# Extracting a substring

**URL:** https://discuss.elastic.co/t/extracting-a-substring/134268
**Category:** Logstash
**Created:** [June 1, 2018, 8:03pm UTC](https://discuss.elastic.co/t/extracting-a-substring/134268 "2018-06-01T20:03:32Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![sandeepnarla22322](https://avatars.discourse-cdn.com/v4/letter/s/57b2e6/32.png) [@sandeepnarla22322](https://discuss.elastic.co/u/sandeepnarla22322)
#### Post date: [June 1, 2018, 8:03pm UTC](https://discuss.elastic.co/t/extracting-a-substring/134268/1 "2018-06-01T20:03:32Z")

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I was wondering what I can use to extract the first three letters of a given string

"/opt/LogStashOutputFormatted/TMOES/TNTMO072.2018-05-02\_08:40.log"

I want to extract " TNT" from the string was able to extract TNTMO072 this using the dissect filter

dissect {  
mapping =\> {  
"path" =\> "/%{folder1}/%{folder2}/%{folder3}/%{TmoesNodename}.%{LogName}"  
}  
}

any suggestestions would be great

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<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: [June 1, 2018, 10:28pm UTC](https://discuss.elastic.co/t/extracting-a-substring/134268/2 "2018-06-01T22:28:12Z")

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I would do it using grok.

```
grok { match => ["fieldContainingTNTMO072", "^(?<threeLetters>...)"] }
```

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<div class="post-metadata">

### Author: ![sandeepnarla22322](https://avatars.discourse-cdn.com/v4/letter/s/57b2e6/32.png) [@sandeepnarla22322](https://discuss.elastic.co/u/sandeepnarla22322)
#### Post date: [June 4, 2018, 3:59pm UTC](https://discuss.elastic.co/t/extracting-a-substring/134268/3 "2018-06-04T15:59:05Z")

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thanks @Badger

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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: [July 2, 2018, 3:59pm UTC](https://discuss.elastic.co/t/extracting-a-substring/134268/4 "2018-07-02T15:59:11Z")

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