3,169 bytes added
, 11 April
[[File:Jinja-logo-sidebar.png|right]]
For background perspective, '''[https://jinja.palletsprojects.com Jinja]''' is used as a templating system by various Python projects like Django, Flask, or Ansible.
From the Jinja2 documentation, there are two options to control whitespace in Jinja templates:
* <code>trim_blocks</code>
* <code>lstrip_blocks</code>
But actually, there's more to it. [https://jinja.palletsprojects.com/en/3.1.x/templates/ The "Template Designer Documentation"] specifically for [https://jinja.palletsprojects.com/en/3.1.x/templates/#whitespace-control whitespace control] is inadequate. That's why I wrote this article.
== Jinja in Ansible ==
In [[Ansible]]'s Template module, you can see in the source code
* [https://github.com/search?q=repo%3Aansible%2Fansible%20trim_blocks&type=code trim_blocks defaults to true]
* [https://github.com/search?q=repo%3Aansible%2Fansible%20lstrip_blocks&type=code lstrip_blocks defaults to false]
But what does this mean? What do these options do? And how do I use them in my Ansible templates?
'''trim blocks''' means the first newline after a block is removed (block, not variable tag!)
'''lstrip blocks''' <ref><code>lstrip</code> stands for "left strip". It is a function in Python, as well as R and Ruby. Like <code>ltrim</code> in PHP or <code>trimStart</code> in JavaScript. nb. Jinja also has a [https://jinja.palletsprojects.com/en/3.1.x/templates/#list-of-builtin-filters built-in filter] named <code>[https://jinja.palletsprojects.com/en/3.1.x/templates/#jinja-filters.trim trim]</code> that is used to strip characters from the beginning and end of a string.</ref> means leading spaces and tabs are stripped from the start of a line to a block.
So, I can read words, but without context nor further example and explanation, I can't decode what "from the start of a line to a block" means.
== In the task ==
In at least v2.9 of Ansible, the Template module has options to specify both.
* [https://docs.ansible.com/ansible/2.9/modules/template_module.html 2.9 docs for the template module] []
* [https://docs.ansible.com/ansible/latest/modules/template_module.html latest docs for the template module]
** [https://docs.ansible.com/ansible/latest/collections/ansible/builtin/template_module.html#parameter-lstrip_blocks parameter lstrip_blocks]
** [https://docs.ansible.com/ansible/latest/collections/ansible/builtin/template_module.html#parameter-trim_blocks parameter trim_blocks]
== In the template file ==
As the '''very first line''' of your template file, you can use a magic comment directive to control the behavior of the Ansible Template module
<code>#jinja2: trim_blocks: "true", lstrip_blocks: "true"</code><ref>It's unclear whether the boolean value(s) to be quoted. I believe it was a bug that is now fixed - meaning they can be bare.</ref>
== By hand ==
If you're confused about Variable notation and how those are defined in templates, see https://jinja.palletsprojects.com/en/3.1.x/templates/#variables
== Debugging ==
Just put <code>{% debug %}</code> somewhere in your template file.
{{References}}
[[Category:Ansible]]
[[Category:Templating]]
[[Category:Python]]