blocks|key|569|text|在ansible+docs中:如果没有设置所需的变量，则可以使用JJIA2的已定义测试跳过或失败。例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|570|tasks:

-+shell:+echo+"I've+got+'{{+foo+}}'+and+am+not+afraid+to+use+it!"
++when:+foo+is+defined

-+fail:+msg="Bailing+out.+this+play+requires+'bar'"
++when:+bar+is+not+defined|code-block|syntax|javascript|571|因此，在您的情况下，when:+deployed_revision+is+not+defined应该可以工作|style|CODE|572|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.ansible.com/playbooks_conditionals.html^0|1|C|0|0|0|A|12|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@$A|10|B|11|K|L]]|9|@]|C|$]]|$1|M|3|-4|5|6|7|12|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

From the <a href="https://docs.ansible.com/playbooks_conditionals.html">ansible docs</a>:
If a required variable has not been set, you can skip or fail using Jinja2’s defined test. For example:

<pre><code>tasks:

- shell: echo "I've got '{{ foo }}' and am not afraid to use it!"
 when: foo is defined

- fail: msg="Bailing out. this play requires 'bar'"
 when: bar is not defined
</code></pre>

So in your case, <code>when: deployed_revision is not defined</code> should work

blocks|key|611|text|根据最新的Ansible+version2.5，要检查是否定义了变量，并根据此检查是否要运行任何任务，请使用undefined关键字。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|612|tasks:
++++-+shell:+echo+"I've+got+'{{+foo+}}'+and+am+not+afraid+to+use+it!"
++++++when:+foo+is+defined

++++-+fail:+msg="Bailing+out.+this+play+requires+'bar'"
++++++when:+bar+is+undefined|code-block|syntax|javascript|613|Ansible+Documentation|614|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.ansible.com/ansible/latest/user_guide/playbooks_conditionals.html#the-when-statement^0|1I|9|0|0|0|L|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

As per latest Ansible Version 2.5, to check if a variable is defined and depending upon this if you want to run any task, use <code>undefined</code> keyword.

<pre><code>tasks:
 - shell: echo "I've got '{{ foo }}' and am not afraid to use it!"
 when: foo is defined

 - fail: msg="Bailing out. this play requires 'bar'"
 when: bar is undefined
</code></pre>

<a href="http://docs.ansible.com/ansible/latest/user_guide/playbooks_conditionals.html#the-when-statement" rel="noreferrer">Ansible Documentation</a>

blocks|key|4508326|text|严格声明，您必须检查以下所有项:已定义、非空和非无。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4508327|对于“正常”变量，如果定义并设置或不设置，则会产生差异。请参阅下面示例中的foo和bar。两者都已定义，但仅设置了foo。|offset|length|style|CODE|4508328|另一方面，注册变量被设置为运行命令的结果，并且根据模块的不同而不同。它们大多是json结构。您可能必须检查您感兴趣的子元素。请参见以下示例中的xyz和xyz.msg：|4508329|cat+>+test.yml+<<EOF
-+hosts:+127.0.0.1

++vars:
++++foo:+""++++++++++#+foo+is+defined+and+foo+==+''+and+foo+!=+None
++++bar:+++++++++++++#+bar+is+defined+and+bar+!=+''+and+bar+==+None

++tasks:

++-+debug:
++++++msg+:+""
++++register:+xyz++++#+xyz+is+defined+and+xyz+!=+''+and+xyz+!=+None
+++++++++++++++++++++#+xyz.msg+is+defined+and+xyz.msg+==+''+and+xyz.msg+!=+None

++-+debug:
++++++msg:+"foo+is+defined+and+foo+==+''+and+foo+!=+None"
++++when:+foo+is+defined+and+foo+==+''+and+foo+!=+None

++-+debug:
++++++msg:+"bar+is+defined+and+bar+!=+''+and+bar+==+None"
++++when:+bar+is+defined+and+bar+!=+''+and+bar+==+None

++-+debug:
++++++msg:+"xyz+is+defined+and+xyz+!=+''+and+xyz+!=+None"
++++when:+xyz+is+defined+and+xyz+!=+''+and+xyz+!=+None
++-+debug:
++++++msg:+"{{+xyz+}}"

++-+debug:
++++++msg:+"xyz.msg+is+defined+and+xyz.msg+==+''+and+xyz.msg+!=+None"
++++when:+xyz.msg+is+defined+and+xyz.msg+==+''+and+xyz.msg+!=+None
++-+debug:
++++++msg:+"{{+xyz.msg+}}"
EOF
ansible-playbook+-v+test.yml|code-block|syntax|javascript|4508330|entityMap^0|0|11|3|15|3|1L|3|0|1Z|3|23|7|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]|$D|U|E|V|F|G]|$D|W|E|X|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|Y|8|@$D|Z|E|10|F|G]|$D|11|E|12|F|G]]|9|@]|A|$]]|$1|J|3|K|5|L|7|13|8|@]|9|@]|A|$M|N]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|P|$]]

Strictly stated you must check all of the following: defined, not empty AND not None.

For "normal" variables it makes a difference if defined and set or not set. See <code>foo</code> and <code>bar</code> in the example below. Both are defined but only <code>foo</code> is set.

On the other side registered variables are set to the result of the running command and vary from module to module. They are mostly json structures. You probably must check the subelement you're interested in. See <code>xyz</code> and <code>xyz.msg</code> in the example below:

<pre class="lang-bash prettyprint-override"><code>cat &gt; test.yml &lt;&lt;EOF
- hosts: 127.0.0.1

 vars:
 foo: "" # foo is defined and foo == '' and foo != None
 bar: # bar is defined and bar != '' and bar == None

 tasks:

 - debug:
 msg : ""
 register: xyz # xyz is defined and xyz != '' and xyz != None
 # xyz.msg is defined and xyz.msg == '' and xyz.msg != None

 - debug:
 msg: "foo is defined and foo == '' and foo != None"
 when: foo is defined and foo == '' and foo != None

 - debug:
 msg: "bar is defined and bar != '' and bar == None"
 when: bar is defined and bar != '' and bar == None

 - debug:
 msg: "xyz is defined and xyz != '' and xyz != None"
 when: xyz is defined and xyz != '' and xyz != None
 - debug:
 msg: "{{ xyz }}"

 - debug:
 msg: "xyz.msg is defined and xyz.msg == '' and xyz.msg != None"
 when: xyz.msg is defined and xyz.msg == '' and xyz.msg != None
 - debug:
 msg: "{{ xyz.msg }}"
EOF
ansible-playbook -v test.yml
</code></pre>

I am looking for a way to perform a task when ansible variable is not registers /undefined e.g 

<pre><code>-- name: some task
 command: sed -n '5p' "{{app.dirs.includes}}/BUILD.info" | awk '{print $2}'
 when: (! deployed_revision) AND ( !deployed_revision.stdout )
 register: deployed_revision
</code></pre>

How to run a task when variable is undefined in ansible?

我正在寻找一种方法来执行任务时，可用变量不是寄存器/undefined，例如-- name: some task   command:  sed -n '5p' "{{app.dirs.includes}}/BUILD.info" | awk '{print  $2}'   when: (! deployed_revi...

问如何在ansible中未定义变量的情况下运行任务？
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