# Logstash Syntax :: Putting the Value of One Field into Another?

**URL:** <https://discuss.elastic.co/t/logstash-syntax-putting-the-value-of-one-field-into-another/208128>\
**Category:** Logstash\
**Created:** [November 15, 2019, 7:41pm UTC](https://discuss.elastic.co/t/logstash-syntax-putting-the-value-of-one-field-into-another/208128 "2019-11-15T19:41:17Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![redapplesonly](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/redapplesonly/32/57700_2.png) [@redapplesonly](https://discuss.elastic.co/u/redapplesonly)\
**Post date:** [November 15, 2019, 7:41pm UTC](https://discuss.elastic.co/t/logstash-syntax-putting-the-value-of-one-field-into-another/208128/1 "2019-11-15T19:41:17Z")

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Hey Logstash Maestros,

I have a syntax question. Suppose I have this as the input data going into Logstash:

```
FieldA FieldB FieldC
==============================
     6 "apples" "bananas"
    11 "grapes" "oranges"
    21 "pears" "melons"

```

FieldA/B/C are all top-level fields in my data. Now, in the filter section of my LS config file, I want to do this:

```
  if [FieldA] > 10 {
    mutate {
      add_field => { "FaveStat" => [FieldB] }
    }
  else {
    mutate {
      add_field => { "FaveStat" => [FieldC] }
    }
  }

```

I want this:

```
FieldA FieldB FieldC FaveStat
===========================================
     6 "apples" "bananas" "apples"
    11 "grapes" "oranges" "oranges"
    21 "pears" "melons" "melons"

```

Instead, the above syntax is giving me this:

```
FieldA FieldB FieldC FaveStat
===========================================
     6 "apples" "bananas" "FieldB"
    11 "grapes" "oranges" "FieldC"
    21 "pears" "melons" "FieldC"

```

[This](https://www.elastic.co/guide/en/logstash/current/field-references-deepdive.html) suggests that to retrieve the _ **value** _ of a field, you should use brackets. ( `[FieldA]` ) Am I doing something wrong? Thanks!

---

<div class="post-metadata">

**Author:** ![Badger](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/badger/32/25190_2.png) [@Badger](https://discuss.elastic.co/u/Badger)\
**Post date:** [November 15, 2019, 9:05pm UTC](https://discuss.elastic.co/t/logstash-syntax-putting-the-value-of-one-field-into-another/208128/2 "2019-11-15T21:05:20Z")

</div>

> [@redapplesonly](#):
>
> add\_field =\> { "FaveStat" =\> [FieldB] }

Use a sprintf reference to get the value of a field

```
add_field => { "FaveStat" => "%{[FieldB]}" }

```

---

<div class="post-metadata">

**Author:** ![redapplesonly](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/redapplesonly/32/57700_2.png) [@redapplesonly](https://discuss.elastic.co/u/redapplesonly)\
**Post date:** [November 16, 2019, 4:32am UTC](https://discuss.elastic.co/t/logstash-syntax-putting-the-value-of-one-field-into-another/208128/3 "2019-11-16T04:32:31Z")

</div>

> [@Badger](#):
>
> "%{[FieldB]}"

Yes! Brillant! Thank you, that worked perfectly! Badger, you've saved me again. Much appreciated... 🙂

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<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:** [December 14, 2019, 4:32am UTC](https://discuss.elastic.co/t/logstash-syntax-putting-the-value-of-one-field-into-another/208128/4 "2019-12-14T04:32:42Z")

</div>

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