--- title: YAML tagline: Cheatsheet for daily use date: 2023-05-19 00:00:00 +100 description: > The Cheatsheet discuss YAML Markups for daily use. YAML (short for "YAML Ain't Markup Language") is a human-readable data serialization format. Its simplicity and readability stand out, making it popular for configuration files and data exchange between systems. keywords: > Jekyll, Theme, JekyllOne, Info, Manual, Cheatsheet, Ruby, Gem categories: [ Manual ] tags: [ Cheatsheet, Gem ] image: path: /assets/images/modules/attics/1920x1280/recha-oktaviani.jpg width: 1920 height: 1280 regenerate: false permalink: /pages/public/tools/cheatsheet/yaml/ resources: [ animate, clipboard, rouge ] resource_options: - attic: slides: - url: /assets/images/modules/attics/1920x1280/recha-oktaviani.jpg alt: Photo by Recha Oktaviani on Unsplash badge: type: unsplash author: Recha Oktaviani href: https://unsplash.com/de/@rechaoktaviani --- // Page Initializer // ============================================================================= // Enable the Liquid Preprocessor :page-liquid: // Set (local) page attributes here // ----------------------------------------------------------------------------- // :page--attr: :yaml-multiline: https://yaml-multiline.info/ // Load Liquid procedures // ----------------------------------------------------------------------------- {% capture load_attributes %}themes/{{site.template.name}}/procedures/global/attributes_loader.proc{%endcapture%} // Load page attributes // ----------------------------------------------------------------------------- {% include {{load_attributes}} scope="global" %} // Page content // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Include sub-documents (if any) // ----------------------------------------------------------------------------- [role="dropcap"] The Cheatsheet discuss Yaml Markups for daily use. _YAML_ (short for YAML Ain't Markup Language) is a human-readable data serialization format. Its simplicity and readability stand out, making it popular for configuration files and data exchange between systems. _YAML_ was designed to be easily readable by humans, focusing on simplicity and conciseness. It uses indentation and whitespace to define the data structure, similar to how Python uses indentation. The Markup Language is widely used for *configuration files* in applications, such as specifying settings for software or defining deployment configurations in infrastructure-as-code tools. _YAML_ is used for data exchange between different systems or programming languages. Jekyll is primarily using the language for defining general *datafiles* like the site config `_config.yml` and the *frontmatter* of pages, posts, and other content files. NOTE: The *frontmatter* provides the data to Jekyll on processing and rendering the content of posts and pages. [role="mb-5"] The following examples give a good overview of YAML documents' most common data structures. Many modern applications, like Jekyll, use YAML documents to provide control data. // Include sub-documents (if any) // ----------------------------------------------------------------------------- [role="mt-5"] == Helpful Links The documentation of _YAML_ is a good source of information but is challenging to read. The tools given below can help to write the correct YAML document, or test your own YAML data codes: mdi:link-variant[24px, md-gray mr-2 ml-3] http://www.yaml.org/spec/1.2/spec.html[YAML 1.2 Spec, {browser-window--new}] + mdi:link-variant[24px, md-gray mr-2 ml-3] http://www.yamllint.com/[Online YAML Linter, {browser-window--new}] + mdi:link-variant[24px, md-gray mr-2 ml-3] https://yaml-online-parser.appspot.com/[Online YAML Parser, {browser-window--new}] NOTE: YAML and JSON are related as data serialization formats, with YAML providing a more human-friendly and expressive syntax, while JSON focuses on simplicity and machine readability. They have overlapping use cases but exhibit some differences in syntax, data types, and readability. JavaScript has built-in support for working with JSON data, making it a popular choice for handling data exchange in web applications. [role="mt-5"] == Scalars In _YAML_, a *scalar* is a basic data element representing a *single value*. Scalars can define strings, numbers, booleans, and null values. Here are the different types of YAML scalars: * *Strings* -- *strings* enclosed in *quotes* or double quotes * *Numbers* -- *numeric* values, including integers and floats * *Booleans* -- *boolean* values, either true or false * *Null* -- *empty* values [source, yaml] ---- integer: 1 float: 1.234 string1: 'abc' string2: "abc" string3: abc boolean: false empty: null ---- .JSON data structure [source, json, role="noclip"] ---- { "integer": 1, "float": 1.234, "string1": "abc", "string2": "abc", "string3": "abc", "boolean": false, "empty": null } ---- === Date Strings Date strings are *scalars* of type *string* follow the *ISO 8601 standard* format. The most common representations of *date* in _YAML_ are: * *Date Only* -- `YYYY-MM-DD`, example: 2023-05-23 * *Date and Time* -- `YYYY-MM-DDTHH:MM:SSZ`, example: 2023-05-23T10:30:00Z In the above format, `T` separates the date and time components, `HH` represents hours in 24-hour format, `MM` represents minutes, `SS` represents seconds, and `Z` indicates that the time is in *UTC* (Coordinated Universal Time). TIP: The time component can also include *milliseconds*, such as `HH:MM:SS.sssZ` (triple `s`). _YAML_ also supports alternative formats for date strings, such as: * *Date and Time with Timezone Offset* -- `YYYY-MM-DDTHH:MM:SS±HH:MM`, example: 2023-05-23T10:30:00-04:00. In this format, the timezone offset is represented as `±HH:MM`, indicating the time difference from *UTC*. * *Date and Time without Timezone* -- `YYYY-MM-DDTHH:MM:SS`, example: 2023-05-23T10:30:00 TIP: When *no timezone* is specified, the time is assumed to be in the *local timezone*. [source, yaml] ---- date1: 2015-04-05 date2: 2022-11-03 00:00:00 +100 ---- .JSON data structure [source, json, role="noclip"] ---- { "date1": "2015-04-05T00:00:00.000Z", "date2": "2022-11-03 00:00:00 +100" } ---- === Multiline strings (HereDoc) A *HereDoc* (short for *here document*) is a way to represent *multi-line* strings or blocks of text within YAML documents. It allows you to define a string value that spans *multiple lines* while preserving the line breaks and formatting. _YAML_ indicates a HereDoc using the *pipe* character (`|`) followed by an optional *indentation level*. The HereDoc block starts on the next line and continues until the indentation is reduced to the level of the initial pipe character or until the end of the document. [source, yaml] ---- message: | This is a multi-line string using a HereDoc. It preserves line breaks and formatting. ---- In this example, the message field contains a multi-line string defined using a HereDoc. The pipe `|` character indicates the start of the HereDoc, and the following lines are indented with two spaces. The resulting value of the message field will include the line breaks and indentation specified within the HereDoc block. [source, json, role="noclip"] ---- { "message": "This is a multi-line\nstring using a HereDoc.\nIt preserves line breaks and formatting.\n" } ---- You can also control the handling of leading and trailing white space within a HereDoc by using *additional symbols*: * `|+` symbol preserves the line breaks and removes trailing white space. It *trims* any spaces or tabs at the *end* of each line. * `|-` symbol preserves the line breaks and removes any leading white space. It *trims* any spaces or tabs at the *beginning* of each line. Here's an example using the different HereDoc *symbols*: [source, yaml] ---- message1: |- This is a HereDoc with leading and trailing spaces. This line has leading spaces. This line has trailing spaces. message2: |+ This is a HereDoc with trailing spaces trimmed. This line has trailing spaces. This line has leading spaces. ---- .JSON data structure [source, json, role="noclip"] ---- { "message1": "This is a HereDoc with leading and trailing spaces.\n This line has leading spaces.\nThis line has trailing spaces. ", "message2": "This is a HereDoc with trailing spaces trimmed.