# Parsing lines that only match a start string
**URL:** https://discuss.elastic.co/t/parsing-lines-that-only-match-a-start-string/215125
**Category:** Logstash
**Created:** [January 15, 2020, 11:38am UTC](https://discuss.elastic.co/t/parsing-lines-that-only-match-a-start-string/215125 "2020-01-15T11:38:23Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@whoatemyjam](https://discuss.elastic.co/u/whoatemyjam)
#### Post date: [January 15, 2020, 11:38am UTC](https://discuss.elastic.co/t/parsing-lines-that-only-match-a-start-string/215125/1 "2020-01-15T11:38:23Z")
hi
Please if you can help.
How can we get logstash to log only the lines starting with "central-logging": "true" and ignore rest which we dont need.
{ "central-logging": "true", "log-date": "2020-01-15 11:19:08 UTC", "severity": "INFO", "BuildSetID": "sim-12345678", "Process": "CheckJobInputs", "log-message": "Directory: /images exists"}
---
### Author:  [@andres-perez](https://discuss.elastic.co/u/andres-perez)
#### Post date: [January 15, 2020, 2:08pm UTC](https://discuss.elastic.co/t/parsing-lines-that-only-match-a-start-string/215125/2 "2020-01-15T14:08:18Z")
> [@whoatemyjam](#):
>
> log only the lines starting with "central-logging": "true" and ignore rest
If by ignore you mean "discard all other events and not even index them", you can start your filter with a condition to `drop` the messages that won't match a regexp `!~` looking for log contents that start with `^` your desired string. The curly bracket must be escaped `\{`.
That is:
```
if [message] !~ /^\{ "central-logging": "true"/ {
drop { }
}
```
Having said that, if you may want to process the other lines in the future, it may be worth taking a look at the [json filter](https://www.elastic.co/guide/en/logstash/current/plugins-filters-json.html) and set conditions depending on the existence or value of "central-logging".
---
### Author:  [@whoatemyjam](https://discuss.elastic.co/u/whoatemyjam)
#### Post date: [January 21, 2020, 3:11pm UTC](https://discuss.elastic.co/t/parsing-lines-that-only-match-a-start-string/215125/3 "2020-01-21T15:11:41Z")
Hi Andres
I have a huge log and i just want to print the line that matches with { "central-logging": "true", withing the message
Thanks
---
### Author:  [@andres-perez](https://discuss.elastic.co/u/andres-perez)
#### Post date: [January 27, 2020, 9:57am UTC](https://discuss.elastic.co/t/parsing-lines-that-only-match-a-start-string/215125/4 "2020-01-27T09:57:59Z")
So, either you discard all the other messages (as I have described in my previous comment) or you add a condition in the output section to log only the messages that match `=~` your string.
You can see examples in the documentation: [https://www.elastic.co/guide/en/logstash/current/event-dependent-configuration.html#conditionals](https://www.elastic.co/guide/en/logstash/current/event-dependent-configuration.html#conditionals)
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [February 24, 2020, 9:58am UTC](https://discuss.elastic.co/t/parsing-lines-that-only-match-a-start-string/215125/5 "2020-02-24T09:58:04Z")
This topic was automatically closed 28 days after the last reply. New replies are no longer allowed.