How can I include a YAML file inside another?

In YAML, you can merge multiple files or sections using the special << operator and * reference. This method is commonly referred to as 'anchors' and 'aliases'. However, note that standard YAML does not directly support loading one file into another. Instead, some programs or libraries that handle YAML support custom extensions to achieve this functionality.

I will walk you through the process step by step if your environment supports such extensions for including a YAML file within another file. For example, popular programming language libraries such as Python's PyYAML allow you to include other files using specific markers within YAML files.

Example

Assume we have two YAML files: common.yml containing some common configuration, and config.yml that needs to include the content of common.yml.

common.yml:

yaml
default_settings:
  setting1: value1
  setting2: value2

config.yml:

yaml
include common.yml

specific_settings:
  setting3: value3

In the above example, include common.yml is an illustrative marker; the actual implementation depends on the library or tool you are using.

Implementation Method

If you use Python with the PyYAML library, you can customize a constructor to handle this inclusion.

python
import yaml

def include(loader, node):
    with open(node.value) as inputfile:
        return yaml.load(inputfile, Loader=yaml.FullLoader)

yaml.add_constructor('!include', include)

with open('config.yml', 'r') as f:
    data = yaml.load(f, Loader=yaml.FullLoader)
    print(data)

In this Python example, we define a function named include that opens the specified file and loads its content into the current YAML structure. We register this function as the processor for the !include marker using yaml.add_constructor.

Modified config.yml:

yaml
default_settings: !include common.yml

specific_settings:
  setting3: value3

With the !include marker, the config.yml file can now include content loaded from common.yml.

Important Notes

• Ensure that your environment or library supports file inclusion operations, or you can customize the implementation.
• Be mindful of security issues, especially when loading YAML files from untrusted sources.

By doing this, you can effectively reuse YAML configurations, making them more modular and easier to manage.