How to make a text search script on the page of someone else's site, if the text is found, then redirect to the desired page of your own?

Question

PHP

A person enters his login on Instagram, gets to the page as in the screenshot, where the subscribe button sends instas to the account for subscription, and if the person is subscribed by clicking on the "I subscribed" button, the script checks if there is such a person in the subscribers, and redirects to the page which one is needed with "chupa-chups" if not, then it writes you are not in the subscriptions, subscribe and gives a button to go to the insta account. the button click script should download all the content of the followers https://www.instagram.com/gladyshef/followers/ and search the list. Ready to thank for the finished result

Answer 1

Apparently, you need to load the page into some variable, and then parse it with regex's.
But in general, Instagram/FaceBook/VKontakte/etc has its own API - it's more correct to work through it.