YAML格式的语法

基本格式

• 用空格缩进, 不能用tab
• 用#标记注释
• 列表: 用短划(-)标记元素
• 映射: 用冒号(:)分隔key, value. 如果写在一行, 需要用逗号分隔并前后加花括号
• 字符串: 不加引号, 加单引号或者加双引号都可以, 加双引号时可以使用\开头的转义字符
• 多行字符串可以用 | 或 > 符号, 紧接着换行符
• 重复的节点, 可以用 & 标识, 并用 * 来引用

基本元素

列表

# 普通
 - Casablanca
 - North by Northwest
 - The Man Who Wasn't There

# 单行
[milk, pumpkin pie, eggs, juice]

men: [John Smith, Bill Jones]
women:
  - Mary Smith
  - Susan Williams

映射

# Indented Block
   name: John Smith
   age: 33
# Inline Block
 {name: John Smith, age: 33}

- {name: John Smith, age: 33}
- name: Mary Smith
  age: 27

多行字符串

data: |
   There once was a short man from Ealing
   Who got on a bus to Darjeeling
       It said on the door
       "Please don't spit on the floor"
   So he carefully spat on the ceiling

data: >
   Wrapped text
   will be folded
   into a single
   paragraph

   Blank lines denote
   paragraph breaks

指定类型

a: 123                     # an integer
b: "123"                   # a string, disambiguated by quotes
c: 123.0                   # a float
d: !!float 123             # also a float via explicit data type prefixed by (!!)
e: !!str 123               # a string, disambiguated by explicit type
f: !!str Yes               # a string via explicit type
g: Yes                     # a boolean True (yaml1.1), string "Yes" (yaml1.2)
h: Yes we have No bananas  # a string, "Yes" and "No" disambiguated by context.

picture: !!binary |
  R0lGODdhDQAIAIAAAAAAANn
  Z2SwAAAAADQAIAAACF4SDGQ
  ar3xxbJ9p0qa7R0YxwzaFME
  1IAADs=

myObject:  !myClass { name: Joe, age: 15 }

另一篇简明的介绍, from https://learnxinyminutes.com/docs/yaml/

---  # 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."

# 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 is used to
# indicate that all the keys of one or more specified maps should be inserted
# into the current map.

foo: &foo
  <<: *base
  age: 10

bar: &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