PHP regex, check for a lot of the same letter, continuously

Question

I want to prevent this kind of typing:

aaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbnonsense

for that I want to check that a certain letter gets repeated more than 9 times:

preg_match('/.{9,}/',$key)

but this would suit any word that has more than 9 letters in it, such as: supercalifregilisticexpealidocious

How do I do this?

Answer 1

You need a back reference to match the same character multiple times:

preg_match('/(.)\1{8}/', $string);