.Match(input, pattern, options);
        Console.WriteLine("'{0}' found at index {1}", m.Value, m.Index);
    }
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx