PHP Find specified variable within an external webpage

I have a variable that is being defined within my PHP script. It is merely a alphanumeric string.

I want the PHP to open a webpage that is external to this script and see if the value of my variable exists somewhere.

E.g.

$my_variable = "hello";

Miscellaneous (external) website:

This is our website, it is very brilliant and contains hello a lot of information!

I want the PHP script to check the website and see if the value of the variable exists. I was wondering how this could be done please.