Inserting Files in PHP

Let's say we have one file:

index.php<?php
  echo 'index';
?>

Let's also say there is a second file:

test.php<?php
  echo 'test';
?>

Let's insert the contents of the second file into the first one. This is done using the include operator:

index.php<?php
  include 'test.php';
  echo 'index';
?>

The same file can be inserted any number of times:

index.php<?php
  include 'test.php';
  include 'test.php';
  include 'test.php';
  
  echo 'index';
?>