Environment Variable Processors

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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)%'

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)%'
env(bool:FOO)

Casts FOO to a bool (true values are 'true', 'on', 'yes', all numbers except 0 and 0.0 and all numeric strings 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)%'
env(not:FOO)

Casts FOO to a bool (just as env(bool:...) does) except it returns the inverted value (falsy values are returned as true, truthy values are returned as false):

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# config/services.yaml
parameters:
    safe_for_production: '%env(not:APP_DEBUG)%'
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)%' }
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(ALLOWED_LANGUAGES): '["en","de","es"]'
    app_allowed_languages: '%env(json:ALLOWED_LANGUAGES)%'
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:
    sentry_host: '10.0.0.1'
    env(SENTRY_DSN): 'http://%sentry_host%/project'
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(ALLOWED_LANGUAGES): "en,de,es"
    app_allowed_languages: '%env(csv:ALLOWED_LANGUAGES)%'
env(shuffle:FOO)

Randomly shuffles values of the FOO env var, which must be an array.

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# config/packages/framework.yaml
parameters:
    env(REDIS_NODES): "127.0.0.1:6380,127.0.0.1:6381"
services:
    RedisCluster:
        class: RedisCluster
        arguments: [null, "%env(shuffle:csv:REDIS_NODES)%"]
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): '%kernel.project_dir%/config/auth.json'
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): '%kernel.project_dir%/config/.runtime-evaluated.php'
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): '%kernel.project_dir%/config/auth.json'
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"
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)%'

When the fallback parameter is omitted (e.g. env(default::API_KEY)), then the returned value 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:db_password@127.0.0.1:27017/db_name"
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# config/packages/mongodb.yaml
mongo_db_bundle:
    clients:
        default:
            hosts:
                - { host: '%env(string:key:host:url:MONGODB_URL)%', port: '%env(int:key:port:url:MONGODB_URL)%' }
            username: '%env(string:key:user:url:MONGODB_URL)%'
            password: '%env(string: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:db_password@127.0.0.1:27017/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)%'
env(enum:FooEnum:BAR)

Tries to convert an environment variable to an actual \BackedEnum value. This processor takes the fully qualified name of the \BackedEnum as an argument:

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// App\Enum\Suit.php
enum Suit: string
{
    case Clubs = 'clubs';
    case Spades = 'spades';
    case Diamonds = 'diamonds';
    case Hearts = 'hearts';
}
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# config/services.yaml
parameters:
    suit: '%env(enum:App\Enum\Suit:CARD_SUIT)%'

The value stored in the CARD_SUIT env var would be a string (e.g. 'spades') but the application will use the enum value (e.g. Suit::Spades).

env(defined:NO_FOO)

Evaluates to true if the env var exists and its value is not '' (an empty string) or null; it returns false otherwise.

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# config/services.yaml
parameters:
    typed_env: '%env(defined:FOO)%'

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)%'

Custom Environment Variable Processors

It's also possible to add your own processors for environment variables. First, create a class that implements EnvVarProcessorInterface:

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use Symfony\Component\DependencyInjection\EnvVarProcessorInterface;

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

        return strtolower($env);
    }

    public static function getProvidedTypes(): array
    {
        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.
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