如何让 Ansible 解释变量内的变量? [英] How can I make Ansible interpret a variable inside a variable?

问题描述

每当我试图让 Ansible 解释一个嵌套变量时——所以，一个变量在另一个变量中——我无法得到我期望的结果.

Whenever I try to make Ansible interpret a nested variable — so, a variable inside another variable — I cannot get the result I expect.

给定变量:

key: bar
foo:
  bar: baz
foo_bar: baz

我已经尝试了这三种方法，但没有多少运气来动态访问字典 foo 的键 bar 或键 foo_bar，在构造时来自 key 的值:

I have tried those three approaches without much luck to dynamically access the key bar of the dictionary foo or the key foo_bar, when constructed from the value of key:

- ansible.builtin.debug:
    msg: "{{ foo[{{ key }}] }}"

但是，我收到错误:

'模板字符串模板错误:预期标记'':''，得到''}''.字符串:{{ foo[{{ key }}] }}'

'template error while templating string: expected token '':'', got ''}''. String: {{ foo[{{ key }}] }}'

- ansible.builtin.debug:
      msg: "{{ foo_{{ key }} }}"

但是，我遇到了类似的错误

But, I get a similar error

'模板字符串模板错误:预期标记''打印语句结束''，得到''{''.字符串:{{foo_{{key}}}}'

'template error while templating string: expected token ''end of print statement'', got ''{''. String: {{ foo_{{ key }} }}'

- ansible.builtin.debug:
    msg: "{{ foo['{{ key }}'] }}"

在这里，我得到了错误

该任务包括一个带有未定义变量的选项.错误是:'dict object' 没有属性 '{{ key }}'

The task includes an option with an undefined variable. The error was: 'dict object' has no attribute '{{ key }}'

我期望得到 foo.bar 或 foo_bar 的值，所以 baz.
实现这一目标的正确方法是什么?

I was expecting to get the value of foo.bar or foo_bar, so baz.
What would be the correct approach to achieve this?

推荐答案

如 Ansible 的常见问题所述，小胡子不堆叠.

As advised in the Frequently Asked Questions of Ansible, moustache do not stack.

另一条规则是胡须不能堆叠".我们经常看到这个:

Another rule is ‘moustaches don’t stack’. We often see this:

{{ somevar_{{other_var}} }}

以上不符合您的预期，如果您需要使用动态变量，请酌情使用以下内容:

The above DOES NOT WORK as you expect, if you need to use a dynamic variable use the following as appropriate:

{{ hostvars[inventory_hostname]['somevar_' + other_var] }}

对于非主机变量"，您可以使用 vars 查找 插件:

For ‘non host vars’ you can use the vars lookup plugin:

{{ lookup('vars', 'somevar_' + other_var) }}

^{来源:https://docs.ansible.com/ansible/latest/reference_appendices/faq.html#when-should-i-use-also-how-to-interpolate-variables-or-dynamic-variable-names}

因此，有两种情况适用:

So, there are two cases where this will apply:

1. 尝试从变量访问字典的键时，您只需按原样使用该变量，请记住，当您在 表达式分隔符{{ ... }}，一个字符串将被解释为一个变量，如果不能用单引号或双引号括起来.

1. When trying to access a key of a dictionary from a variable, you would simply use the variable as is, remembering that, when you are inside the expression delimiters {{ ... }}, a string will be interpreted as a variable, if not enclosed inside simple or double quotes.

- ansible.builtin.debug:
    msg: "{{ foo[key] }}"
  vars:
    key: bar
    foo:
      bar: baz

尝试从变量构造变量名称或字典键时，您必须使用 连接运算符，~:

- ansible.builtin.debug:
    msg: "{{ foo['foo_' ~ key] }}"
  vars:
    key: bar
    foo:
      foo_bar: baz

您可能还需要使用 vars 查找 或 vars 字典来访问动态变量:

You might also need to use the vars lookup or the vars dictionary to access a dynamic variable:

- ansible.builtin.debug:
    msg: "{{ vars['foo_' ~ key] }}"
  vars:
    key: bar
    foo_bar: baz

---

旁注:由于提出的原因，建议使用正确的连接运算符 ~ 比 Ansible 文档中建议的数学运算符 +在 Jinja 文档中:

---

Side note: it is more advisable to use the right concatenation operator, ~ than the math operator + as advised in the Ansible documentation for the reason raised in Jinja documentation:

通常对象是数字，但如果两者都是字符串或列表，您可以通过这种方式连接它们.然而，这不是连接字符串的首选方式！对于字符串连接，请查看 ~ 运算符.

^{来源:https://jinja.palletsprojects.com/en/2.11.x/templates/#math}

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