How can PHP developers ensure compatibility and functionality across different web hosting environments with varying restrictions on file system access?

PHP developers can ensure compatibility and functionality across different web hosting environments with varying restrictions on file system access by using PHP functions that do not rely on direct file system access, such as `file_get_contents()` and `file_put_contents()`. By using these functions instead of direct file system operations, developers can avoid issues related to file system restrictions. Additionally, developers can utilize PHP's built-in functions for handling file uploads and downloads to ensure compatibility across different hosting environments.

// Example code using file_get_contents() and file_put_contents() to read and write files
$file_contents = file_get_contents('example.txt');
file_put_contents('new_example.txt', $file_contents);