Regular expression for password validation in c#

Regular expression for password validation in c#

A common pattern for password validation in C# often includes requirements like a minimum length, at least one uppercase letter, at least one lowercase letter, at least one digit, and possibly special characters. Here's an example of a regular expression that enforces such criteria:

using System; using System.Text.RegularExpressions; class Program { static void Main() { string password = "Abcd123!"; // Define the regular expression for password validation string regexPattern = @"^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$"; // Create a Regex object Regex regex = new Regex(regexPattern); // Test if the password matches the pattern bool isMatch = regex.IsMatch(password); Console.WriteLine(isMatch); // true } }

Explanation of the regular expression:

  • ^: Asserts the start of the string.
  • (?=.*[a-z]): Positive lookahead for at least one lowercase letter.
  • (?=.*[A-Z]): Positive lookahead for at least one uppercase letter.
  • (?=.*\d): Positive lookahead for at least one digit.
  • (?=.*[@$!%*?&]): Positive lookahead for at least one special character (you can customize the set of special characters).
  • [A-Za-z\d@$!%*?&]{8,}: Matches a string containing at least 8 characters, consisting of letters (uppercase and lowercase), digits, and the specified special characters.
  • $: Asserts the end of the string.

Examples

  1. Password with Minimum Length Requirement:

    • "Regex pattern for password with minimum length requirement"
    • Code:
      ^.{8,}$
    • Description: Ensures the password has a minimum length of 8 characters.

  2. Password with Uppercase and Lowercase Letters:

    • "Regex pattern for password with uppercase and lowercase letters"
    • Code:
      ^(?=.*[a-z])(?=.*[A-Z]).+$
    • Description: Requires at least one lowercase and one uppercase letter in the password.

  3. Password with Numbers:

    • "Regex pattern for password with numbers"
    • Code:
      ^.*\d.*$
    • Description: Ensures the password contains at least one numeric digit.

  4. Password with Special Characters:

    • "Regex pattern for password with special characters"
    • Code:
      ^.*[^a-zA-Z\d].*$
    • Description: Requires at least one special character in the password.

  5. Password without Spaces:

    • "Regex pattern for password without spaces"
    • Code:
      ^\S+$
    • Description: Ensures the password does not contain any whitespace.

  6. Password with Specific Special Characters:

    • "Regex pattern for password with specific special characters"
    • Code:
      ^.*[!@#$%^&*()].*$
    • Description: Requires at least one of the specified special characters in the password.

  7. Password with Alphanumeric Characters:

    • "Regex pattern for password with alphanumeric characters"
    • Code:
      ^[a-zA-Z\d]+$
    • Description: Allows only alphanumeric characters in the password.

  8. Password with Specific Length Range:

    • "Regex pattern for password with specific length range"
    • Code:
      ^.{8,12}$
    • Description: Requires the password to be between 8 and 12 characters long.

  9. Password with Complex Requirements:

    • "Regex pattern for password with complex requirements"
    • Code:
      (?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[^a-zA-Z\d]).{8,}
    • Description: A more complex pattern requiring lowercase, uppercase, numeric, and special characters in the password.

  10. Password with Forbidden Substrings:

    • "Regex pattern for password with forbidden substrings"
    • Code:
      ^(?!.*password|admin|user).*$
    • Description: Ensures the password does not contain forbidden substrings like "password," "admin," or "user."

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