# Field reference in ruby filter

**URL:** <https://discuss.elastic.co/t/field-reference-in-ruby-filter/97527>\
**Category:** Logstash\
**Created:** [August 18, 2017, 8:10am UTC](https://discuss.elastic.co/t/field-reference-in-ruby-filter/97527 "2017-08-18T08:10:50Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Robert\_Kovacs](https://avatars.discourse-cdn.com/v4/letter/r/4491bb/32.png) [@Robert\_Kovacs](https://discuss.elastic.co/u/Robert_Kovacs)\
**Post date:** [August 18, 2017, 8:10am UTC](https://discuss.elastic.co/t/field-reference-in-ruby-filter/97527/1 "2017-08-18T08:10:50Z")

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Is it possible to reference a field inside the ruby filters code?  
I have a field with an ID and I would like to create a variable for each of it's values if it has not been created yet, or do something with it, if I already created it.  
Something like this:  
ruby {  
code =\>  
"if defined? $my\_var%{my\_ID} == nil  
$my\_var%{my\_ID} = 0;  
else  
do stuff with $my\_var%{my\_ID}  
end"  
}

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<div class="post-metadata">

**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:** [August 18, 2017, 8:58am UTC](https://discuss.elastic.co/t/field-reference-in-ruby-filter/97527/2 "2017-08-18T08:58:02Z")

</div>

[https://www.elastic.co/guide/en/logstash/current/event-api.html](https://www.elastic.co/guide/en/logstash/current/event-api.html)

---

<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:** [September 15, 2017, 8:58am UTC](https://discuss.elastic.co/t/field-reference-in-ruby-filter/97527/3 "2017-09-15T08:58:27Z")

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