RHCE8 资料整理（十一）

第 32 章 控制语句

一个play中可以包含多个task，如果不想所有的task全部执行，可以设置只有满足某个条件才执行这个task。本章主要介绍when和block-rescue两种判断语句。

32.1 判断语句 when

when作为一个判断语句，出现在某个task下，格式，

tasks:
- name: xxx
  模块
  when: 条件

如果条件成立，则执行模块，否则不执行。

在when中引用变量时是不用加{{}}的

32.1.1 when 判断中>、<、!=和==的使用

when后面可以有多个判断条件，使用or或and作为连接符

常见的判断符包括：

符号	说明
==	等于
!=	不等于
>	大于
=>	大于等于
<	小于
<=	小于等于

[root@node-137 ansible]# cat when-1.yml
---
- hosts: db1
  tasks:
  - name: when test
    debug: msg="1<2"
    when: 1<2
  - name: when test2
    debug: msg="1>2"
    when: 1>2
  - debug: msg="1>2 or 2<3"
    when: 1>2 or 2<3
  - debug: msg="2>1 and 3>2"
    when: 2>1 and 3>2
  - debug: msg="centos:7"
    when: ansible_distribution_major_version=="7"
[root@node-137 ansible]# ansible-playbook when-1.yml

PLAY [db1] ****************************************************************************************************************************

TASK [Gathering Facts] ****************************************************************************************************************
ok: [node-138]

TASK [when test] **********************************************************************************************************************
ok: [node-138] => {
    "msg": "1<2"
}

TASK [when test2] *********************************************************************************************************************
skipping: [node-138]

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "1>2 or 2<3"
}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "2>1 and 3>2"
}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "centos:7"
}

PLAY RECAP ****************************************************************************************************************************
node-138                   : ok=5    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0

当判断条件不成立，则会提示skipping

32.1.2 when 判断中 in的用法

在when语句中，除可以使用上面的大于、小于等判断方法外，还可以使用in，如下

value [not] in 列表

如果此值在这个列表中，则判断成立，否则不成立

[root@node-137 ansible]# cat when-3.yml
---
- hosts: db1
  gather_facts: false
  vars:
    list1: [1,2,3,4,5]
  tasks:
  - debug: msg="123"
    when: 1 in list1
  - debug: msg="not in"
    when: 6 not in list1
[root@node-137 ansible]# ansible-playbook when-3.yml

PLAY [db1] ****************************************************************************************************************************

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "123"
}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "not in"
}

PLAY RECAP ****************************************************************************************************************************
node-138                   : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

32.1.3 when 判断中 is的用法

is可以用于判断变量是否被定义，常见的判断包括以下3种：

1. is defined，变量被定义
2. is undefined，变量未被定义，等同于is not defined
3. is noe，变量被定义了，但值为空

[root@node-137 ansible]# cat when-4.yml
---
- hosts: db1
  gather_facts: true
  vars:
    aa: 123
    dd:
  tasks:
  - debug: msg={{aa}}
    when: aa is defined
  - debug: msg="bb"
    when: bb is not defined
  - debug: msg="cc"
    when: cc is undefined
  - debug: msg="dd"
    when: dd is none
[root@node-137 ansible]# ansible-playbook when-4.yml

PLAY [db1] ****************************************************************************************************************************

TASK [Gathering Facts] ****************************************************************************************************************
ok: [node-138]

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": 123
}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "bb"
}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "cc"
}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "dd"
}

PLAY RECAP ****************************************************************************************************************************
node-138                   : ok=5    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

判断文件的小练习

[root@node-137 ansible]# cat when-5.yml
---
- hosts: db1
  tasks:
  - name: run syscmd
    shell: "ls /aa.txt"
    register: aa
    ignore_errors: true
  - name: task2
    fail: msg="命令执行错误"
    when: aa.rc != 0
  - name: task3
    debug: msg="OK123"
[root@node-137 ansible]# ansible-playbook when-5.yml

PLAY [db1] ****************************************************************************************************************************

TASK [Gathering Facts] ****************************************************************************************************************
ok: [node-138]

TASK [run syscmd] *********************************************************************************************************************
fatal: [node-138]: FAILED! => {"changed": true, "cmd": "ls /aa.txt", "delta": "0:00:00.037543", "end": "2023-12-20 21:02:05.426760", "msg": "non-zero return code", "rc": 2, "start": "2023-12-20 21:02:05.389217", "stderr": "ls: cannot access /aa.txt: No such file or directory", "stderr_lines": ["ls: cannot access /aa.txt: No such file or directory"], "stdout": "", "stdout_lines": []}
...ignoring

