新建Log.class.php，复制以下代码放入其中：

<?php
interface ILogHandler {
    public function write($msg);
}

// PHP日志类
class CLogFileHandler implements ILogHandler {
    private $handle = null;

    public function __construct($file = '') {
        $this->handle = fopen($file, 'a');
    }

    public function write($msg) {
        fwrite($this->handle, $msg, 4096);
    }

    public function __destruct() {
        fclose($this->handle);
    }
}
class Log {
    private $handler = null;
    private $level = 15;

    private static $instance = null;

    private function __construct() {
    }
    private function __clone() {
    }

    public static function Init($handler = null, $level = 15) {
        if (!self::$instance instanceof self) {
            self::$instance = new self();
            self::$instance->__setHandle($handler);
            self::$instance->__setLevel($level);
        }
        return self::$instance;
    }


    private function __setHandle($handler) {
        $this->handler = $handler;
    }

    private function __setLevel($level) {
        $this->level = $level;
    }

    public static function DEBUG($msg) {
        self::$instance->write(1, $msg);
    }

    public static function WARN($msg) {
        self::$instance->write(4, $msg);
    }

    public static function ERROR($msg) {
        $debugInfo = debug_backtrace();
        $stack = "[";
        foreach ($debugInfo as $key => $val) {
            if (array_key_exists("file", $val)) {
                $stack .= ",file:" . $val["file"];
            }
            if (array_key_exists("line", $val)) {
                $stack .= ",line:" . $val["line"];
            }
            if (array_key_exists("function", $val)) {
                $stack .= ",function:" . $val["function"];
            }
        }
        $stack .= "]";
        self::$instance->write(8, $stack . $msg);
    }

    public static function INFO($msg) {
        self::$instance->write(2, $msg);
    }

    private function getLevelStr($level) {
        switch ($level) {
            case 1:
                return 'debug';
                break;
            case 2:
                return 'info';
                break;
            case 4:
                return 'warn';
                break;
            case 8:
                return 'error';
                break;
            default:
        }
    }

    protected function write($level, $msg) {
        if (($level & $this->level) == $level) {
            $msg = '[' . date('Y-m-d H:i:s') . '][' . $this->getLevelStr($level) . '] ' . $msg . "\n";
            $this->handler->write($msg);
        }
    }
}

调用方式：

<?php
require 'Log.class.php'; // 导入日志类文件
define('DS', DIRECTORY_SEPARATOR); // 设置目录分隔符
define('LOG_PATH', dirname(__FILE__) . DS . 'log' . DS); // 日志文件目录

$logHandler = new CLogFileHandler(LOG_PATH . date('Y-m-d') . '.log');
$log = Log::Init($logHandler, 15);

Log::DEBUG('111111');