404 Page in a File-Based PHP Engine

If a user enters an incorrect URL into the address bar, we must show an error page. Let the content of the error page be stored in a corresponding file:

view/404.php<div>
  page not found
</div>

To determine the incorrectness of a request, we need to check the existence of the content file corresponding to the requested URL:

index.php<?php
  $path = 'view' . $url . '.php';
  
  if (file_exists($path)) {
    // file exists
  } else {
    // file does not exist
  }
?>

Let's serve the content file if it exists, and the error file if there is no content:

index.php<?php
  $path = 'view' . $url . '.php';
  
  if (file_exists($path)) {
    $content = file_get_contents($path);
  } else {
    $content = file_get_contents('view/404.php');
  }
?>

In case of an error, we must send a header with a 404 error to the browser to explicitly indicate that the page was not found. Let's do that:

index.php<?php
  $path = 'view' . $url . '.php';
  
  if (file_exists($path)) {
    $content = file_get_contents($path);
  } else {
    header('HTTP/1.0 404 Not Found');
    $content = file_get_contents('view/404.php');
  }
?>