# Logstash Question

**URL:** <https://discuss.elastic.co/t/logstash-question/83178>\
**Category:** Logstash\
**Created:** [April 21, 2017, 8:52am UTC](https://discuss.elastic.co/t/logstash-question/83178 "2017-04-21T08:52:07Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Daniel69](https://avatars.discourse-cdn.com/v4/letter/d/47e85d/32.png) [@Daniel69](https://discuss.elastic.co/u/Daniel69)\
**Post date:** [April 21, 2017, 8:52am UTC](https://discuss.elastic.co/t/logstash-question/83178/1 "2017-04-21T08:52:07Z")

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Hi,

i have a question about logstash:

I'm duplicating a value to easily parse it into an array like this:

> mutate {  
> add\_field =\> ["[@metadata][MESSAGE\_DB]", "%{MESSAGE}"]  
> }

and then i can parse an array number like that:

> mutate {  
> split =\> { "[@metadata][MESSAGE\_DB]" =\> " " }  
> add\_field =\> ['DB\_INSTANCE','%{[@metadata][MESSAGE\_DB][4]}']  
> }

does its possible to replace de number 4 with a variable NUM\_MESSAGE\_DB ?

like something like that

> add\_field =\> ['DB\_INSTANCE','%{[@metadata][MESSAGE\_DB][%{[NUM\_MESSAGE\_DB]}]}']

thanks for your response

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**Author:** ![magnusbaeck](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/magnusbaeck/32/44943_2.png) [@magnusbaeck](https://discuss.elastic.co/u/magnusbaeck)\
**Post date:** [April 21, 2017, 8:59am UTC](https://discuss.elastic.co/t/logstash-question/83178/2 "2017-04-21T08:59:00Z")

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I don't think you can do that. Why would you want to do that? Maybe there's a better way of parsing your data.

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<div class="post-metadata">

**Author:** ![Daniel69](https://avatars.discourse-cdn.com/v4/letter/d/47e85d/32.png) [@Daniel69](https://discuss.elastic.co/u/Daniel69)\
**Post date:** [April 21, 2017, 9:02am UTC](https://discuss.elastic.co/t/logstash-question/83178/3 "2017-04-21T09:02:43Z")

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NUM\_MESSAGE\_DB is a value from an yml dictionnary,

so it was a way to dynamicaly get another value...

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [May 19, 2017, 9:04am UTC](https://discuss.elastic.co/t/logstash-question/83178/4 "2017-05-19T09:04:58Z")

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