背景
在学习Fabric的e2e_cli的例子的时候发现很多配置文件都是使用.yaml文件进行配置。虽然看起来结构很简单，但是因为不懂其语法，所以不是很确定其中的具体内容。于是打算简单学习一下。
什么是YAML
第一步，起码要知道其缩写是什么吧，HTML，超文本标记语言，XML，可扩展的标记语言，YAML是什么标记语言呢？
然后，百度告诉我下面两行内容：
YAML是"YAML Ain't a Markup Language"（YAML不是一种置标语言）的递归缩写。
在开发的这种语言时，YAML 的意思其实是："Yet Another Markup Language"（仍是一种置标语言），
真的是简单粗暴，但是这也是我第一次见到递归缩写。然后我去百度看看有没有什么其他的递归缩写，接着我就发现了另外一个很有名的递归缩写，GNU, GNU is Not Unix，当然，GNU就是GNU，一个名字，没有其他含义了。Emacs、GCC都是GNU的产品。
为什么用YAML
话题不扯远了，为什么要用YAML呢？换句话说，YAML有什么特点吸引人呢？
我第一眼看到的e2e_cli的第一步的配置文件的时候，觉得就是简单。
# Copyright IBM Corp. All Rights Reserved.
#
# SPDX-License-Identifier: Apache-2.0
#
# ---------------------------------------------------------------------------
# "OrdererOrgs" - Definition of organizations managing orderer nodes
# ---------------------------------------------------------------------------
OrdererOrgs:
# ---------------------------------------------------------------------------
# Orderer
# ---------------------------------------------------------------------------
- Name: Orderer
Domain: example.com
CA:
Country: US
Province: California
Locality: San Francisco
# ---------------------------------------------------------------------------
# "Specs" - See PeerOrgs below for complete description
# ---------------------------------------------------------------------------
Specs:
- Hostname: orderer
# ---------------------------------------------------------------------------
# "PeerOrgs" - Definition of organizations managing peer nodes
# ---------------------------------------------------------------------------
PeerOrgs:
# ---------------------------------------------------------------------------
# Org1
# ---------------------------------------------------------------------------
- Name: Org1
Domain: org1.example.com
EnableNodeOUs: true
CA:
Country: US
Province: California
Locality: San Francisco
# ---------------------------------------------------------------------------
# "Specs"
# ---------------------------------------------------------------------------
# Uncomment this section to enable the explicit definition of hosts in your
# configuration. Most users will want to use Template, below
#
# Specs is an array of Spec entries. Each Spec entry consists of two fields:
# - Hostname: (Required) The desired hostname, sans the domain.
# - CommonName: (Optional) Specifies the template or explicit override for
# the CN. By default, this is the template:
#
# "{{.Hostname}}.{{.Domain}}"
#
# which obtains its values from the Spec.Hostname and
# Org.Domain, respectively.
# ---------------------------------------------------------------------------
# Specs:
# - Hostname: foo # implicitly "foo.org1.example.com"
# CommonName: foo27.org5.example.com # overrides Hostname-based FQDN set above
# - Hostname: bar
# - Hostname: baz
# ---------------------------------------------------------------------------
# "Template"
# ---------------------------------------------------------------------------
# Allows for the definition of 1 or more hosts that are created sequentially
# from a template. By default, this looks like "peer%d" from 0 to Count-1.
# You may override the number of nodes (Count), the starting index (Start)
# or the template used to construct the name (Hostname).
#
# Note: Template and Specs are not mutually exclusive. You may define both
# sections and the aggregate nodes will be created for you. Take care with
# name collisions
# ---------------------------------------------------------------------------
Template:
Count: 2
# Start: 5
# Hostname: {{.Prefix}}{{.Index}} # default
# ---------------------------------------------------------------------------
# "Users"
# ---------------------------------------------------------------------------
# Count: The number of user accounts _in addition_ to Admin
# ---------------------------------------------------------------------------
Users:
Count: 1
# ---------------------------------------------------------------------------
# Org2: See "Org1" for full specification
# ---------------------------------------------------------------------------
- Name: Org2
Domain: org2.example.com
EnableNodeOUs: true
CA:
Country: US
Province: California
Locality: San Francisco
Template:
Count: 2
Users:
Count: 1
现在让我们把注释去掉，就会看到下面的内容：
OrdererOrgs:
- Name: Orderer
Domain: example.com
CA:
Country: US
Province: California
Locality: San Francisco
Specs:
- Hostname: orderer
PeerOrgs:
- Name: Org1
Domain: org1.example.com
EnableNodeOUs: true
CA:
Country: US
Province: California
Locality: San Francisco
Template:
Count: 2
Users:
Count: 1
- Name: Org2
Domain: org2.example.com
EnableNodeOUs: true
CA:
Country: US
Province: California
Locality: San Francisco
Template:
Count: 2
Users:
Count: 1简单，可读性高，易处理。然后，具体有什么特点呢，专业一点的解释在下面这个简书里提到了，我就不啰嗦了。https://www.jianshu.com/p/da0659a3632b
快速入门
- 首先是三种格式，常量值，对象和数组
比如说Country的值为US
Country: USCA的Country的值为UC
CA:
Country: US
数组,PeerOrgs中有两个Org
PeerOrgs:
- Org1
- Org2
- 一些常量
Count: 1
Country: US
EnableNodeOUs: true #True TRUE true都可以，false也一样
Null: ~ #在YAML中的null使用~来表示
String:
- Hehe
- ‘hello’
- “world”
Date: 2019-01-16
Datetime: 2019-01-16T20:31:15+08:00 #Date加T链接时间在加上时区。
- 注释：
#在YAML中只有单行注释注意：
在YAML中不能有TAB键，只能用空格，2个或者4个，相同层级的要左对齐。
大小写敏感。
冒号后面要加一个空格。代表Key: Value
在数组中也是一个横线后面加一个空格。
见得较少的或者说复杂一点的：
- ---表示一个文档的开始
- …表示一个文档的结束
---
OrdererOrgs:
- Name: Orderer
Domain: example.com
CA:
Country: US
Province: California
Locality: San Francisco
Specs:
- Hostname: orderer
…
- ！！类型转换
String:
- !!str 123456789
- !!str true
- >折叠换行，|保留换行
ZYX: >
This is
Zyx
ZYX: |
This is
Zyx
第一个结果是
This is Zyx
第二个结果是
This is
Zyx
- &锚点，*引用，锚点不能单独写，前面必须有对象名。
Zyx: &zyx This is zyx
Boss: *zyx
结果相当于Boss: This is zyx。
- 锚点可以用在合并内容上
ZYX:
- &Z {x : 1 , y : 2}
Example:
<<: *Z
z: 3
结果为Example = {x = 1 , y =2 , z = 3}
参考：
https://www.jianshu.com/p/3f76188c1a8a
https://www.jianshu.com/p/97222440cd08
https://www.jianshu.com/p/da0659a3632b
https://baike.baidu.com/item/YAML/1067697?fr=aladdin#reference-[1]-1479346-wrap