Regex for alphanumeric password, with at least 1 number and character

Question

Need help with a regex for alphanumeric password, with at least 1 number and character, and the length must be between 8-20 characters.

I have this but doesn't seem to be working (it doesn't have length requirements either):

^[A-Za-z0-9]*[A-Za-z][A-Za-z0-9]*$

Answer 1

^(?=.{8,20}$)(?=.*[0-9])(?=.*[a-zA-Z]).*

? :)

Answer 2

Wouldn't it be better to do this validation with some simple string functions instead of trying to shoehorn a difficult to validate regex into doing this?

Answer 3

If you take a look at this MSDN link, it gives an example of a password validation RegEx expression, and (more specifically) how to use it in ASP.NET.

For what you're looking to accomplish, this should work:

    (?!^[0-9]*$)(?!^[a-zA-Z]*$)^([a-zA-Z0-9]{8,20})$

This requires at least one digit, at least one alphabetic character, no special characters, and from 8-20 characters in length.

Answer 4

Something like this will be closer to your needs. (I didn't test it, though.)

Regex test = new Regex("^(?:(?<ch>[A-Za-z])|(?<num>[9-0])){8,20}$");
Match m = test.Match(input);
if (m.Success && m.Groups["ch"].Captures.Count > 1 && m.Groups["num"].Captures.Count > 1)
{
  // It's a good password.
}

Answer 5

Why not just use a handful of simple functions to check?

checkPasswordLength( String password);
checkPasswordNumber( String password);

Maybe a few more to check for occurrences of the same character repeatedly and consecutively.