在 Ansible 中有条件地定义变量 [英] Conditionally define variable in Ansible

问题描述

我想在 Ansible 剧本中有条件地定义一个变量，如下所示:

I want to conditionally define a variable in an Ansible playbook like this:

my_var: "{{ 'foo' if my_condition}}"

如果条件未解析为 true，我希望变量保持未定义状态.

I would like the variable to remain undefined if the condition does not resolve to true.

如果我尝试执行代码，Ansible 会出现以下错误:

Ansible gives the following error if I try to execute the code:

fatal: [foo.local] => {'msg': 'AnsibleUndefinedVariable: One or more undefined
                       variables: the inline if-expression on line 1 evaluated
                       to false and no else section was defined.', 'failed': True}

为什么这是一个错误?

完整的案例如下所示:

{role: foo, my_var: "foo"}

如果定义了 my_var，角色会做一些特别的事情.在某些情况下，我不希望角色这样做.我可以使用 when:condition，但是我必须复制整个角色块.我也可以使用额外的 bool 变量，但我想要一个无需将接口"更改为角色的解决方案.

If my_var is defined, the role does something special. In some cases, I don't want the role to do this. I could use when: condition, but then I would have to copy the whole role block. I could also use an extra bool variable, but I would like a solution without having to change the "interface" to the role.

有什么想法吗?

推荐答案

你可以这样使用:

my_var: "{{ 'foo' if my_condition else '' }}"

如果条件不匹配，'else' 将发生，在这种情况下，将为变量设置一个空值.我认为这是一个简短、可读且优雅的解决方案.

The 'else' will happen if condition not match, and in this case will set a empty value for the variable. I think this is a short, readable and elegant solution.

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