\nThis line has trailing spaces. \nThis line has leading spaces. \n", } ---- In this example: * *message1* uses `|-` to trim *leading* spaces * *message2* uses `|+` to trim *trailing* spaces TIP: Using HereDocs, you can include long, formatted text blocks in your YAML documents without requiring *manual* line concatenation or escaping characters. There is a good online previewer for the different heredoc modes at link:{yaml-multiline}[YAML Multiline, {browser-window--new}]. [role="mt-5"] == Sequences (Arrays) A sequence is a way to represent a *collection* of items. It allows you to define an *ordered list* of values, similar to an *array* or a list in other programming languages. Sequences in _YAML_ are denoted by a *dash* followed by a *space* (` `), and each item in the sequence is placed on a *new line* and *indented*. === Simple sequence In this example, the sequence is represented by the key *fruits* followed by a colon (`:`). The items in the sequence *apple*, *banana*, and *orange* are indented under the key *fruits* using the dash (`- `) notation. [source, yaml] ---- fruits: - apple - banana - orange ---- or written like so: [source, yaml] ---- fruits: [ apple, banana, orange ] ---- .JSON data structure [source, json, role="noclip"] ---- { "fruits": [ "apple", "banana", "orange" ] } ---- === Sequence of sequences In _YAML_, a sequence of sequences (Array of arrays) refers to a structure where a sequence contains other sequences as its elements. Each item in the outer sequence is itself a sequence. It allows you to create a nested collection within an collection. Here's an example of a YAML sequence of sequences: [source, yaml] ---- list_of_lists: - fruits: [ apple, banana, orange ] - colors: [ red, blue, green ] ---- .JSON data structure [source, json, role="noclip"] ---- { "list_of_lists": [ { "fruits": [ "apple", "banana", "orange" ] }, { "colors": [ "red", "blue", "green" ] } ] } ---- You can nest sequences of sequences to represent more complex structures or hierarchical data. Nesting sequences allow you to organize and represent data in a structured manner within YAML documents. [role="mt-5"] == Hash (Dictionary) A hash is a data structure used to represent *key-value pairs*. It is also known as a mapping or *dictionary* in other programming languages. Hashes in YAML are denoted using indentation and a colon to separate the *key* and *value*. === Simple hash [source, yaml] ---- name: John Doe age: 30 email: johndoe@example.com ---- The hash represents a collection of related *key-value pairs*. In the example, *name*, *age*, and *email* are `keys`, and *John Doe+, *30*, and *johndoe@example.com* are their corresponding `values`. .JSON data structure [source, json, role="noclip"] ---- { "name": "John Doe", "age": 30, "email": "johndoe@example.com" } ---- === Named hash [source, yaml] ---- person: name: John Doe age: 30 email: johndoe@example.com ---- .JSON data structure [source, json, role="noclip"] ---- { "person": { "name": "John Doe", "age": 30, "email": "johndoe@example.com" } } ---- === Nested hash Hashes can also be *nested* within other hashes (Hash of Hashes), allowing for more *complex* data structures. Here's an example of a nested hash in _YAML_. [source, yaml] ---- nested_hash: hash1: subsubkey1: 5 subsubkey2: 6 hash2: somethingelse: Important! ---- .JSON data structure [source, json, role="noclip"] ---- { "nested_hash": { "hash1": { "subsubkey1": 5, "subsubkey2": 6 }, "hash2": { "somethingelse": "Important!" } } } ---- [NOTE] ==== Hashes with *JSON* syntax (mixing is possible) [source, yaml] ---- my_hash: { nr1: 5, nr2: 6 } ---- .JSON data structure [source, json, role="noclip"] ---- { "my_hash": { "nr1": 5, "nr2": 6 } } ---- ==== [role="mt-5"] == Content References (Aliases) In _YAML_, content references are a feature that allows you to reference and *reuse* data from one part of a YAML document in another part. They are indicated by an ampersand (`&`) followed by an identifier, and then the *same* identifier preceded by an asterisk (`*`) where the referenced content is to be used. TIP: Content references in _YAML_ provide a way to avoid *duplicating data* and promote reusability. They are particularly useful when you have complex data structures and want to refer to them multiple times within the *same* document. [source, yaml] ---- default_settings: &default_settings install: dir: /usr/local owner: root config: enabled: false run: enabled: true my_app_settings: <<: *default_settings install: owner: my_user group: my_group ---- .JSON data structure [source, json, role="noclip"] ---- { "default_settings": { "install": { "dir": "/usr/local", "owner": "root" }, "config": { "enabled": false }, "run": { "enabled": true } }, "my_app_settings": { "install": { "owner": "my_user", "group": "my_group" }, "config": { "enabled": false }, "run": { "enabled": true } } } ----