[Solved] Regex to remove all special characters from string?

I’m completely incapable of regular expressions, and so I need some help with a problem that I think would best be solved by using regular expressions.

I have list of strings in C#:

List<string> lstNames = new List<string>();

foreach (string n in lstNames) {
  // logic goes here that somehow uses regex to remove all special characters
  string regExp = "NO_IDEA";
  string tmp = Regex.Replace(n, regExp, "");

I need to be able to loop over the list and return each item without any special characters. For example, item one would be “TRA9423”, item two would be “TRA42101” and item three would be TRA109AD.

Is there a regular expression that can accomplish this for me?

Also, the list contains more than 4000 items, so I need the search and replace to be efficient and quick if possible.

I should have specified that any character beside a-z, A-Z and 0-9 is special in my circumstance.

Enquirer: Jagd


Solution #1:

It really depends on your definition of special characters. I find that a whitelist rather than a blacklist is the best approach in most situations:

tmp = Regex.Replace(n, "[^0-9a-zA-Z]+", "");

You should be careful with your current approach because the following two items will be converted to the same string and will therefore be indistinguishable:

Respondent: Mark Byers

Solution #2:

This should do it:


Basically it matches all non-alphanumeric characters.

Respondent: Daniel Egeberg

Solution #3:

[^a-zA-Z0-9] is a character class matches any non-alphanumeric characters.

Alternatively, [^wd] does the same thing.


string regExp = "[^wd]";
string tmp = Regex.Replace(n, regExp, "");
Respondent: MikeD

Solution #4:

You can use:

string regExp = "W";

This is equivalent to Daniel’s “[^a-zA-Z0-9]

W matches any nonword character. Equivalent to the Unicode categories [^p{Ll}p{Lu}p{Lt}p{Lo}p{Nd}p{Pc}].

Respondent: Dan Diplo

Solution #5:

Depending on your definition of “special character”, I think “[^a-zA-Z0-9]” would probably do the trick. That would find anything that is not a small letter, a capital letter, or a digit.

Respondent: Jay

Solution #6:

tmp = Regex.Replace(n, @"W+", "");

w matches letters, digits, and underscores, W is the negated version.

Respondent: Paul Creasey

Solution #7:

For my purposes I wanted all English ASCII chars, so this worked.

html = Regex.Replace(html, "[^x00-x80]+", "")
Respondent: BobC

Solution #8:

If you don’t want to use Regex then another option is to use


You can use this to loop through each char of the string and only return if true.

Respondent: Demarily

Solution #9:

public static string Letters(this string input)
    return string.Concat(input.Where(x => char.IsLetter(x) && !char.IsSymbol(x) && !char.IsWhiteSpace(x)));
Respondent: mattylantz

The answers/resolutions are collected from stackoverflow, are licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0 .

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