# Need clarity - logstash 'filter' patterns

**URL:** <https://discuss.elastic.co/t/need-clarity-logstash-filter-patterns/113207>\
**Category:** Logstash\
**Created:** [December 26, 2017, 12:09pm UTC](https://discuss.elastic.co/t/need-clarity-logstash-filter-patterns/113207 "2017-12-26T12:09:28Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![subin](https://avatars.discourse-cdn.com/v4/letter/s/58956e/32.png) [@subin](https://discuss.elastic.co/u/subin)\
**Post date:** [December 26, 2017, 12:09pm UTC](https://discuss.elastic.co/t/need-clarity-logstash-filter-patterns/113207/1 "2017-12-26T12:09:28Z")

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In the docs and various examples, I'm seeing `if` statements in Input section, like:

> if [message] =~ /dovecot: (imap|pop3|managesieve)-login

Apart from `[message]`, what other fields can `if` take? I don't have much understanding about this. Is any documentation available?

Thanks.

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**Author:** ![arisbanach](https://avatars.discourse-cdn.com/v4/letter/a/f07891/32.png) [@arisbanach](https://discuss.elastic.co/u/arisbanach)\
**Post date:** [December 27, 2017, 12:53am UTC](https://discuss.elastic.co/t/need-clarity-logstash-filter-patterns/113207/2 "2017-12-27T00:53:00Z")

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[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)

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**Author:** ![warkolm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/warkolm/32/39224_2.png) [@warkolm](https://discuss.elastic.co/u/warkolm)\
**Post date:** [December 27, 2017, 2:23am UTC](https://discuss.elastic.co/t/need-clarity-logstash-filter-patterns/113207/3 "2017-12-27T02:23:33Z")

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Basically you can put a reference to a field, or a value.

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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:** [January 24, 2018, 2:23am UTC](https://discuss.elastic.co/t/need-clarity-logstash-filter-patterns/113207/4 "2018-01-24T02:23:35Z")

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