.yml文件格式

http://yaml.org/

YAML: YAML Ain't Markup Language

What It Is: YAML is a human friendly data serialization  standard for all programming languages.

YAML（Yet Another Markup Language）（发音 /ˈjæməl/ ）
 一种基于Unicode容易阅读，容易和脚本语言交互的，用来表达资料序列的编程语言。

 

适应场景

1. 脚本语言：由于实现简单，解析成本很低，YAML 特别适合在脚本语言中使用
2. 序列化： YAML是由宿主语言数据类型直转，的比较适合做序列化。
3. 配置文件：写 YAML 要比写 XML 快得多(无需关注标签或引号)，并且比 INI 文档功能更强。由于兼容性问题，不同语言间的数据流转建议不要用 YAML。

YAML 语法

1. 使用空格 Space 缩进表示分层，不同层次之间的缩进可以使用不同的空格数目，但是同层元素一定左对齐，即前面空格数目相同（不能使用 Tab，各个系统 Tab对应的 Space 数目可能不同，导致层次混乱）
2. ‘#’表示注释，只能单行注释，从#开始处到行尾
3. 破折号后面跟一个空格（a dash and space）表示列表
4. 用冒号和空格表示键值对 key: value
5. 简单数据（scalars，标量数据）可以不使用引号括起来，包括字符串数据。用单引号或者双引号括起来的被当作字符串数据，在单引号或双引号中使用C风格的转义字符

• 大小写敏感
• 使用缩进表示层级关系
• 缩进时不允许使用Tab键，只允许使用空格。
• 缩进的空格数目不重要，只要相同层级的元素左侧对齐即可

 

本文介绍 YAML 的语法，以 JS-YAML 的实现为例。你可以去在线 Demo 验证下面的例子。

YAML 支持的数据结构有三种。

• 对象：键值对的集合，又称为映射（mapping）/ 哈希（hashes） / 字典（dictionary）
• 数组：一组按次序排列的值，又称为序列（sequence） / 列表（list）
• 纯量（scalars）：单个的、不可再分的值

以下分别介绍这三种数据结构。

三、数组

一组连词线开头的行，构成一个数组。

- Cat
- Dog
- Goldfish

转为 JavaScript 如下。

[ 'Cat', 'Dog', 'Goldfish' ]

数据结构的子成员是一个数组，则可以在该项下面缩进一个空格。

-
 - Cat
 - Dog
 - Goldfish

转为 JavaScript 如下。

[ [ 'Cat', 'Dog', 'Goldfish' ] ]

数组也可以采用行内表示法。

animal: [Cat, Dog] 必须要有空格，不然会被解释成字符串。

转为 JavaScript 如下。

{ animal: [ 'Cat', 'Dog' ] }

 

 

使用一个短横线加一个空格代表一个数组项：

hobby:
    - Java
    - LOL

当然也可以有这样的写法：

-
    - Java
    - LOL

可以简单理解为：[[Java,LOL]]

 

valueMapList:  
- name: aaa
age: 21
- name: bbb
age: 31

 

{ valueMapList: [ { name: 'aaa', age: 21 }, { name: 'bbb', age: 31 } ] }

 

Mapping Scalars to Sequences 简单数据列表键值对

american:
- Boston Red Sox
- Detroit Tigers
- New York Yankees
national:
- New York Mets
- Chicago Cubs
- Atlanta Braves

 

 

 

对象

使用冒号代表，格式为key: value。冒号后面要加一个空格：

key: value

可以使用缩进表示层级关系；

key: 
    child-key: value
    child-key2: value2

YAML中还支持流式(flow)语法表示对象，比如上面例子可以写为：

key: {child-key: value, child-key2: value2}

较为复杂的对象格式，可以使用问号加一个空格代表一个复杂的key，配合一个冒号加一个空格代表一个value：

?  
    - complexkey1
    - complexkey2
:
    - complexvalue1
    - complexvalue2

意思即对象的属性是一个数组[complexkey1,complexkey2]，对应的值也是一个数组[complexvalue1,complexvalue2]

 

 引用

锚点&和别名*，可以用来引用。

defaults: &defaults
  adapter:  postgres
  host:     localhost

development:
  database: myapp_development
  <<: *defaults

test:
  database: myapp_test
  <<: *defaults

等同于下面的代码。

defaults:
  adapter:  postgres
  host:     localhost

development:
  database: myapp_development
  adapter:  postgres
  host:     localhost

test:
  database: myapp_test
  adapter:  postgres
  host:     localhost

&用来建立锚点（defaults），<<表示合并到当前数据，*用来引用锚点。

---  # document start

# Comments in YAML look like this.

################
# SCALAR TYPES #
################

# Our root object (which continues for the entire document) will be a map,
# which is equivalent to a dictionary, hash or object in other languages.
key: value
another_key: Another value goes here.
a_number_value: 100
scientific_notation: 1e+12
# The number 1 will be interpreted as a number, not a boolean. if you want
# it to be interpreted as a boolean, use true
boolean: true
null_value: null
key with spaces: value
# Notice that strings don't need to be quoted. However, they can be.
however: 'A string, enclosed in quotes.'
'Keys can be quoted too.': "Useful if you want to put a ':' in your key."
single quotes: 'have ''one'' escape pattern'
double quotes: "have many: \", \0, \t, \u263A, \x0d\x0a == \r\n, and more."
# UTF-8/16/32 characters need to be encoded
Superscript two: \u00B2

