I have a website built using HTML,JS,PHP. I use Linux OS and apache2 server and MySQL as a back end. To connect to the MySQL server I have created connection in each PHP page,But I want this connection string to be written in a single file(Like web.config in Visual studio),so that I can change the connection string easily whenever it is necessary.I have installed PHPMYADMIN and I can see couple of config files in that folder.But I do not know where I need to write this connection string? 

Or shall I create a PHP file with the connection string and include() this file in every other PHP files and create the instance of the connection?

I am not using any IDE for building the website.

Any help is greatly appreciated.

Thanks a lot.