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  4. Environment Variable Processors

Environment Variable Processors

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Environment Variable Processors

Using env vars to configure Symfony applications is a common practice to make your applications truly dynamic.

The main issue of env vars is that their values can only be strings and your application may need other data types (integer, boolean, etc.). Symfony solves this problem with “env var processors”, which transform the original contents of the given environment variables. The following example uses the integer processor to turn the value of the HTTP_PORT env var into an integer:

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    # config/packages/framework.yaml
framework:
    router:
        http_port: '%env(int:HTTP_PORT)%'
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    <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config>
        <framework:router http-port="%env(int:HTTP_PORT)%"/>
    </framework:config>
</container>
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    // config/packages/framework.php
$container->loadFromExtension('framework', [
    'router' => [
        'http_port' => '%env(int:HTTP_PORT)%',
    ],
]);

Built-In Environment Variable Processors

Symfony provides the following env var processors:

env(string:FOO)

Casts FOO to a string:

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    # config/packages/framework.yaml
parameters:
    env(SECRET): 'some_secret'
framework:
    secret: '%env(string:SECRET)%'
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    <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(SECRET)">some_secret</parameter>
    </parameters>

    <framework:config secret="%env(string:SECRET)%"/>
</container>
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    // config/packages/framework.php
$container->setParameter('env(SECRET)', 'some_secret');
$container->loadFromExtension('framework', [
    'secret' => '%env(string:SECRET)%',
]);
env(bool:FOO)

Casts FOO to a bool (true values are 'true', 'on', 'yes' and all numbers except 0 and 0.0; everything else is false):

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    # config/packages/framework.yaml
parameters:
    env(HTTP_METHOD_OVERRIDE): 'true'
framework:
    http_method_override: '%env(bool:HTTP_METHOD_OVERRIDE)%'
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    <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(HTTP_METHOD_OVERRIDE)">true</parameter>
    </parameters>

    <framework:config http-method-override="%env(bool:HTTP_METHOD_OVERRIDE)%"/>
</container>
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    // config/packages/framework.php
$container->setParameter('env(HTTP_METHOD_OVERRIDE)', 'true');
$container->loadFromExtension('framework', [
    'http_method_override' => '%env(bool:HTTP_METHOD_OVERRIDE)%',
]);
env(int:FOO)
Casts FOO to an int.
env(float:FOO)
Casts FOO to a float.
env(const:FOO)

Finds the const value named in FOO:

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    # config/packages/security.yaml
parameters:
    env(HEALTH_CHECK_METHOD): 'Symfony\Component\HttpFoundation\Request::METHOD_HEAD'
security:
    access_control:
        - { path: '^/health-check$', methods: '%env(const:HEALTH_CHECK_METHOD)%' }
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    <!-- config/packages/security.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:security="http://symfony.com/schema/dic/security"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/security
        https://symfony.com/schema/dic/security/security-1.0.xsd">

    <parameters>
        <parameter key="env(HEALTH_CHECK_METHOD)">Symfony\Component\HttpFoundation\Request::METHOD_HEAD</parameter>
    </parameters>

    <security:config>
        <rule path="^/health-check$" methods="%env(const:HEALTH_CHECK_METHOD)%"/>
    </security:config>
</container>
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    // config/packages/security.php
$container->setParameter('env(HEALTH_CHECK_METHOD)', 'Symfony\Component\HttpFoundation\Request::METHOD_HEAD');
$container->loadFromExtension('security', [
    'access_control' => [
        [
            'path' => '^/health-check$',
            'methods' => '%env(const:HEALTH_CHECK_METHOD)%',
        ],
    ],
]);
env(base64:FOO)
Decodes the content of FOO, which is a base64 encoded string.
env(json:FOO)

Decodes the content of FOO, which is a JSON encoded string. It returns either an array or null:

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    # config/packages/framework.yaml
parameters:
    env(TRUSTED_HOSTS): '["10.0.0.1", "10.0.0.2"]'
framework:
    trusted_hosts: '%env(json:TRUSTED_HOSTS)%'
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    <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(TRUSTED_HOSTS)">["10.0.0.1", "10.0.0.2"]</parameter>
    </parameters>

    <framework:config trusted-hosts="%env(json:TRUSTED_HOSTS)%"/>
</container>
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    // config/packages/framework.php
$container->setParameter('env(TRUSTED_HOSTS)', '["10.0.0.1", "10.0.0.2"]');
$container->loadFromExtension('framework', [
    'trusted_hosts' => '%env(json:TRUSTED_HOSTS)%',
]);
env(resolve:FOO)

If the content of FOO includes container parameters (with the syntax %parameter_name%), it replaces the parameters by their values:

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    # config/packages/sentry.yaml
parameters:
    env(HOST): '10.0.0.1'
    sentry_host: '%env(HOST)%'
    env(SENTRY_DSN): 'http://%sentry_host%/project'
sentry:
    dsn: '%env(resolve:SENTRY_DSN)%'
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    <!-- config/packages/sentry.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <parameters>
        <parameter key="env(HOST)">10.0.0.1</parameter>
        <parameter key="sentry_host">%env(HOST)%</parameter>
        <parameter key="env(SENTRY_DSN)">http://%sentry_host%/project</parameter>
    </parameters>

