# Get logstash to fail on undefined variable

**URL:** <https://discuss.elastic.co/t/get-logstash-to-fail-on-undefined-variable/223320>\
**Category:** Logstash\
**Created:** [March 12, 2020, 11:19am UTC](https://discuss.elastic.co/t/get-logstash-to-fail-on-undefined-variable/223320 "2020-03-12T11:19:05Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![macau](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/macau/32/64091_2.png) [@macau](https://discuss.elastic.co/u/macau)\
**Post date:** [March 12, 2020, 11:19am UTC](https://discuss.elastic.co/t/get-logstash-to-fail-on-undefined-variable/223320/1 "2020-03-12T11:19:05Z")

</div>

```
output {
  file {
    path => "/srv/logstash-logs/%{somevar}.log"
	...

```

How can I get logstash to fail when an undefined variable is encountered?

---

<div class="post-metadata">

**Author:** ![ITIC](https://avatars.discourse-cdn.com/v4/letter/i/90ced4/32.png) [@ITIC](https://discuss.elastic.co/u/ITIC)\
**Post date:** [March 12, 2020, 11:34am UTC](https://discuss.elastic.co/t/get-logstash-to-fail-on-undefined-variable/223320/2 "2020-03-12T11:34:14Z")

</div>

Hi

You could try something like this:

```auto
output {
  if [somevar] {
    file {
      path => "/srv/logstash-logs/%{somevar}.log"
	  ...
	}
  }
  else {
    <whatever you need to do. If nothing, just omit this "else" alltogether>
 }
}

```

Hope this helps.

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [April 9, 2020, 11:34am UTC](https://discuss.elastic.co/t/get-logstash-to-fail-on-undefined-variable/223320/3 "2020-04-09T11:34:22Z")

</div>

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