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Introduction to YAML

Paula Santamaría on October 19, 2019

The first time I came across YAML was around a year ago when I use it to write OpenAPI definitions to document a RESTful API using Swagger API Docu...

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orenovadia • Oct 20 '19

Thanks for all the tips and tricks. I like using YAML for configurations.

PS: YAML has some default casting one should be aware of:

In [4]: yaml.load('yes') # 'Yes' and 'No' become boolean
Out[4]: True

In [5]: yaml.load('1_000_000')
Out[5]: 1000000

Paula Santamaría • Oct 21 '19 • Edited

Thank you! According to the YAML 1.2 specification document 'yes' and 'no' are no longer interpreted as boolean.

We have removed unique implicit typing rules and have updated these rules to align them with JSON's productions. In this version of YAML, boolean values may be serialized as “true” or “false”;

You can use !!bool to parse them, though.

Darren Burns • Oct 20 '19

Thanks for this! I just got started with GitHub Actions a couple of days ago, and was making a lot of assumptions on what the YAML was representing -- the translations to JSON you've done here are really helpful :)

Paula Santamaría • Oct 21 '19

Thanks Darren, I'm glad I could help! 🙂

Jacksoft CS • Oct 20 '19

I used YAML file to configure Cluster group in the Pipeline during my internship this past Summer. It was a bit challenging since this was the first time using it but definitely easy to work with. Thanks for sharing this great article.

Paula Santamaría • Oct 21 '19

Nice! Was it your first time working with it? And did its readability made it easier to pickup?

Karam • Oct 19 '19 • Edited

I use YAML for my default config files with tools such as ESLint and Stylelint. I find the syntax a lot more intuitive than JSON and I am less likely to make mistakes with it.

Thank you for making this tutorial, Paula.

Paula Santamaría • Oct 20 '19

Nice! Do you mind sharing a bit more about how you use it? Like which language and do you use a parser?
I'm really curious because I love the syntax, but I don't like the idea of including extra dependencies just for that.

Karam • Oct 20 '19

I currently use yaml only when a node js package offers built-in support for it. I stick with json, otherwise. I don't know much about parsers as I've only used babel before and it doesn't support yaml, as far as I know.

Olimpio • Oct 22 '19

I use YAML so often on Jekyll.. and I didn't know I could write multiline strings just by add this |. Amazing. Thanks.

Paula Santamaría • Oct 22 '19

Something I forgot to include about strings is that you can also write multiline strings that you don't want to be interpreted as multiline. For example:

single-line-string: > 
    This
    should
    be
    one
    line

And this is how it'll look like in JSON:

{
    "single-line-string": "This should be one line\n"
}

When using the > character, instead of |, each new line will be interpreted as an empty space.

Paula Santamaría • Oct 22 '19

I'm glad! Thanks for reading :D

Gabriel Santos • Oct 22 '19

Hi, Paula. Great article!
I have one question, in JSON we can easily create a list of objects without “naming” them, like this:
[{“a”: “b”}, {“x”: “y”}]
How we do that in YAML? For example, a list of Authors (I don’t wanna have [{“authors” : {authoObj1}}, {“authors” : {authoObj2}}])

Paula Santamaría • Oct 22 '19 • Edited

Great question!
You can achieve that by entering the hyphen first and then the properties in a new line, like so:

- 
    name: George
    last-name: Orwell
- 
    name: Stephen
    last-name: King

Which will translate to JSON as:

[
    {
        "name": "George",
        "last-name": "Orwell"
    },
    {
        "name": "Stephen",
        "last-name": "King"
    }
]

Also here's a nice online tool I've been using to try the YAML syntax and see its JSON counterpart.

Abir • Oct 22 '19

I used YAML for my uni assignment where we had to build a ci/cd pipeline using Travis CI for a spring boot application. Travis uses a YAML file for configuration and I found it very easy and intuitive to work with.

Paula Santamaría • Oct 22 '19 • Edited

Nice! Every CI pipeline config I've seen so far uses YAML. I believe we'll be seeing more of it in the near future.

Miguel • May 15 '21

Thanks for this helpful article. I'm using it in K8s to setup the values files and sort of understood the basics of YAML - but this was legit lightbulb. I don't know why I didn't consider that it can be translated to JSON! Thanks again

Antonio R. Rodriguez Gramajo • Mar 4

Thanks for all the tips and tricks!!
I discovered Yaml accidentally, I am learning star and I met him, and also with the link to your article and this beautiful community, this is for me a day of pleasant discoveries.

TuWang • Oct 19 '19

I ran into YAML when working with AWS CloudFormation. It beat me up like a drum 😒

Paula Santamaría • Oct 19 '19

Believe me, I know the feeling!😂
One of the things that made me change my mind after reading about it for a bit was that the whole concept behind YAML made me remember how I felt after going from XML to JSON, which was basically "wow, so much less code, I can actually read this!".

nexus5ooo • Oct 23 '19

I use yaml for Puppet and Ansible

Paula Santamaría • Oct 23 '19

I didn't know any of those so I had to do a quick search. Sounds interesting!

Cem Ugur Karacam • Oct 21 '19

I use it since Jekyll themes use it as configuration data(front matter). As you described, at first glance it seemed weird but once you spend some time, you get used to it.

Paula Santamaría • Oct 22 '19

Yes! Once I found out I could use comments and felt confortable enough to structure the info however I liked I realized how easy it was.

AbhishekUnnikrishnan • Oct 21 '19

I've been using YAML for the last 2 years and I've completely ignored learning anything about it. This was a good beginning.

Thanks

Paula Santamaría • Oct 21 '19

Same here 😂. Its focus in readability makes it easy to pickup without actually learning it, but I always felt a bit uncomfortable with it until I wrote this, I also hated having to google specific stuff like "multi-line strings in yaml".

Prashant Shinde • Oct 20 '19

Super

Paula Santamaría • Oct 21 '19

Thanks!

Anthony Lio • Oct 21 '19

Yay thanks for that post, I've been using it slightly but happy to have learned something on it!

Paula Santamaría • Oct 22 '19

Great! I'm glad I could help :)

Mahmoud Ahmed • Oct 19 '19

I start using YAML in docker and from that time I find it so useful and simple it makes me feel I read an article, not a data file.
Thanks Paula for this amazing article.