What is yaml

The basic structure of a YAML file is a map. You might call this a dictionary, hash or object, depending on your programming language or mood. You can use all sorts of scalar types as values: numbers, booleans, and strings quoted or not. The first line of a config. Words in keys can be separated by underscores, dashes, or spaces. At CircleCI, we use underscores.

We saw floating point and integers above. YAML supports several other numeric types. An integer can be decimal, hexidecimal, or octal. As you expect, Ox indicates a value is hex, and a leading zero denotes an octal value. YAML supports both fixed and exponential floating point numbers. YAML processes the first value as ending with a carriage return and linefeed. YAML will not escape strings with single quotes, but the single quotes do avoid having string contents interpreted as document formatting.

String values can span more than one line. With the fold greater than character, you can specify a string in a block. False is indicated with False, Off, or No. We covered dictionaries above, but there's more to them. Like arrays, you can put dictionaries inline. We saw this format above. It's how python prints dictionaries. Multiline values may end with whitespace, and depending on how you want the document to be processed you might not want to preserve it.

YAML has the strip chomp and preserve chomp operators. To save the last character, add a plus to the fold or block operators. So, if the value ends with whitespace, like a newline, YAML will preserve it.

To strip the character, use the strip operator. A document starts with three dashes and ends with three periods. Some YAML processors require the document start operator. The end operator is usually optional. You'll usually use the end document operator when a file contains multiple documents. Let's modify our python code. Now, let's process a compound document with it. YAML is a powerful language that can be used for configuration files, messages between applications, and saving application state.

Like all programming languages , YAML is not without its faults. Because it was designed specifically to be easy to read and write mistakes are far more easier to make than with other languages. This also means that changes can be made to your YAML could by very simple typos, like adding an extra space, which can be more difficult to spot as it is on a sparse, white background.

This choice of tools ranges such as Helm, that streamlines installing and managing Kubernetes apps to managed cloud services, to the kubectl command line. Tools such as Pulumi, that use familiar programming languages like JavaScript or PowerShell, also fall into this camp. Explore why the most efficient way forward is data-driven. Critical vulnerabilities in Philips EMR system could risk patient data. You can think of a sequence as a Python list or an array in Bash or Perl.

A list can be embedded into a map. YAML also contains scalars, which are arbitrary data encoded in Unicode that can be used as values such as strings, integers, dates, numbers, or booleans. A linter is an application that verifies the syntax of a file. Here's an example of a simple YAML file for an employee record that demonstrates the syntax rules. One of the most common uses for YAML is to create configuration files.

YAML is also used by the automation tool Ansible to create automation processes, and for Kubernetes resources and deployments. Ansible Playbooks are used to orchestrate IT processes. A playbook is a YAML file containing 1 or more plays, and is used to define the desired state of a system.

Each play can run one or more tasks, and each task invokes an Ansible module. Modules are used to accomplish automation tasks in Ansible. An Ansible Playbook consists of maps and lists. To create a playbook, start a YAML list that names the play, and then lists tasks in a sequence. Remember that indentation is not an indication of logical inheritance. Think of each line as a YAML data type a list or a map. By using YAML templates, Ansible users can program repetitive tasks to happen automatically without having to learn an advanced programming language.

Kubernetes works based on defined state and actual state. Kubernetes objects represent the state of a cluster and tell Kubernetes what you want the workload to look like.