YAML的誕生不算太晚, 1.0在2004就出了, 雖然晚了JSON 5年(1999年), 但算是蠻迅速就被開發者們給接受了
相較於INI, YAML所支持的層級, 資料類型可就豐富了,
支持的結構也從來到3種(Mapping、Collection、Scalars)
它主檔的口號如下
YAML Ain't Markup Language
YAML is a human friendly data serialization
language for all programming languages.
第一句YAML Ain't Markup Language就是YAML全名了
就是希望全程式語言都能用, 對人類好閱讀跟設計.
YAML有幾個特徵
Tab不支持, 但IDE會幫忙轉成對應的Space
parent:
son1: 1 #2個space
son2: #因為想要同層級, 所以同上是2個space
grandson: 3 #4個space
sonofgrandson: #因為想要同層級, 所以同上是4個space
grandgrandson: 4 #隨意個space, 反正比4多
轉成對應的JSON
{ "parent": { "son1": 1, "son2": { "grandson": 3, "sonofgrandson": { "grandgrandson": 4 } } } }
Case sensitive, 大小寫不同視為不同變數
A: 1
a: 1
# 註解, 後面整行都是註解, 隨時都能加入註解'或"包起來, 除非有必要!!, 但我其實自己不懂這有什麼實際用途---為開始, ...為document的結束---與...來撰寫---
# 1nd document
ithome: 12th
...
---
# 2nd document
ithome: 13th
...
YAML的基本資料節點
ithome:
strings:
- Hi eveny iron man
year: 2021
finished: False
beginDate: 2021-09-01
nullType:
轉成對應的JSON
{ "ithome": { "strings": [ "Hi eveny iron man" ], "year": 2021, "finished": false, "beginDate": "2021-09-01T00:00:00.000Z", "nullType": null } }
-或[]表示ithome:
years:
- 2021
- 2020
- 2019
terms: [13th, 12th, 11th]
轉成對應的JSON
{ "ithome": { "years": [ 2021, 2020 ], "terms": [ "13th", "12th" ] } }
key: value
String類型的幾種多行寫法與indicators:|與>
先看sample
preserved: |
65 Home Runs
0.278 Batting Average
Mark McGwire's
year was crippled
folded: >
Your long
string here.
Second string here.
Last string here.
轉成對應的JSON
{ preserved: '65 Home Runs\n0.278 Batting Average\n Mark McGwire\'s\n year was crippled\n', folded: 'Sammy Sosa completed another fine season with great stats.\n\n 63 Home Runs\n 0.288 Batting Average\n\nWhat a year!\n' }
|只要碰到yaml換行就是換行, 然後之後其他行是對齊第一行的indent, 但若是自己多打的額外indent則會被保留, 像是 Mark McGwire's跟第一行相比多縮進的兩個space, 就會被保留.
>換行方式比較特別, 要遇到空白行, 會把前一句的\n給修剪掉, 並且在最後輸出一個\n
可以看到第一個\n出現在Second前面, 因為第一個here後面有一個\n(這個被移除), 然後接一個空白行\n.
第二句最後轉出json是\n\n, 第二個here後面的\n一樣被移除, 接兩個空白行\n\n, 就輸出這兩個了
|或>搭配+或是-+就是最後多加個\n-反之就是最後把最後的\n刪除
preserved: |
12th
13th
preservedPlu: |+
12th
13th
preservedMinus: |-
12th
13th
{ preserved: '12th\n13th\n',
preservedPlu: '12th\n13th\n\n',
preservedMinus: '12th\n13th' }
當Yaml文件中, 有多處的重複內容時, 可以透過Anchor與Alias來快速引用相同的內容.
在字串類型上的應用, 當對同一個Anchor名稱定義內容時, 能做覆寫
ithome: &anchor |
11th
12th
reuseFirst: *anchor
override: &anchor |
12th
13th
reuseSecond: *anchor
{ ithome: '11th\n12th\n',
reuseFirst: '11th\n12th\n',
override: '12th\n13th\n',
reuseSecond: '12th\n13th\n' }
陣列元素的重複引用
---
hr:
- Mark McGwire
# Following node labeled SS
- &SS Sammy Sosa
rbi:
- *SS # Subsequent occurrence
- Ken Griffey
{ hr: [ 'Mark McGwire', 'Sammy Sosa' ],
rbi: [ 'Sammy Sosa', 'Ken Griffey' ] }
於mapping類型的應用
這裡會看到<<這個符號, 這是用來merge mapping的key
當如果需要修改原本的key, 或者新增key,
就需要<<來merge, 如果只是純引用, 則不必
defaults: &defaults
year: 2021
terms: 13th
name: iT邦幫忙
development:
*defaults
newFeature:
<<: *defaults
name: iT邦個忙
{ defaults: { year: 2021, terms: '13th', name: 'iT邦幫忙' },
development: { year: 2021, terms: '13th', name: 'iT邦幫忙' },
newFeature: { year: 2021, terms: '13th', name: 'iT邦個忙' } }
現在最常見到YAML的應用場景
大概就是Docker-Compose文件與K8S文件
範例來源DoockerCompose
version: "3.9"
x-volumes:
&default-volume # Anchor宣告
driver: foobar-storage
services:
web:
image: myapp/web:latest
volumes: ["vol1", "vol2", "vol3"]
volumes:
vol1: *default-volume # 引用Anchor
vol2:
<< : *default-volume # 引用Anchor並Merge keys
name: volume02
vol3:
<< : *default-volume # 引用Anchor並Merge keys
driver: default
name: volume-local
{ version: '3.9',
'x-volumes': { driver: 'foobar-storage' },
services:
{ web:
{ image: 'myapp/web:latest',
volumes: [ 'vol1', 'vol2', 'vol3' ] } },
volumes:
{ vol1: { driver: 'foobar-storage' },
vol2: { driver: 'foobar-storage', name: 'volume02' },
vol3: { driver: 'default', name: 'volume-local' } } }
YAML具有多種Type的表示, 也能透過Anchor達到內容覆用.
但其實蠻複雜的XD, 目前在WebService的傳輸協議上, 可見度很低, 幾乎還是JSON居多.
但作為像Docker-compose或k8s這種需要多組服務的設定時,
確實比起上一篇的ini, 更能表現出複雜設定時的便利性
ps. YAML 1.2.2 於2021/10/1號剛好釋出了
iThome鐵人賽
看影片追技術