如何在 when 条件中使用变量替换? [英] How to use variable substitution in a when condition?

问题描述

我是一个新的 ansible 用户.我在任务的 when 条件中需要一个变量.我正在尝试使用定义为 home_directory 的 home_directory 变量:"{{ ansible_env.HOME }}"在 vars/main.yaml 文件中.

I'm a new ansible user. I need a variable in a task's when condition. I am trying to use home_directory variable, which is defined as home_directory: "{{ ansible_env.HOME }}" in the vars/main.yaml file.

我尝试使用以下内容:

when: {{ home_directory}}/var_name['var_key'] != command_output['stdout']

when: {{ home_directory}}/var_name['var_key'] != command_output['stdout']

然而，我后来发现 jinja 模板 {{}} 或 {%%} 在当条件.我也试过不带引号和 {{}} 的条件，但 home_directory 值是在 when 条件下不被替换.

However, I later found out that jinja templates {{}} or {%%} are not allowed/recommended in the when condition. I also tried condition without quotes and {{}} but home_directory value is not being replaced in the when condition.

有人能告诉我我可以在这里做什么吗?

Could someone please tell me what I can do here?

推荐答案

但是，我后来发现在 when 条件中不允许/推荐使用 jinja 模板 {{}} 或 {%%}.

However, I later found out that jinja templates {{}} or {%%} are not allowed/recommended in the when condition.

这是因为 when 的参数是在隐式模板上下文中计算的.换句话说，在 {{...}} 标记中准确地写下您将要写的内容，但您不需要标记，因为上下文是命令的固有内容.

This is because the arguments to when are evaluated in an implicit template context. In other words, write exactly what you would write inside {{...}} markers, but you don't need the markers because the context is intrinsic to the command.

换句话说，不是:

when: {{ home_directory}}/var_name['var_key'] != command_output['stdout']

写:

when: home_directory ~ "/" ~ var_name['var-key'] != command_output['stdout']

其中 ~ 是 Jinja 字符串连接运算符.

Where ~ is the Jinja string concatenation operator.

我们可以稍微简化一下:

We can simplify that a bit:

when: "%s/%s" % (home_directory, var_name.var_key) != command_output.stdout

这利用 Linux 字符串格式化语法将变量替换为字符串.

This takes advantage of Linux string formatting syntax to substitute variables into a string.

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