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7cd43d8ad4
* YAML allows literal tabs in content, but not indentation.
* Two space indent always preferred.
* Note: YAML dumpers always use 2 space by default.
* '- ...' doesn't need extra indentation.
* Note: YAML dumpers don't use extra indentation.
* There was no mention of single quoted strings. They are preferred
and should be used except when double quote semantics are actually
required. (Best practice).
* Add flow form example for sets: `{a, b, c}`
* Show collapsed form of seq-in-seq: `- - - foo`.
179 lines
5.2 KiB
Markdown
179 lines
5.2 KiB
Markdown
---
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language: yaml
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filename: learnyaml.yaml
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contributors:
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- [Adam Brenecki, 'https://github.com/adambrenecki']
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- [Suhas SG, 'https://github.com/jargnar']
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---
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YAML is a data serialisation language designed to be directly writable and
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readable by humans.
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It's a strict superset of JSON, with the addition of syntactically
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significant newlines and indentation, like Python. Unlike Python, however,
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YAML doesn't allow literal tab characters for indentation.
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```yaml
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# Comments in YAML look like this.
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################
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# SCALAR TYPES #
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################
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# Our root object (which continues for the entire document) will be a map,
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# which is equivalent to a dictionary, hash or object in other languages.
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key: value
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another_key: Another value goes here.
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a_number_value: 100
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scientific_notation: 1e+12
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# The number 1 will be interpreted as a number, not a boolean. if you want
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# it to be interpreted as a boolean, use true
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boolean: true
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null_value: null
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key with spaces: value
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# Notice that strings don't need to be quoted. However, they can be.
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however: 'A string, enclosed in quotes.'
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'Keys can be quoted too.': "Useful if you want to put a ':' in your key."
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single quotes: 'have ''one'' escape pattern'
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double quotes: "have many: \", \0, \t, \u263A, \x0d\x0a == \r\n, and more."
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# Multiple-line strings can be written either as a 'literal block' (using |),
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# or a 'folded block' (using '>').
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literal_block: |
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This entire block of text will be the value of the 'literal_block' key,
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with line breaks being preserved.
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The literal continues until de-dented, and the leading indentation is
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stripped.
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Any lines that are 'more-indented' keep the rest of their indentation -
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these lines will be indented by 4 spaces.
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folded_style: >
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This entire block of text will be the value of 'folded_style', but this
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time, all newlines will be replaced with a single space.
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Blank lines, like above, are converted to a newline character.
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'More-indented' lines keep their newlines, too -
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this text will appear over two lines.
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####################
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# COLLECTION TYPES #
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####################
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# Nesting uses indentation. 2 space indent is preferred (but not required).
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a_nested_map:
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key: value
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another_key: Another Value
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another_nested_map:
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hello: hello
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# Maps don't have to have string keys.
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0.25: a float key
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# Keys can also be complex, like multi-line objects
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# We use ? followed by a space to indicate the start of a complex key.
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? |
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This is a key
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that has multiple lines
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: and this is its value
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# YAML also allows mapping between sequences with the complex key syntax
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# Some language parsers might complain
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# An example
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? - Manchester United
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- Real Madrid
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: [ 2001-01-01, 2002-02-02 ]
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# Sequences (equivalent to lists or arrays) look like this
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# (note that the '-' counts as indentation):
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a_sequence:
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- Item 1
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- Item 2
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- 0.5 # sequences can contain disparate types.
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- Item 4
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- key: value
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another_key: another_value
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-
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- This is a sequence
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- inside another sequence
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- - - Nested sequence indicators
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- can be collapsed
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# Since YAML is a superset of JSON, you can also write JSON-style maps and
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# sequences:
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json_map: {"key": "value"}
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json_seq: [3, 2, 1, "takeoff"]
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and quotes are optional: {key: [3, 2, 1, takeoff]}
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#######################
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# EXTRA YAML FEATURES #
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#######################
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# YAML also has a handy feature called 'anchors', which let you easily duplicate
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# content across your document. Both of these keys will have the same value:
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anchored_content: &anchor_name This string will appear as the value of two keys.
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other_anchor: *anchor_name
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# Anchors can be used to duplicate/inherit properties
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base: &base
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name: Everyone has same name
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foo: &foo
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<<: *base
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age: 10
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bar: &bar
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<<: *base
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age: 20
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# foo and bar would also have name: Everyone has same name
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# YAML also has tags, which you can use to explicitly declare types.
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explicit_string: !!str 0.5
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# Some parsers implement language specific tags, like this one for Python's
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# complex number type.
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python_complex_number: !!python/complex 1+2j
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# We can also use yaml complex keys with language specific tags
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? !!python/tuple [5, 7]
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: Fifty Seven
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# Would be {(5, 7): 'Fifty Seven'} in Python
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####################
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# EXTRA YAML TYPES #
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####################
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# Strings and numbers aren't the only scalars that YAML can understand.
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# ISO-formatted date and datetime literals are also parsed.
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datetime: 2001-12-15T02:59:43.1Z
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datetime_with_spaces: 2001-12-14 21:59:43.10 -5
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date: 2002-12-14
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# The !!binary tag indicates that a string is actually a base64-encoded
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# representation of a binary blob.
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gif_file: !!binary |
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R0lGODlhDAAMAIQAAP//9/X17unp5WZmZgAAAOfn515eXvPz7Y6OjuDg4J+fn5
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OTk6enp56enmlpaWNjY6Ojo4SEhP/++f/++f/++f/++f/++f/++f/++f/++f/+
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+f/++f/++f/++f/++f/++SH+Dk1hZGUgd2l0aCBHSU1QACwAAAAADAAMAAAFLC
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AgjoEwnuNAFOhpEMTRiggcz4BNJHrv/zCFcLiwMWYNG84BwwEeECcgggoBADs=
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# YAML also has a set type, which looks like this:
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set:
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? item1
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? item2
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? item3
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or: {item1, item2, item3}
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# Like Python, sets are just maps with null values; the above is equivalent to:
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set2:
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item1: null
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item2: null
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item3: null
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```
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### More Resources
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+ [YAML official website](http://yaml.org/)
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+ [Online YAML Validator](http://codebeautify.org/yaml-validator)
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