TASK [task2] **************************************************************************************************************************
fatal: [node-138]: FAILED! => {"changed": false, "msg": "命令执行错误"}

PLAY RECAP ****************************************************************************************************************************
node-138                   : ok=2    changed=1    unreachable=0    failed=1    skipped=0    rescued=0    ignored=1

32.2 判断语句 block-rescue

对于when来说，只能做一个判断，成立就执行，不成立就不执行。block和rescue一般同用，类似于shell判断语句中的if-else，在block下面可以包含多个模块，来判断这多个模块是否执行成功。用法，

block:
- 模块1
- 模块2
- 模块3
rescue:
- 模块4
- 模块5

执行流程：

• 首先执行task1的block中的模块1，如果成功，则继续执行block中的模块2，如果block中所有模块均执行成功，则跳过rescue中的模块，进而执行task2中的模块
• 当执行task1的block中的某个模块失败，则执行rescue中的模块4，如果rescue中的所有模块均执行成功，则继续执行task2中的模块，如果rescue中的某个模块失败，则退出playbook
• 如果block或rescue的模块中，有ignore_errors: yes选项，则会忽略该报错模块

示例1，参考图1

[root@node-137 ansible]# cat block-1.yml
---
- hosts: db1
  tasks:
  - name: task1
    block:
    - debug: msg="block1"
    - shell: "ls /"
    - debug: msg="block2"
    rescue:
    - debug: msg="rescue1"
    - debug: msg="rescue2"
  - name: task2
    debug: msg="task2"
    
[root@node-137 ansible]# ansible-playbook block-1.yml

PLAY [db1] ****************************************************************************************************************************

TASK [Gathering Facts] ****************************************************************************************************************
ok: [node-138]

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "block1"
}

TASK [shell] **************************************************************************************************************************
changed: [node-138]

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "block2"
}

TASK [task2] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "task2"
}

PLAY RECAP ****************************************************************************************************************************
node-138                   : ok=5    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

示例2，参考图2

[root@node-137 ansible]# cat block-1.yml
---
- hosts: db1
  tasks:
  - name: task1
    block:
    - debug: msg="block1"
    - shell: "ls /aa.txt"
    - debug: msg="block2"
    rescue:
    - debug: msg="rescue1"
    - debug: msg="rescue2"
  - name: task2
    debug: msg="task2"
[root@node-137 ansible]# ansible-playbook block-1.yml

PLAY [db1] ****************************************************************************************************************************

TASK [Gathering Facts] ****************************************************************************************************************
ok: [node-138]

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "block1"
}

TASK [shell] **************************************************************************************************************************
fatal: [node-138]: FAILED! => {"changed": true, "cmd": "ls /aa.txt", "delta": "0:00:00.032879", "end": "2023-12-20 21:52:57.557622", "msg": "non-zero return code", "rc": 2, "start": "2023-12-20 21:52:57.524743", "stderr": "ls: cannot access /aa.txt: No such file or directory", "stderr_lines": ["ls: cannot access /aa.txt: No such file or directory"], "stdout": "", "stdout_lines": []}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "rescue1"
}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "rescue2"
}

TASK [task2] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "task2"
}

PLAY RECAP ****************************************************************************************************************************
node-138                   : ok=5    changed=0    unreachable=0    failed=0    skipped=0    rescued=1    ignored=0

示例3，参考图3

[root@node-137 ansible]# cat block-1.yml
---
- hosts: db1
  tasks:
  - name: task1
    block:
    - debug: msg="block1"
    - shell: "ls /aa.txt"
      ignore_errors: true
    - debug: msg="block2"
    rescue:
    - debug: msg="rescue1"
    - debug: msg="rescue2"
  - name: task2
    debug: msg="task2"
[root@node-137 ansible]# ansible-playbook block-1.yml

PLAY [db1] ****************************************************************************************************************************

TASK [Gathering Facts] ****************************************************************************************************************
ok: [node-138]

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "block1"
}

TASK [shell] **************************************************************************************************************************
fatal: [node-138]: FAILED! => {"changed": true, "cmd": "ls /aa.txt", "delta": "0:00:00.035454", "end": "2023-12-20 21:56:08.510199", "msg": "non-zero return code", "rc": 2, "start": "2023-12-20 21:56:08.474745", "stderr": "ls: cannot access /aa.txt: No such file or directory", "stderr_lines": ["ls: cannot access /aa.txt: No such file or directory"], "stdout": "", "stdout_lines": []}
...ignoring

