Find a string in a text file and add text at the beginning to that line in php
===

I have a text file:

John customerA <br>
Michael customerB <br>
Joe CustomerA<br>
Jacky CustomerC<br>

How to add 'active' string into the beginning of the text and only for 'customerA', so the output will be

active John customerA <br>
Michael customerB <br>
active Joe CustomerA <br>
Jacky CustomerC <br>

Thanks