    <sentry:config dsn="%env(resolve:SENTRY_DSN)%"/>
</container>
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    // config/packages/sentry.php
$container->setParameter('env(HOST)', '10.0.0.1');
$container->setParameter('sentry_host', '%env(HOST)%');
$container->setParameter('env(SENTRY_DSN)', 'http://%sentry_host%/project');
$container->loadFromExtension('sentry', [
    'dsn' => '%env(resolve:SENTRY_DSN)%',
]);
env(csv:FOO)

Decodes the content of FOO, which is a CSV-encoded string:

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    # config/packages/framework.yaml
parameters:
    env(TRUSTED_HOSTS): "10.0.0.1, 10.0.0.2"
framework:
   trusted_hosts: '%env(csv:TRUSTED_HOSTS)%'
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    <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(TRUSTED_HOSTS)">["10.0.0.1", "10.0.0.2"]</parameter>
    </parameters>

    <framework:config trusted-hosts="%env(csv:TRUSTED_HOSTS)%"/>
</container>
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    // config/packages/framework.php
$container->setParameter('env(TRUSTED_HOSTS)', '["10.0.0.1", "10.0.0.2"]');
$container->loadFromExtension('framework', [
    'trusted_hosts' => '%env(csv:TRUSTED_HOSTS)%',
]);
env(file:FOO)

Returns the contents of a file whose path is the value of the FOO env var:

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    # config/packages/framework.yaml
parameters:
    env(AUTH_FILE): '../config/auth.json'
google:
    auth: '%env(file:AUTH_FILE)%'
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    <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(AUTH_FILE)">../config/auth.json</parameter>
    </parameters>

    <google auth="%env(file:AUTH_FILE)%"/>
</container>
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    // config/packages/framework.php
$container->setParameter('env(AUTH_FILE)', '../config/auth.json');
$container->loadFromExtension('google', [
    'auth' => '%env(file:AUTH_FILE)%',
]);
env(require:FOO)

require() the PHP file whose path is the value of the FOO env var and return the value returned from it.

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    # config/packages/framework.yaml
parameters:
    env(PHP_FILE): '../config/.runtime-evaluated.php'
app:
    auth: '%env(require:PHP_FILE)%'
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    <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(PHP_FILE)">../config/.runtime-evaluated.php</parameter>
    </parameters>

    <app auth="%env(require:PHP_FILE)%"/>
</container>
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    // config/packages/framework.php
$container->setParameter('env(PHP_FILE)', '../config/.runtime-evaluated.php');
$container->loadFromExtension('app', [
    'auth' => '%env(require:PHP_FILE)%',
]);
env(trim:FOO)

Trims the content of FOO env var, removing whitespaces from the beginning and end of the string. This is especially useful in combination with the file processor, as it’ll remove newlines at the end of a file.

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    # config/packages/framework.yaml
parameters:
    env(AUTH_FILE): '../config/auth.json'
google:
    auth: '%env(trim:file:AUTH_FILE)%'
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    <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(AUTH_FILE)">../config/auth.json</parameter>
    </parameters>

    <google auth="%env(trim:file:AUTH_FILE)%"/>
</container>
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    // config/packages/framework.php
$container->setParameter('env(AUTH_FILE)', '../config/auth.json');
$container->loadFromExtension('google', [
    'auth' => '%env(trim:file:AUTH_FILE)%',
]);
env(key:FOO:BAR)

Retrieves the value associated with the key FOO from the array whose contents are stored in the BAR env var:

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    # config/services.yaml
parameters:
    env(SECRETS_FILE): '/opt/application/.secrets.json'
    database_password: '%env(key:database_password:json:file:SECRETS_FILE)%'
    # if SECRETS_FILE contents are: {"database_password": "secret"} it returns "secret"
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    <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(SECRETS_FILE)">/opt/application/.secrets.json</parameter>
        <parameter key="database_password">%env(key:database_password:json:file:SECRETS_FILE)%</parameter>
    </parameters>
</container>
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    // config/services.php
$container->setParameter('env(SECRETS_FILE)', '/opt/application/.secrets.json');
$container->setParameter('database_password', '%env(key:database_password:json:file:SECRETS_FILE)%');
env(default:fallback_param:BAR)

Retrieves the value of the parameter fallback_param when the BAR env var is not available:

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    # config/services.yaml
parameters:
    # if PRIVATE_KEY is not a valid file path, the content of raw_key is returned
    private_key: '%env(default:raw_key:file:PRIVATE_KEY)%'
    raw_key: '%env(PRIVATE_KEY)%'
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    <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">
    <parameters>
        <!-- if PRIVATE_KEY is not a valid file path, the content of raw_key is returned -->
        <parameter key="private_key">%env(default:raw_key:file:PRIVATE_KEY)%</parameter>
        <parameter key="raw_key">%env(PRIVATE_KEY)%</parameter>
    </parameters>
</container>
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    // config/services.php

// if PRIVATE_KEY is not a valid file path, the content of raw_key is returned
$container->setParameter('private_key', '%env(default:raw_key:file:PRIVATE_KEY)%');
$container->setParameter('raw_key', '%env(PRIVATE_KEY)%');

When the fallback parameter is omitted (e.g. env(default::API_KEY)), the value returned is null.

env(url:FOO)

Parses an absolute URL and returns its components as an associative array.