TASK [debug] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "block2"
}

TASK [task2] **************************************************************************************************************************
ok: [node-138] => {
    "msg": "task2"
}

PLAY RECAP ****************************************************************************************************************************
node-138                   : ok=5    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=1

32.3 循环语句

在playbook中用loop来循环列表中的元素，在loop中，使用一个固定的变量item，然后把每个元素赋值给item。格式，

list1: [a,b,c]
...
debug: msg={{item}}
loop: "{{list1}}"
#或 
#with_items: "{{list1}}"

• 这里关键字loop可以替换为with_items，含义相同
• loop或with_items后面的{{}}需要使用""双引号或''单引号引起来

[root@node-137 ansible]# cat loop-1.yml
---
- hosts: db1
  gather_facts: false
  vars:
    users:
    - uname: "tom"
      age: 18
    - uname: "jerry"
      age: 19
    - uname: "jacky"
      age: 18
  tasks:
  - debug: msg={{ item }}
    with_items: "{{users}}"
  - debug: msg={{item.uname}}
    loop: '{{users}}'
  - debug: msg={{item}}
    when: item.age == 18
    loop: "{{users}}"
[root@node-137 ansible]# ansible-playbook loop-1.yml

PLAY [db1] ****************************************************************************************************************************

TASK [debug] **************************************************************************************************************************
ok: [node-138] => (item={u'uname': u'tom', u'age': 18}) => {
    "msg": {
        "age": 18,
        "uname": "tom"
    }
}
ok: [node-138] => (item={u'uname': u'jerry', u'age': 19}) => {
    "msg": {
        "age": 19,
        "uname": "jerry"
    }
}
ok: [node-138] => (item={u'uname': u'jacky', u'age': 18}) => {
    "msg": {
        "age": 18,
        "uname": "jacky"
    }
}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => (item={u'uname': u'tom', u'age': 18}) => {
    "msg": "tom"
}
ok: [node-138] => (item={u'uname': u'jerry', u'age': 19}) => {
    "msg": "jerry"
}
ok: [node-138] => (item={u'uname': u'jacky', u'age': 18}) => {
    "msg": "jacky"
}

TASK [debug] **************************************************************************************************************************
ok: [node-138] => (item={u'uname': u'tom', u'age': 18}) => {
    "msg": {
        "age": 18,
        "uname": "tom"
    }
}
skipping: [node-138] => (item={u'uname': u'jerry', u'age': 19})
ok: [node-138] => (item={u'uname': u'jacky', u'age': 18}) => {
    "msg": {
        "age": 18,
        "uname": "jacky"
    }
}

PLAY RECAP ****************************************************************************************************************************
node-138                   : ok=3    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

在最后一个task中，加入判断语句when，使age等于18的user进行打印

with_items还能够迭代字典，而loop不行

[root@node-137 ansible]# cat loop-1.yml
---
- hosts: db1
  gather_facts: false
  vars:
    userdict:
      users:
        uname: "tom"
        age: 18
        age1: 18
      users2:
        uname: "jea"
        age: 19
        age1: 20
  tasks:
  - debug: msg={{ item }}
    ignore_errors: true
    with_items: "{{userdict.users}}"
  - debug: msg={{ item }}
    loop: "{{userdict}}"
[root@node-137 ansible]# ansible-playbook loop-1.yml

PLAY [db1] ****************************************************************************************************************************

TASK [debug] **************************************************************************************************************************
ok: [node-138] => (item=uname) => {
    "msg": "uname"
}
ok: [node-138] => (item=age) => {
    "msg": "age"
}
ok: [node-138] => (item=age1) => {
    "msg": "age1"
}

TASK [debug] **************************************************************************************************************************
fatal: [node-138]: FAILED! => {"msg": "Invalid data passed to 'loop', it requires a list, got this instead: {u'users2': {u'uname': u'jea', u'age': 19, u'age1': 20}, u'users': {u'uname': u'tom', u'age': 18, u'age1': 18}}. Hint: If you passed a list/dict of just one element, try adding wantlist=True to your lookup invocation or use q/query instead of lookup."}

PLAY RECAP ****************************************************************************************************************************
node-138                   : ok=1    changed=0    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0