C# Regular Expression

Question

I can't seem to get this to work.

I am looking for a regular expression that will validate a password. Allowable characters are a-zA-Z0-9, but the sequence must have at least 1 number and 1 capital letter.

Can this be done?

Answer 1

^(?=.*[A-Z])(?=.*[0-9])[A-Za-z0-9]+$

should do.

^             # start of string 
(?=.*[A-Z])   # assert that there is at least one capital letter ahead
(?=.*[0-9])   # assert that there is at least one digit ahead
[A-Za-z0-9]+  # match any number of allowed characters 
              # Use {8,} instead of + to require a minimum length of 8 characters.
$             # end of string

Answer 2

You can use non-zero-width lookahead/lookbehind assertions in regex. For instance:

^\w*(?=\w*\d)(?=\w*[a-z])(?=\w*[A-Z])\w*$

Requires that there exist at least one number, one lowercase and one uppercase letter. Using \w allows you to accept non-English or accented characters (which you may or may not want to allow). Otherwise use [a-zA-Z] instead.

Answer 3

This is very close:

http://stackoverflow.com/questions/1051989/regex-for-alphanumeric-but-at-least-one-character

Answer 4

bool valid =  
    Regex.IsMatch(password, @"\w+")// add additional allowable characters here
    && Regex.IsMatch(password, @"\d")
    && Regex.IsMatch(password, @"\p{Lu}");