# Multiple-line strings can be written either as a 'literal block' (using |),
# or a 'folded block' (using '>').
literal_block: |
    This entire block of text will be the value of the 'literal_block' key,
    with line breaks being preserved.

    The literal continues until de-dented, and the leading indentation is
    stripped.

        Any lines that are 'more-indented' keep the rest of their indentation -
        these lines will be indented by 4 spaces.
folded_style: >
    This entire block of text will be the value of 'folded_style', but this
    time, all newlines will be replaced with a single space.

    Blank lines, like above, are converted to a newline character.

        'More-indented' lines keep their newlines, too -
        this text will appear over two lines.

####################
# COLLECTION TYPES #
####################

# Nesting uses indentation. 2 space indent is preferred (but not required).
a_nested_map:
  key: value
  another_key: Another Value
  another_nested_map:
    hello: hello

# Maps don't have to have string keys.
0.25: a float key

# Keys can also be complex, like multi-line objects
# We use ? followed by a space to indicate the start of a complex key.
? |
  This is a key
  that has multiple lines
: and this is its value

# YAML also allows mapping between sequences with the complex key syntax
# Some language parsers might complain
# An example
? - Manchester United
  - Real Madrid
: [2001-01-01, 2002-02-02]

# Sequences (equivalent to lists or arrays) look like this
# (note that the '-' counts as indentation):
a_sequence:
  - Item 1
  - Item 2
  - 0.5  # sequences can contain disparate types.
  - Item 4
  - key: value
    another_key: another_value
  -
    - This is a sequence
    - inside another sequence
  - - - Nested sequence indicators
      - can be collapsed

# Since YAML is a superset of JSON, you can also write JSON-style maps and
# sequences:
json_map: {"key": "value"}
json_seq: [3, 2, 1, "takeoff"]
and quotes are optional: {key: [3, 2, 1, takeoff]}

#######################
# EXTRA YAML FEATURES #
#######################

# YAML also has a handy feature called 'anchors', which let you easily duplicate
# content across your document. Both of these keys will have the same value:
anchored_content: &anchor_name This string will appear as the value of two keys.
other_anchor: *anchor_name

# Anchors can be used to duplicate/inherit properties
base: &base
  name: Everyone has same name

# The regexp << is called Merge Key Language-Independent Type. It is used to
# indicate that all the keys of one or more specified maps should be inserted
# into the current map.

foo:
  <<: *base
  age: 10

bar:
  <<: *base
  age: 20

# foo and bar would also have name: Everyone has same name

# YAML also has tags, which you can use to explicitly declare types.
explicit_string: !!str 0.5
# Some parsers implement language specific tags, like this one for Python's
# complex number type.
python_complex_number: !!python/complex 1+2j

# We can also use yaml complex keys with language specific tags
? !!python/tuple [5, 7]
: Fifty Seven
# Would be {(5, 7): 'Fifty Seven'} in Python

####################
# EXTRA YAML TYPES #
####################

# Strings and numbers aren't the only scalars that YAML can understand.
# ISO-formatted date and datetime literals are also parsed.
datetime: 2001-12-15T02:59:43.1Z
datetime_with_spaces: 2001-12-14 21:59:43.10 -5
date: 2002-12-14

# The !!binary tag indicates that a string is actually a base64-encoded
# representation of a binary blob.
gif_file: !!binary |
  R0lGODlhDAAMAIQAAP//9/X17unp5WZmZgAAAOfn515eXvPz7Y6OjuDg4J+fn5
  OTk6enp56enmlpaWNjY6Ojo4SEhP/++f/++f/++f/++f/++f/++f/++f/++f/+
  +f/++f/++f/++f/++f/++SH+Dk1hZGUgd2l0aCBHSU1QACwAAAAADAAMAAAFLC
  AgjoEwnuNAFOhpEMTRiggcz4BNJHrv/zCFcLiwMWYNG84BwwEeECcgggoBADs=

# YAML also has a set type, which looks like this:
set:
  ? item1
  ? item2
  ? item3
or: {item1, item2, item3}

# Sets are just maps with null values; the above is equivalent to:
set2:
  item1: null
  item2: null
  item3: null

...  # document end

 

 

 https://www.ruanyifeng.com/blog/2016/07/yaml.html

 https://learnxinyminutes.com/docs/yaml/