Replace chars if not match

Question

I'm looking for a regular expression that removes illegal characters. But I don't know what the characters will be.

For example:

In a process, I want my string to match ([a-zA-Z0-9/-]*). So I would like to replace all characters that don't match the regexp above.

Answer 1

That would be:

[^a-zA-Z0-9/-]+

[^ ] at the start of a character class negates it - it matches characters not in the class.

See also: Character Classes

Answer 2

Thanks to Kobi's answer I've created a helper method to strips unaccepted characters .

The allowed pattern should be in Regex format, expect them wrapped in square brackets. A function will insert a tilde after opening squere bracket. I anticipate that it could work not for all RegEx describing valid characters sets,but it works for relatively simple sets, that we are using.

               /// <summary>
               /// Replaces  not expected characters.
               /// </summary>
               /// <param name="text"> The text.</param>
               /// <param name="allowedPattern"> The allowed pattern in Regex format, expect them wrapped in brackets</param>
               /// <param name="replacement"> The replacement.</param>
               /// <returns></returns>
               /// //        https://stackoverflow.com/questions/4460290/replace-chars-if-not-match.
               //https://stackoverflow.com/questions/6154426/replace-remove-characters-that-do-not-match-the-regular-expression-net
               //[^ ] at the start of a character class negates it - it matches characters not in the class.
               //Replace/Remove characters that do not match the Regular Expression
               static public string ReplaceNotExpectedCharacters( this string text, string allowedPattern,string replacement )
              {
                     allowedPattern = allowedPattern.StripBrackets( "[", "]" );
                      //[^ ] at the start of a character class negates it - it matches characters not in the class.
                      var result = Regex.Replace(text, @"[^" + allowedPattern + "]", replacement);
                      return result; //returns result free of negated chars
              }