YAML does not come with a standard PHP installation, instead it needs to be installed as a PECL extension. On linux/unix it can be installed with a simple

pecl install yaml

Note that libyaml-dev package must be installed on the system, as the PECL package is simply a wrapper around libYAML calls.

Installation on Windows machines is different - you can either download a pre-compiled DLL or build from sources.

YAML provides a way to store structured data. The data can be a simple set of name-value pairs or a complex hierarchical data with values even being arrays.

Consider the following YAML file:

database:
    driver: mysql
    host: database.mydomain.com
    port: 3306
    db_name: sample_db
    user: myuser
    password: Passw0rd
debug: true
country: us

Let's say, it's saved as config.yaml. Then to read this file in PHP the following code can be used:

$config = yaml_parse_file('config.yaml');
print_r($config);

print_r will produce the following output:

Array
(
    [database] => Array
        (
            [driver] => mysql
            [host] => database.mydomain.com
            [port] => 3306
            [db_name] => sample_db
            [user] => myuser
            [password] => Passw0rd
        )

    [debug] => 1
    [country] => us
)

Now config parameters can be used by simply using array elements:

$dbConfig = $config['database'];

$connectString = $dbConfig['driver']
    . ":host={$dbConfig['host']}"
    . ":port={$dbConfig['port']}"
    . ":dbname={$dbConfig['db_name']}"
    . ":user={$dbConfig['user']}"
    . ":password={$dbConfig['password']}";
$dbConnection = new \PDO($connectString, $dbConfig['user'], $dbConfig['password']);