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[【原文链接】Gitlab----Pipline流水线语法job、script、stages、stage、before_script、after_script、variables、.pre、.post](http://devops-dev.com/article/241)

# 一、最基本的语法
* job ：流水线中额作业
* script：执行的shell命令
* before_script：执行script之前执行
* after_script：在执行script之后执行
* stages：声明步骤，决定了流水线顺序
* stage：指明当前作业属于哪个步骤
* variables： 定义变量

# 二、实例演示
在代码仓创建.gitlab-ci.yml文件，内容如下：
```yaml
before_script:
  - echo "script in global before script..."

after_script:
  - echo "script in global after script..."

variables:
  USERNAME: redrose2100
  PASSWORD: admin123

stages:
  - build
  - test
  - release
  - deploy

setup:
  stage: .pre
  script:
    - echo "script in pre..."

teardown:
  stage: .post
  script:
    - echo "script in post..."

build:
  stage: build
  before_script:
    - echo "before script in build..."
    - echo $USERNAME
    - echo $PASSWORD
  script:
    - echo "script in build..."
  after_script:
    - echo "after script in build..."

test:
  stage: test
  before_script:
    - echo "before script in test..."
  script:
    - echo "script in test..."

release:
  stage: release
  script:
    - echo "script in release..."
  after_script:
    - echo "after in release..."

deploy:
  stage: deploy
  script:
    - echo "script in deploy..."
```

然后提交代码仓，可以得到如下流水线执行结果：
![](https://redrose2100.oss-cn-hangzhou.aliyuncs.com/img/1eef063c-8c2a-11ed-9754-0242ac110002.png)

# 三、流水线详细解读
## 3.1 stages声明执行步骤
不管.gitlab-ci.yml文件中各个作业代码的顺序如何，在执行流水线的时候是按照stages声明的顺序执行，如下stages声明的步骤
```yaml
stages:
  - build
  - test
  - release
  - deploy
```
流水线中顺序与上述声明一致

![](https://redrose2100.oss-cn-hangzhou.aliyuncs.com/img/3a543294-8c2a-11ed-9754-0242ac110002.png)

## 3.2 stage声明当前作业所属的步骤
如下：stage后面声明当前作业属于build步骤，作业名子可以随便定义，但是stage后的步骤名必须在上面stages中声明的，否则会报错
```yaml
build:   # 这里可以随便定义
  stage: build    # 这里必须在上面stages中有声明
  before_script:
    - echo "before script in build..."
    - echo $USERNAME
    - echo $PASSWORD
  script:
    - echo "script in build..."
  after_script:
    - echo "after script in build..."
```

## 3.3 .pre和.post定义前置步骤和后置步骤
如下：stage使用.pre或.post声明，.pre表示此作业在所有作业执行之前执行，.post表示此作业在所有作业执行完成之后再执行
```yaml
setup:
  stage: .pre
  script:
    - echo "script in pre..."

teardown:
  stage: .post
  script:
    - echo "script in post..."
```
执行的结果如下：
![](https://redrose2100.oss-cn-hangzhou.aliyuncs.com/img/52848530-8c2a-11ed-9754-0242ac110002.png)

## 3.4 before_script在script执行之前执行，after_script在script执行之后执行
如下：
```yaml
build:
  stage: build
  before_script:
    - echo "before script in build..."
    - echo $USERNAME
    - echo $PASSWORD
  script:
    - echo "script in build..."
  after_script:
    - echo "after script in build..."
```
查看流水线如下
![](https://redrose2100.oss-cn-hangzhou.aliyuncs.com/img/6286684a-8c2a-11ed-9754-0242ac110002.png)

## 3.5 作业中的before_script和after_script比全局的优先级高
这里是指如果作业中有before_script或者after_script，则执行作业中的before_script和after_script，如果作业中没有，则会执行全局的before_script和after_script
如下：test作业中只有before_script，没有after_script
```yaml
test:
  stage: test
  before_script:
    - echo "before script in test..."
  script:
    - echo "script in test..."
```
查看流水线中执行结果，即执行了当前作业中的before_script，然后执行了全局的after_script
![](https://redrose2100.oss-cn-hangzhou.aliyuncs.com/img/719dd9c6-8c2a-11ed-9754-0242ac110002.png)

## 3.6 variables定义的变量在作业中均可使用
如下定义变量
```yaml
variables:
  USERNAME: redrose2100
  PASSWORD: admin123
```
如下，在build作业中打印变量
![](https://redrose2100.oss-cn-hangzhou.aliyuncs.com/img/873c0cb2-8c2a-11ed-9754-0242ac110002.png)

## 3.7 script即执行shell命令
script即作业的核心内容，主要是通过命令行的方式调用，一般情况下runner为linux，因此这里的script的就是执行shell命令了，因此可以根据实际情况满足各种场景的需求
如下build作业,script中只是打印命令，实际场景中比如编译软件包，安装软件包，部署服务等等均可以做到
```yaml
build:
  stage: build
  before_script:
    - echo "before script in build..."
    - echo $USERNAME
    - echo $PASSWORD
  script:
    - echo "script in build..."
  after_script:
    - echo "after script in build..."
```
build作业的执行结果：
![](https://redrose2100.oss-cn-hangzhou.aliyuncs.com/img/9402fda2-8c2a-11ed-9754-0242ac110002.png)

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