What characters need to be escaped in .NET Regex?

Question

In a .NET Regex pattern, what special characters need to be escaped in order to be used literally?

Answer 1

I think you can get the list of chars as

List<char> chars = Enumerable.Range(0,65535)
                .Where(i=>((char)i).ToString()!=Regex.Escape(((char)i).ToString()))
                .Select(i=>(char)i)
                .ToList();

--

\t\n\f\r#$()*+.?[\^{|

Answer 2

Here is the list of characters that need to be escaped to use them as normal literals:

1. Opening square bracket [
2. Backslash \
3. Caret ^
4. Dollar sign $
5. Period or dot .
6. Vertical bar or pipe symbol |
7. Question mark ?
8. Asterisk or star *
9. Plus sign +
10. Opening round bracket ( and the closing round bracket )
11. Opening curly bracket {
12. Pound/Hash sign #

These special characters are often called "metacharacters".

But, I agree with Jon to use Regex.Escape instead of hardcoding these character in code.

Answer 3

See the MSDN documentation here: http://msdn.microsoft.com/en-us/library/az24scfc.aspx#character_escapes

The problem with a complete list is that it depends on context. For example . must be escaped, unless it is enclosed in brackets, as in [.]. ] technically does not need to be escaped, unless it is preceded by [. - has no special meaning, unless it's inside of brackets, as in [A-Z]. = has no special meaning unless it is preceded by ? as in (?=).

Answer 4

I don't know the complete set of characters - but I wouldn't rely on the knowledge anyway, and I wouldn't put it into code. Instead, I would use Regex.Escape whenever I wanted some literal text that I wasn't sure about:

// Don't actually do this to check containment... it's just a little example.
public bool RegexContains(string haystack, string needle)
{
    Regex regex = new Regex("^.*" + Regex.Escape(needle) + ".*$");
    return regex.IsMatch(haystack);
}