关于Lumen / Laravel .env 文件中的环境变量是如…

　　.env 文件可自定义其他任何有效的环境变量，并可通过  调用 env() 或 $_SERVER 或 $_ENV  来获取该变量。那么env()是如何加载到这些变量的呢？

• 函数env()：在Lumen的vendor/laravel/lumen-framework/src/helpers.php中，我们可以发现env函数是这样被定义的：

  if (! function_exists('env')) {
      /**
       * Gets the value of an environment variable. Supports boolean, empty and null.
       *
       * @param  string  $key
       * @param  mixed   $default
       * @return mixed
       */
      function env($key, $default = null)
      {
          $value = getenv($key);
  
          if ($value === false) {
              return value($default);
          }
  
          switch (strtolower($value)) {
              case 'true':
              case '(true)':
                  return true;
  
              case 'false':
              case '(false)':
                  return false;
  
              case 'empty':
              case '(empty)':
                  return '';
  
              case 'null':
              case '(null)':
                  return;
          }
  
          if (Str::startsWith($value, '"') && Str::endsWith($value, '"')) {
              return substr($value, 1, -1);
          }
  
          return $value;
      }
  }

  可见，env函数中调用了 getenv() 来读取环境变量。

• vlucas/phpdotenv：我们知道getenv()是PHP原生提供可读取   $_SERVER 或 $_ENV   全局变量的函数API，.env文件中的环境变量为何可以通过getenv()来获取呢？vlucas/phpdotenv 就是这个幕后功臣，在Lumen 或 Laravel 的vendor下可以找到她，如果要单独下载她，去这里 ：https://github.com/vlucas/phpdotenv 。在vlucas/phpdotenv/src/Loader.php文件中，我们可以看到.env被加载进一个数组，然后把每一行看作setter并调用setEnvironmentVariable()方法：

  /**
       * Load `.env` file in given directory.
       *
       * @return array
       */
      public function load()
      {
          $this->ensureFileIsReadable();
  
          $filePath = $this->filePath;
          $lines = $this->readLinesFromFile($filePath);
          foreach ($lines as $line) {
              if (!$this->isComment($line) && $this->looksLikeSetter($line)) {
                  $this->setEnvironmentVariable($line);
              }
          }
  
          return $lines;
      }
  
  /**
       * Read lines from the file, auto detecting line endings.
       *
       * @param string $filePath
       *
       * @return array
       */
      protected function readLinesFromFile($filePath)
      {
          // Read file into an array of lines with auto-detected line endings
          $autodetect = ini_get('auto_detect_line_endings');
          ini_set('auto_detect_line_endings', '1');
          $lines = file($filePath, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
          ini_set('auto_detect_line_endings', $autodetect);
  
          return $lines;
      }

  Loader::setEnvironmentVariable($name, $value = null) 的定义如下：

  /**
       * Set an environment variable.
       *
       * This is done using:
       * - putenv,
       * - $_ENV,
       * - $_SERVER.
       *
       * The environment variable value is stripped of single and double quotes.
       *
       * @param string      $name
       * @param string|null $value
       *
       * @return void
       */
      public function setEnvironmentVariable($name, $value = null)
      {
          list($name, $value) = $this->normaliseEnvironmentVariable($name, $value);
  
          // Don't overwrite existing environment variables if we're immutable
          // Ruby's dotenv does this with `ENV[key] ||= value`.
          if ($this->immutable && $this->getEnvironmentVariable($name) !== null) {
              return;
          }
  
          // If PHP is running as an Apache module and an existing
          // Apache environment variable exists, overwrite it
          if (function_exists('apache_getenv') && function_exists('apache_setenv') && apache_getenv($name)) {
              apache_setenv($name, $value);
          }
  
          if (function_exists('putenv')) {
              putenv("$name=$value");
          }
  
          $_ENV[$name] = $value;
          $_SERVER[$name] = $value;
      }

   

• PHP dotenv 是什么：

  Loads environment variables from .env to getenv(), $_ENV and $_SERVER automagically.
  
  This is a PHP version of the original Ruby dotenv.

   

• Why .env：

  You should never store sensitive credentials in your code. Storing configuration in the environment is one of the tenets of a twelve-factor app. Anything that is likely to change between deployment environments – such as database credentials or credentials for 3rd party services – should be extracted from the code into environment variables.
  
  Basically, a .env file is an easy way to load custom configuration variables that your application needs without having to modify .htaccess files or Apache/nginx virtual hosts. This means you won't have to edit any files outside the project, and all the environment variables are always set no matter how you run your project - Apache, Nginx, CLI, and even PHP 5.4's built-in webserver. It's WAY easier than all the other ways you know of to set environment variables, and you're going to love it.
  
  . NO editing virtual hosts in Apache or Nginx
  . NO adding php_value flags to .htaccess files
  . EASY portability and sharing of required ENV values
  . COMPATIBLE with PHP's built-in web server and CLI runner

   

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