.env 檔案可自訂其他任何有效的環境變量，並可透過 呼叫env() 或$_SERVER 或$_ENV 來取得該變數。那麼env()是如何載入到這些變數的呢？在Lumen的vendor/laravel/lumen-framework/src/helpers.php中，我們可以發現env函式是這樣被定義的：
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;
}
}可見，env函式中呼叫了getenv () 來讀取環境變數。我們又知道getenv()是PHP原生提供可讀 $_SERVER 或$_ENV 全域變數的函數API，.env檔案中的環境變數為何可以透過getenv()來取得呢？ vlucas/phpdotenv 就是這個幕後功臣，在Lumen 或 Laravel 的vendor下可以找到她，如果要單獨下載她，去這裡 ： 。
在vlucas/phpdotenv/src/Loader.php檔案中，我們可以看到.env被載入進一個數組，然後把每一行看作setter並呼叫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 ) 的定義如下：
/**
* 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 itif (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 她是什麼？
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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