A file system based cache class.

file_cache.php

<?php
class file_cache
{
	private $root_dir;

	public function __construct($root_dir) {
		$this->root_dir = $root_dir;

		if (FALSE == file_exists($this->root_dir)) {
			mkdir($this->root_dir, 0700, true);
		}
	}

	public function set($key, $value) {
		$key = $this->escape_key($key);

		$file_name = $this->root_dir . '/' . $key;

		$dir = dirname($file_name);

		if (FALSE == file_exists($dir)) {
			mkdir($dir, 0700, true);
		}

		file_put_contents($file_name, serialize($value), LOCK_EX);
	}

	public function get($key) {
		$key = $this->escape_key($key);

		$file_name = $this->root_dir . '/' . $key;

		if (file_exists($file_name)) {
			return unserialize(file_get_contents($file_name));
		}

		return null;
	}

	public function remove($key) {
		$key = $this->escape_key($key);

		$file = $this->root_dir . '/' . $key;

		if (file_exists($file)) {
			unlink($file);
		}
	}

	public function remove_by_search($key) {
		$key = $this->escape_key($key);

		$dir = $this->root_dir . '/' . $key;

		if (strrpos($key, '/') < 0)
			$key .= '/';

		if (file_exists($dir)) {
			$this->remove_dir($dir);
		}
	}

	private function escape_key($key) {
		return str_replace('..', '', $key);
	}

	private function remove_dir($dirName) {
		$result = false;

		$handle = opendir($dirName);

		while(($file = readdir($handle)) !== false) {
			if($file != '.' && $file != '..') {
				$dir = $dirName . DIRECTORY_SEPARATOR . $file;

				is_dir($dir) ? $this->remove_dir($dir) : unlink($dir);
			}
		}

		closedir($handle);

		rmdir($dirName) ? true : false;

		return $result;
	}
}
?>

Example, cache in "/dev/shm":

$data_1 = array(
  'u_id' => 1,
  'name' => 'DaDa'
);

$data_2 = array(
  'u_id' => 2,
  'name' => 'WaWa'
);

$cache = new file_cache("/dev/shm");

$cache->set("user/1/data", $data_1);
$cache->set("user/2/data", $data_2);

$result = $cache->get("user/1/data");

$cache->remove("user/1/data");

$cache->remove_by_search("user", $data_1);  // remove all data under 'user' node