added docs for the env component

Author: fabpot

components/dotenv.rst

@@ -0,0 +1,113 @@
+.. index::
+   single: Dotenv
+   single: Components; Dotenv
+
+The Dotenv Component
+====================
+
+    The Dotenv Component parses ``.env`` files to make environment variables
+    stored in them accessible via ``getenv()``, ``$_ENV`` or ``$_SERVER``.
+
+Installation
+------------
+
+You can install the component in 2 different ways:
+
+* :doc:`Install it via Composer </components/using_components>` (``symfony/dotenv`` on `Packagist`_);
+* Use the official Git repository (https://github.com/symfony/dotenv).
+
+.. include:: /components/require_autoload.rst.inc
+
+Usage
+-----
+
+Sensitive information and environment-dependent settings should be defined as
+environment variables (as recommended for `twelve-factor applications`_. Using
+an ``.env`` file to store those environment variables eases development and CI
+management by keeping them in one "standard" place and agnostic of the
+technology stack you are using (Nginx vs PHP built-in server for instance).
+
+.. note::
+
+    PHP has a lot of different implementations of this "pattern". This
+    implementation's goal is to replicate what ``source .env`` would do. So, it
+    tries to be as similar as possible with the default shell's behavior, and
+    does not do anything not possible via ``source`` (like value validation).
+
+Usage
+-----
+
+First, require Symfony Dotenv via Composer:
+
+.. code-block:: bash
+
+    composer require symfony/dotenv
+
+Load an ``.env`` file in your PHP application via ``Dotenv::load()``::
+
+    use Symfony\Component\Dotenv\Dotenv;
+
+    $dotenv = new Dotenv();
+    $dotenv->load(__DIR__.'/.env');
+
+    // You can also load several files
+    $dotenv->load(__DIR__.'/.env', __DIR__.'/.env.dev');
+
+Given the following ``.env`` file content:
+
+.. code-block:: bash
+
+    # .env
+    DB_USER=root
+    DB_PASS=pass
+
+Access the value with ``getenv()`` in your code::
+
+    $dbUser = getenv('DB_USER');
+    // you can also use ``$_ENV`` or ``$_SERVER``
+
+.. note::
+
+    Symfony Env never overwrites existing environment variables.
+
+You should never store a ``.env`` file in your code repository as it might
+contain sensitive information; create a ``.env.dist`` file with sensible
+defaults instead.
+
+Symfony Env should only be used in development/testing/staging environments.
+For production environments, use "real" environment variables.
+
+As a ``.env`` file is a regular shell script, you can ``source`` it in your own
+shell scripts:
+
+.. code-block:: bash
+
+    source .env
+
+Add comments by prefixing them with ``#``:
+
+.. code-block:: bash
+
+    # Database credentials
+    DB_USER=root
+    DB_PASS=pass # This is the secret password
+
+Use environment variables in values by prefixing variables with ``$``:
+
+.. code-block:: bash
+
+    DB_USER=root
+    DB_PASS=${DB_USER}pass # Include the user as a password prefix
+
+Embed commands via ``$()`` (not supported on Windows):
+
+.. code-block:: bash
+
+    START_TIME=$(date)
+
+.. note::
+
+    Note that using ``$()`` might not work depending on your shell.
+
+.. _Packagist: https://packagist.org/packages/symfony/dotenv
+.. _twelve-factor applications: http://www.12factor.net/