'log' => 'daily'

#config/app.php:111
'log' => env('APP_LOG', 'single'),

#vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php:36
protected $bootstrappers = [
    'Illuminate\Foundation\Bootstrap\DetectEnvironment',
    'Illuminate\Foundation\Bootstrap\LoadConfiguration',
    'Illuminate\Foundation\Bootstrap\ConfigureLogging',
    'Illuminate\Foundation\Bootstrap\HandleExceptions',
    'Illuminate\Foundation\Bootstrap\RegisterFacades',
    'Illuminate\Foundation\Bootstrap\RegisterProviders',
    'Illuminate\Foundation\Bootstrap\BootProviders',
];
<?php
namespace Illuminate\Foundation\Bootstrap;
use Illuminate\Log\Writer;
use Monolog\Logger as Monolog;
use Illuminate\Contracts\Foundation\Application;
class ConfigureLogging
{
/**
 * Bootstrap the given application.
 *
 * @param \Illuminate\Contracts\Foundation\Application $app
 * @return void
 */
public function bootstrap(Application $app)
{
  $log = $this->registerLogger($app);
  // If a custom Monolog configurator has been registered for the application
  // we will call that, passing Monolog along. Otherwise, we will grab the
  // the configurations for the log system and use it for configuration.
  if ($app->hasMonologConfigurator()) {
    call_user_func(
      $app->getMonologConfigurator(), $log->getMonolog()
    );
  } else {
    $this->configureHandlers($app, $log);
  }
}

protected function configureHandlers(Application $app, Writer $log)
{
    $method = 'configure'.ucfirst($app['config']['app.log']).'Handler';
    $this->{$method}($app, $log);
}
/**
* Configure the Monolog handlers for the application.
*
* @param \Illuminate\Contracts\Foundation\Application $app
* @param \Illuminate\Log\Writer $log
* @return void
*/
protected function configureSingleHandler(Application $app, Writer $log)
{
     $log->useFiles(
       $app->storagePath().'/logs/laravel.log', #存储文件
       $app->make('config')->get('app.log_level', 'debug') #存储级别
     );
}

public function useFiles($path, $level = 'debug') #单一文件
public function useDailyFiles($path, $days = 0, $level = 'debug') #每日生成
public function useSyslog($name = 'laravel', $level = 'debug') #系统日志的方式
public function useErrorLog($level = 'debug', $messageType = ErrorLogHandler::OPERATING_SYSTEM) #等同于php的error_log方式

Log::emergency($error);
Log::alert($error);
Log::critical($error);
Log::error($error);
Log::warning($error);
Log::notice($error);
Log::info($error);
Log::debug($error);