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# 一、基础语法
* only：定义哪些分支和标签的git项目会被执行job
* except：定义哪些分支和标签的git项目将不会被job执行
* rules：允许按照顺序评估规则，知道匹配到并未作业动态提供属性
* workflow
注意：only和except逐渐被抛弃，后续推荐的是使用rules

# 二、实例演示
yaml文件如下：
```yaml
before_script:
  - echo "script in global before script..."

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

variables:
  USERNAME: redrose2100
  PASSWORD: admin123

workflow:
  rules:
    - if: '$USERNAME == "redrose2100"'
      when: always
    - when: never

stages:
  - build
  - test
  - release
  - deploy
  - verify

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

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

build:
  stage: build
  before_script:
    - echo "before script in build..."
    - echo $USERNAME
    - echo $PASSWORD
  script:
    - echo "script in build..."
  after_script:
    - echo "after script in build..."
  tags:
    - docker_in_docker_demo
  rules:
    - if: '$USERNAME == "redrose2100"'
      when: manual
    - if: '$USERNAME == "redrose2200"'
      when: delayed
      start_in: "5"
    - when: on_success

test:
  stage: test
  before_script:
    - echo "before script in test..."
  script:
    - echo "script in test..."
  tags:
    - docker_in_docker_demo
  rules:
    - changes:
        - Dockerfile
      when: manual
  allow_failure: true
  parallel: 5

release:
  stage: release
  script:
    - echo "script in release..."
  after_script:
    - echo "after in release..."
  only:
    - tags
  tags:
    - docker_in_docker_demo
  when: delayed
  start_in: "10"

deploy:
  stage: deploy
  script:
    - echo "script in deploy..."
  tags:
    - docker_in_docker_demo
  when: manual

verify:
  stage: verify
  script: echo "in verify"
  retry: 2
  tags:
    - docker_in_docker_demo

verify-2:
  stage: verify
  script: echo "in verify-2"
  retry:
    max: 2
    when:
      - script_failure
  tags:
    - docker_in_docker_demo
  timeout: 3s
  only:
    - /^dev.*$/
  except:
    - branches
```
执行结果如下所示：
![](/static/upload/20220520_163135.png)

# 三、流水线语法详细解读
## 3.1 only
可用的关键字有，only是指定的执行
![](/static/upload/20220520_163154.png)

如下，将release步骤使用only指定只有打标签的时候才会执行
```yaml
release:
  stage: release
  script:
    - echo "script in release..."
  after_script:
    - echo "after in release..."
  only:
    - tags
  tags:
    - docker_in_docker_demo
  when: delayed
  start_in: "10"
```
当提交代码后，可以看到这里已经没有release步骤了
![](/static/upload/20220520_163218.png)

## 3.2 except
可用的关键字，except是指定的不执行，和only相反
![](/static/upload/20220520_163237.png)

except可以单独指定不执行的标签或分支，也可以和only一起组合使用，如下，即表示只有以dev开头的分支才会执行
```yanl
verify-2:
  stage: verify
  script: echo "in verify-2"
  retry:
    max: 2
    when:
      - script_failure
  tags:
    - docker_in_docker_demo
  timeout: 3s
  only:
    - /^dev.*$/
  except:
    - branches
```
这里因为只有main分支，所有不会执行此步骤，如下：
![](/static/upload/20220520_163255.png)

## 3.3 rules
rules允许按顺序评估单个规则，直到匹配并未作业动态提供属性
注意rules不能与only、except组合使用

rules可用的规则：
* if ：如果条件匹配
* changes：指定文件发生变化
* exists：指定文件存在

如下，使用if语句判断变量USERNAME的值，当是redrose2100时就手动执行，当是redrose2200时就延迟执行，其他情况就是默认之前步骤都成功的时候再执行
```yaml
build:
  stage: build
  before_script:
    - echo "before script in build..."
    - echo $USERNAME
    - echo $PASSWORD
  script:
    - echo "script in build..."
  after_script:
    - echo "after script in build..."
  tags:
    - docker_in_docker_demo
  rules:
    - if: '$USERNAME == "redrose2100"'
      when: manual
    - if: '$USERNAME == "redrose2200"'
      when: delayed
      start_in: "5"
    - when: on_success
```

如下为判断文件是否有修改的，判断Dockerfile是否有修改，如果有修改则手动执行，如果没有修改，则此步骤不执行
```yaml
test:
  stage: test
  before_script:
    - echo "before script in test..."
  script:
    - echo "script in test..."
  tags:
    - docker_in_docker_demo
  rules:
    - changes:
        - Dockerfile
      when: manual
  allow_failure: true
  parallel: 5
```
## 3.4 workflow
顶级workflow关键字适用于整个管道，并将确定是否创建管道
如下，当USERNAME的值为redrose2100时，此时会执行所有的Job，当USERNAME的值修改一下比如redrose2200时，此时整个工作流都不会执行，即没有任何操作，这就是workflow的作用
```yaml
variables:
  USERNAME: redrose2100
  PASSWORD: admin123

workflow:
  rules:
    - if: '$USERNAME == "redrose2100"'
      when: always
    - when: never
```

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