有条件地在Ansible中定义变量

本文介绍了有条件地在Ansible中定义变量的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 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}}"

如果条件不能解析为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}

为什么这仍然是错误?

完整的案例如下:

{role: foo, my_var: "foo"}

如果定义了my_var，则该角色将执行一些特殊的操作.在某些情况下，我不希望该角色执行此操作.我可以使用when: condition，但是随后我将不得不复制整个角色块.我还可以使用一个额外的bool变量，但是我想找到一个解决方案，而不必将角色的接口"更改为.

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

您可以使用以下内容:

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

如果条件不匹配，则将发生'else'，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，易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.