[RESOLVED] Detecting repeating strings

[Distortion]

I'm going to classically preface this by saying that I'm new PHP and, obviously, need some help. I've searched around some and haven't come to any real solution. I'm sure it's probably out there and I just haven't found it yet, but I decided to post here in hopes that someone could just help me.

Like the title says, I'm looking for some guidance when it comes to how to detect repeating strings of text. Incase you're wondering, the strings in question here are dynamic and aren't one specific type.

For example, if I were to, say, type "12121212121212121212" or "" I'm looking for a way to detect that there's a large number of repeating characters or sequence of characters and after X amount replace the excess ones with something else. I'm fairly confident that I can replace them, I just need a way to detect the repeating string of characters.

Hopefully that makes sense. Thanks in advance.