# Extract a substring and assign to new field
**URL:** https://discuss.elastic.co/t/extract-a-substring-and-assign-to-new-field/284692
**Category:** Logstash
**Created:** [September 21, 2021, 8:37am UTC](https://discuss.elastic.co/t/extract-a-substring-and-assign-to-new-field/284692 "2021-09-21T08:37:33Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Andrea\_Bozzano](https://discuss.elastic.co/u/Andrea_Bozzano)
#### Post date: [September 21, 2021, 8:37am UTC](https://discuss.elastic.co/t/extract-a-substring-and-assign-to-new-field/284692/1 "2021-09-21T08:37:33Z")
Hi everyone!
Hope everyone's good.
in my application, i'm sending a JSON wich has a string field always made of 16 char
For example: XXXYYY12Y00K111H
Is there a fine way, or do you have any particular hint to extract, for example, the number 12, and assign it to a new field?
Thank you for any reply!
---
### Author:  [@Badger](https://discuss.elastic.co/u/Badger)
#### Post date: [September 21, 2021, 2:24pm UTC](https://discuss.elastic.co/t/extract-a-substring-and-assign-to-new-field/284692/2 "2021-09-21T14:24:30Z")
You can use grok
```
grok { match => { "someField" => "^.{6}(?..)" } }
```
will extract the seventh and eighth characters from a string.
---
### Author:  [@Andrea\_Bozzano](https://discuss.elastic.co/u/Andrea_Bozzano)
#### Post date: [September 21, 2021, 3:10pm UTC](https://discuss.elastic.co/t/extract-a-substring-and-assign-to-new-field/284692/3 "2021-09-21T15:10:18Z")
Thanks!
This actually worked quite good, and with some adaptation also for other things 🙂
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [October 19, 2021, 3:10pm UTC](https://discuss.elastic.co/t/extract-a-substring-and-assign-to-new-field/284692/4 "2021-10-19T15:10:48Z")
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