Question

I’ve spent hours and hours trying to solve this.

Here is my Regex string:
^(?=.{4})(?!.{32})[a-zA-Z0-9_]+((\.(-\.)*-?|-(\.-)*\.?) [a-zA-Z0-9_]+)*$ –
You can test it here

Here is what I tried to acomplish (username validation):

1. string length range -> OK
2. letters, numbers, _ – . allowed (- and . disallowed at begining and or end of username) -> OK
3. need to prevent repeated characters (over 5 characters in line) -> need help!

Answer 1

This:

^(?=.{4})(?!.{32})(?!.*(.)\1{4})\w[\w.-]+\w$

Use another (negative) lookahead to take care of the third condition. This one will make sure that there is no character, that is followed by itself 4 times.

I also simplified your character classes by using \w which represents [a-zA-Z0-9]. Also, as F.J pointed out, you can combine the first two lookaheads into one:

^(?=.{4,31}$)(?!.*(.)\1{4})\w[\w.-]+\w$