Poor man's php cache. Saves to files. Includes expiry.

php_cache.php

<?php

function add_cache($key, $value, $ttl) {
  $dir = __DIR__.'/../cache/';
  // Remove slashes for security
  $filename = $dir . str_replace('/', '', $key);
  // Store expiry in first line
  $lines = [(string)(time() + (int)$ttl), $value ];
  if (!file_exists($dir)) mkdir($dir, 0755, true);
  file_put_contents($filename, implode("\n", $lines));
}

function get_cache($key) {
  // Remove slashes for security
  $filename = __DIR__.'/../cache/'.str_replace('/', '', $key);
  if (file_exists($filename)) {
    $contents = file_get_contents($filename);
    $lines = explode("\n", $contents);
    $expiry = array_shift($lines);
    if (time() > (int)$expiry) {
      unlink($filename);
    } else {
      return implode("\n", $lines);
    }
  }
}