Read file to another server

file_put_contents() is a basic PHP function. It is not CodeIgniter's function.
CodeIgniter is build on PHP, so you can use PHP functions,
and you should know PHP.

Also, you can improve the user guide. Because CodeIgniter is made by contributions.
https://codeigniter4.github.io/CodeIgnit...quest.html
You can see "Edit this page" in right of the top.

ci-phpunit-test | CodeIgniter Testing Guide | CodeIgniter 3 to 4 Upgrade Helper