.. _playbooks_advanced_syntax:

************************
Advanced playbook syntax
************************

The advanced YAML syntax examples on this page give you more control over the data placed in YAML files used by Ansible.
You can find additional information about Python-specific YAML in the official `PyYAML Documentation <https://pyyaml.org/wiki/PyYAMLDocumentation#YAMLtagsandPythontypes>`_.

.. _unsafe_strings:

Unsafe or raw strings
=====================

When handling values returned by lookup plugins, Ansible uses a data type called ``unsafe`` to block templating. Marking data as unsafe prevents malicious users from abusing Jinja2 templates to execute arbitrary code on target machines. The Ansible implementation ensures that unsafe values are never templated. It is more comprehensive than escaping Jinja2 with ``{% raw %} ... {% endraw %}`` tags.

You can use the same ``unsafe`` data type in variables you define, to prevent templating errors and information disclosure. You can mark values supplied by :ref:`vars_prompts<unsafe_prompts>` as unsafe. You can also use ``unsafe`` in playbooks. The most common use cases include passwords that allow special characters like ``{`` or ``%``, and JSON arguments that look like templates but should not be templated. For example:

.. code-block:: yaml

    ---
    mypassword: !unsafe 234%234{435lkj{{lkjsdf

In a playbook:

.. code-block:: yaml

    ---
    hosts: all
    vars:
      my_unsafe_variable: !unsafe 'unsafe % value'
    tasks:
        ...

For complex variables such as hashes or arrays, use ``!unsafe`` on the individual elements:

.. code-block:: yaml

    ---
    my_unsafe_array:
      - !unsafe 'unsafe element'
      - 'safe element'

    my_unsafe_hash:
      unsafe_key: !unsafe 'unsafe value'

.. _anchors_and_aliases:

YAML anchors and aliases: sharing variable values
=================================================

`YAML anchors and aliases <https://yaml.org/spec/1.2/spec.html#id2765878>`_ help you define, maintain, and flexibly use shared variable values.
You define an anchor with ``&``, then refer to it using an alias, denoted with ``*``. Here's an example that sets three values with an anchor, uses two of those values with an alias, and overrides the third value:

.. code-block:: yaml

    ---
    # ...
    vars:
      app1:
        jvm: &jvm_opts
          opts: '-Xms1G -Xmx2G'
          port: 1000
          path: /usr/lib/app1
      app2:
        jvm:
          <<: *jvm_opts
          path: /usr/lib/app2
    # ...

Here, ``app1`` and ``app2`` share the values for ``opts`` and ``port`` using the anchor ``&jvm_opts`` and the alias ``*jvm_opts``.
The value for ``path`` is merged by ``<<`` or `merge operator <https://yaml.org/type/merge.html>`_.

Anchors and aliases also let you share complex sets of variable values, including nested variables. If you have one variable value that includes another variable value, you can define them separately:

.. code-block:: yaml

      vars:
        webapp_version: 1.0
        webapp_custom_name: ToDo_App-1.0

This is inefficient and, at scale, means more maintenance. To incorporate the version value in the name, you can use an anchor in ``app_version`` and an alias in ``custom_name``:

.. code-block:: yaml

      vars:
        webapp:
            version: &my_version 1.0
            custom_name:
                - "ToDo_App"
                - *my_version

Now, you can reuse the value of ``app_version`` within the value of  ``custom_name`` and use the output in a template:

.. code-block:: yaml

    ---
    - name: Using values nested inside dictionary
      hosts: localhost
      vars:
        webapp:
          version: &my_version 1.0
          custom_name:
            - "ToDo_App"
            - *my_version
      tasks:
      - name: Using Anchor value
        ansible.builtin.debug:
          msg: My app is called "{{ webapp.custom_name | join('-') }}".

You've anchored the value of ``version`` with the ``&my_version`` anchor and reused it with the ``*my_version`` alias. Anchors and aliases let you access nested values inside dictionaries.

.. seealso::

   :ref:`playbooks_variables`
       All about variables
   :ref:`complex_data_manipulation`
       Doing complex data manipulation in Ansible
   :ref:`Communication<communication>`
       Got questions? Need help? Want to share your ideas? Visit the Ansible communication guide
