using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"#(?!(?:hashtag|DoNotRemoveThis)\b)[\w-]+(?=(?:\s+#[\w-]+)*\s*$)";
string substitution = @"";
string input = @"Any #hashtag in the middle of the string should NOT be removed regardless of what it is, for example #DoNotRemoveThis #KeepThisHashtag and any hashtag at the end of the string should be removed UNLESS it matches the exeptions in the regex. #deletethis #DoNotRemoveThis #thismustgoaway";
RegexOptions options = RegexOptions.IgnoreCase | RegexOptions.CultureInvariant;
Regex regex = new Regex(pattern, options);
string result = regex.Replace(input, substitution);
}
}
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