Regex Class
Part of my 2008 study notes for exam 70-536 (.NET Framework 2.0).
Overview
- Used to work with regular expressions.
- A good free tool to read and create regexs is Expresso.
- There are many good tutorials around.
Good practice
- Always include the ^ and $ when matching expressions.
- Without these you will simply check if a string contains the regex, which can expose a security vulnerability.
- See the example below for an example on what can happen when forgetting the leading ^.
- Start your regex with the @ sign for readability, instead of having to escape backslashes.
Examples
Checking Input
string regex = @"^\d{5}$";
Console.WriteLine(Regex.IsMatch("12345", regex) ? "Matches!" : "No match");
Console.WriteLine(Regex.IsMatch("1234", regex) ? "Matches!" : "No match");
Console.WriteLine(Regex.IsMatch("DROP DATABASE YourApp; -- 12345", @"\d{5}$") ? "Matches!" : "No match");
Replacing Input
string input = "The dog ate a bone.";
string regex = @"^The (?<animal>\w+)\b ate (?<food>.+)\.$";
Console.WriteLine(Regex.Replace(input, regex, "Animal: ${animal}, Food: ${food}"));
Using Groups
Match x = Regex.Match("Wim", "(?<FirstLetter>.).*");
Console.WriteLine(x.Groups["FirstLetter"]);
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