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Exam 70-536 study notes

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 regexes is Expresso.
  • There are many good tutorials around.

Good practice

  • Always include ^ and $ when validating input.
    • Without these you will simply check if a string contains the regex, which can expose a security vulnerability.
    • See the example below of what can happen when forgetting the leading ^.
  • Prefix your regex string with @ (a verbatim string) 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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