Get what PHP has output so far as a string

To get what PHP has output so far as a string you need to make use of output buffering. Switching on output buffering tells PHP top stop sending data to the browser piecemeal. Instead, you can fetch it manually.

Once the script terminates, PHP will send whatever is in the output buffer to the browser.

The output buffer is managed with the ob_ functions. Here’s an example:

// Start OB
ob_start();

// echo whatever you want
// ...

$html = ob_get_contents();

// Do what you want with $html E.g.
file_put_contents('./cache/index.html', $html);