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# .env
MONGODB_URL="mongodb://db_user:[email protected]:27017/db_name"
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    # config/packages/mongodb.yaml
mongo_db_bundle:
    clients:
        default:
            hosts:
                - { host: '%env(key:host:url:MONGODB_URL)%', port: '%env(key:port:url:MONGODB_URL)%' }
            username: '%env(key:user:url:MONGODB_URL)%'
            password: '%env(key:pass:url:MONGODB_URL)%'
    connections:
        default:
            database_name: '%env(key:path:url:MONGODB_URL)%'
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    <!-- config/packages/mongodb.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <mongodb:config>
        <mongodb:client name="default" username="%env(key:user:url:MONGODB_URL)%" password="%env(key:pass:url:MONGODB_URL)%">
            <mongodb:host host="%env(key:host:url:MONGODB_URL)%" port="%env(key:port:url:MONGODB_URL)%"/>
        </mongodb:client>
        <mongodb:connections name="default" database_name="%env(key:path:url:MONGODB_URL)%"/>
    </mongodb:config>
</container>
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    // config/packages/mongodb.php
$container->loadFromExtension('mongodb', [
    'clients' => [
        'default' => [
            'hosts' => [
                [
                    'host' => '%env(key:host:url:MONGODB_URL)%',
                    'port' => '%env(key:port:url:MONGODB_URL)%',
                ],
            ],
            'username' => '%env(key:user:url:MONGODB_URL)%',
            'password' => '%env(key:pass:url:MONGODB_URL)%',
        ],
    ],
    'connections' => [
        'default' => [
            'database_name' => '%env(key:path:url:MONGODB_URL)%',
        ],
    ],
]);

Caution

In order to ease extraction of the resource from the URL, the leading / is trimmed from the path component.

env(query_string:FOO)

Parses the query string part of the given URL and returns its components as an associative array.

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# .env
MONGODB_URL="mongodb://db_user:[email protected]:27017/db_name?timeout=3000"
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    # config/packages/mongodb.yaml
mongo_db_bundle:
    clients:
        default:
            # ...
            connectTimeoutMS: '%env(int:key:timeout:query_string:MONGODB_URL)%'
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    <!-- config/packages/mongodb.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <mongodb:config>
        <mongodb:client name="default" connectTimeoutMS="%env(int:key:timeout:query_string:MONGODB_URL)%"/>
    </mongodb:config>
</container>
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    // config/packages/mongodb.php
$container->loadFromExtension('mongodb', [
    'clients' => [
        'default' => [
            // ...
            'connectTimeoutMS' => '%env(int:key:timeout:query_string:MONGODB_URL)%',
        ],
    ],
]);

It is also possible to combine any number of processors:

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    # config/packages/framework.yaml
parameters:
    env(AUTH_FILE): "%kernel.project_dir%/config/auth.json"
google:
    # 1. gets the value of the AUTH_FILE env var
    # 2. replaces the values of any config param to get the config path
    # 3. gets the content of the file stored in that path
    # 4. JSON-decodes the content of the file and returns it
    auth: '%env(json:file:resolve:AUTH_FILE)%'
  • XML
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    <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(AUTH_FILE)">%kernel.project_dir%/config/auth.json</parameter>
    </parameters>

    <!-- 1. gets the value of the AUTH_FILE env var -->
    <!-- 2. replaces the values of any config param to get the config path -->
    <!-- 3. gets the content of the file stored in that path -->
    <!-- 4. JSON-decodes the content of the file and returns it -->
    <google auth="%env(json:file:resolve:AUTH_FILE)%"/>
</container>
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    // config/packages/framework.php
$container->setParameter('env(AUTH_FILE)', '%kernel.project_dir%/config/auth.json');
// 1. gets the value of the AUTH_FILE env var
// 2. replaces the values of any config param to get the config path
// 3. gets the content of the file stored in that path
// 4. JSON-decodes the content of the file and returns it
$container->loadFromExtension('google', [
    'auth' => '%env(json:file:resolve:AUTH_FILE)%',
]);

Custom Environment Variable Processors

It’s also possible to add your own processors for environment variables. First, create a class that implements Symfony\Component\DependencyInjection\EnvVarProcessorInterface:

use Symfony\Component\DependencyInjection\EnvVarProcessorInterface;

class LowercasingEnvVarProcessor implements EnvVarProcessorInterface
{
    public function getEnv(string $prefix, string $name, \Closure $getEnv)
    {
        $env = $getEnv($name);

        return strtolower($env);
    }

    public static function getProvidedTypes()
    {
        return [
            'lowercase' => 'string',
        ];
    }
}

To enable the new processor in the app, register it as a service and tag it with the container.env_var_processor tag. If you’re using the default services.yaml configuration, this is already done for you, thanks to autoconfiguration.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.