Minh Vu
Software Engineer
Hi 👋, I'm a software engineer (backend, applied AI, Elastic Stack). My blog shares practical tutorials, mostly on the Elastic Stack and Next.js. LeetCode 1756 (top 10.4% globally, Sep 2026). Actively seeking SDE roles — let's get in touch!
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Conditional filtering is a very important feature that helps you to process data based on different conditions.
This tutorial, will show you how to use conditional filtering in Logstash with the if/else statement.
To filter data conditionally in Logstash, you can use the if/else statement: if <condition> { ... } else { ... }.
The syntax is:
if <condition> { # do something } else if <condition> { # do something else } else { # do something else }
For example, to check if the field [event][duration] is greater than 1000, you can use the following code:
if [event][duration] > 1000 { # do something } else { # do something else }
To check if a field exists in Logstash, you can use if [field], which will return true if the field exists, and false if the field does not exist.
For example, to check if the field [user][name] exists, you can use the following code:
if [user][name] { # do something } else { # do something else }
Similarly, to check if a field is empty in Logstash, you can use if [field] == "", which will return true if the field is empty, and false if the field is not empty.
For example, to check if the field [user][age] is missing, you can use the following code:
if [user][age] == "" { # do something } else { # do something else }
To check if a field is null in Logstash, you can use if [field] == nil, which will return true if the field is null, and false if the field is not null.
For example, to check if the field [user][email] is null, you can use the following code:
if [user][email] == nil { # do something } else { # do something else }
To check if a field starts with a string in Logstash, you can use if [field] =~ /^<string>/, which will return true if the field starts with the string, and false if the field does not start with the string.
For example, to check if the field [user][name] starts with the string Minh, you can use the following code:
if [user][name] =~ /^Minh/ { # do something } else { # do something else }
In this tutorial, we learned how to use conditional filtering in Logstash with the if/else statement.
There are some common cases that need the help of conditional filtering, such as:
if [field]if [field] == ""if [field] == nilif [field] =~ /^<string>/I hope this helps and see you in the next tutorial!
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Comments
findhi
Apr 02, 2024
Nice work, keep it up