168 lines
5.2 KiB
ReStructuredText
168 lines
5.2 KiB
ReStructuredText
YAML Syntax
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===========
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This page provides a basic overview of correct YAML syntax, which is how Ansible
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playbooks (our configuration management language) are expressed.
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We use YAML because it is easier for humans to read and write than other common
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data formats like XML or JSON. Further, there are libraries available in most
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programming languages for working with YAML.
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You may also wish to read :doc:`playbooks` at the same time to see how this
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is used in practice.
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YAML Basics
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-----------
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For Ansible, nearly every YAML file starts with a list.
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Each item in the list is a list of key/value pairs, commonly
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called a "hash" or a "dictionary". So, we need to know how
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to write lists and dictionaries in YAML.
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There's another small quirk to YAML. All YAML files (regardless of their association with Ansible or not) can optionally
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begin with ``---`` and end with ``...``. This is part of the YAML format and indicates the start and end of a document.
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All members of a list are lines beginning at the same indentation level starting with a ``"- "`` (a dash and a space)::
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---
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# A list of tasty fruits
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fruits:
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- Apple
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- Orange
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- Strawberry
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- Mango
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...
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A dictionary is represented in a simple ``key: value`` form (the colon must be followed by a space)::
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# An employee record
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martin:
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name: Martin D'vloper
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job: Developer
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skill: Elite
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More complicated data structures are possible, such as lists of dictionaries, dictionaries whose values are lists or a mix of both::
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# Employee records
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- martin:
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name: Martin D'vloper
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job: Developer
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skills:
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- python
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- perl
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- pascal
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- tabitha:
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name: Tabitha Bitumen
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job: Developer
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skills:
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- lisp
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- fortran
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- erlang
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Dictionaries and lists can also be represented in an abbreviated form if you really want to::
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---
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martin: {name: Martin D'vloper, job: Developer, skill: Elite}
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fruits: ['Apple', 'Orange', 'Strawberry', 'Mango']
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.. _truthiness:
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Ansible doesn't really use these too much, but you can also specify a boolean value (true/false) in several forms::
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create_key: yes
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needs_agent: no
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knows_oop: True
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likes_emacs: TRUE
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uses_cvs: false
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Values can span multiple lines using ``|`` or ``>``. Spanning multiple lines using a ``|`` will include the newlines. Using a ``>`` will ignore newlines; it's used to make what would otherwise be a very long line easier to read and edit.
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In either case the indentation will be ignored.
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Examples are::
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include_newlines: |
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exactly as you see
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will appear these three
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lines of poetry
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ignore_newlines: >
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this is really a
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single line of text
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despite appearances
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Let's combine what we learned so far in an arbitrary YAML example.
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This really has nothing to do with Ansible, but will give you a feel for the format::
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---
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# An employee record
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name: Martin D'vloper
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job: Developer
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skill: Elite
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employed: True
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foods:
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- Apple
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- Orange
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- Strawberry
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- Mango
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languages:
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perl: Elite
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python: Elite
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pascal: Lame
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education: |
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4 GCSEs
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3 A-Levels
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BSc in the Internet of Things
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That's all you really need to know about YAML to start writing `Ansible` playbooks.
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Gotchas
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-------
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While YAML is generally friendly, the following is going to result in a YAML syntax error::
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foo: somebody said I should put a colon here: so I did
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You will want to quote any hash values using colons, like so::
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foo: "somebody said I should put a colon here: so I did"
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And then the colon will be preserved.
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Further, Ansible uses "{{ var }}" for variables. If a value after a colon starts
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with a "{", YAML will think it is a dictionary, so you must quote it, like so::
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foo: "{{ variable }}"
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The same applies for strings that start or contain any YAML special characters ``[] {} : > |`` .
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Boolean conversion is helpful, but this can be a problem when you want a literal `yes` or other boolean values as a string.
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In these cases just use quotes::
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non_boolean: "yes"
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other_string: "False"
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YAML converts certain strings into floating-point values, such as the string
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`1.0`. If you need to specify a version number (in a requirements.yml file, for
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example), you will need to quote the value if it looks like a floating-point
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value::
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version: "1.0"
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.. seealso::
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:doc:`playbooks`
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Learn what playbooks can do and how to write/run them.
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`YAMLLint <http://yamllint.com/>`_
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YAML Lint (online) helps you debug YAML syntax if you are having problems
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`Github examples directory <https://github.com/ansible/ansible-examples>`_
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Complete playbook files from the github project source
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`Wikipedia YAML syntax reference <https://en.wikipedia.org/wiki/YAML>`_
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A good guide to YAML syntax
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`Mailing List <http://groups.google.com/group/ansible-project>`_
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Questions? Help? Ideas? Stop by the list on Google Groups
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`irc.freenode.net <http://irc.freenode.net>`_
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#ansible IRC chat channel
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