# Environment variable in Logstash **URL:** \ **Category:** Logstash\ **Created:** [December 22, 2017, 10:12am UTC](https://discuss.elastic.co/t/environment-variable-in-logstash/112978 "2017-12-22T10:12:58Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![guyboertje](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/guyboertje/32/31592_2.png) [@guyboertje](https://discuss.elastic.co/u/guyboertje)\ **Post date:** [December 22, 2017, 12:57pm UTC](https://discuss.elastic.co/t/environment-variable-in-logstash/112978/2 "2017-12-22T12:57:58Z")
I suggest that you look into a persisted value. I presume you have two pipelines 1) ActiveMQ via jms input and 2) Kafka via kafka input. Possible Recipe 1. Add a constant field and value to the both pipeline inputs, say "kafka-vn" =\> "kvn". 2. Create a csv file, say `/tmp/logstash-kafka/kafka-version.csv` with the following contents `kvn, 0`. 3. In the kafka pipeline add a translate filter that reads the csv file from above. Use a low refresh interval, 1 second perhaps. `destination` is "old-kvn"; `field` is "kafka-vn". You should now have a field called old-kvn that hold the value read from the file. 4. In the kafka pipeline, add a conditional section in the output section that test whether the `old-kvn` value is different from the value of the field that hold the latest kafka version number. 5. In the above conditional section, use the exec output to echo the latest version number to the file above in the same format `kvn, `. Read [the exec docs](https://www.elastic.co/guide/en/logstash/current/plugins-outputs-exec.html#_description_57). 6. You should be able to see this file change if you run the kafka pipeline on its own. 7. In the activemq pipeline add the same translate filter but this time set the destination to `current-kvn` 8 Use this new field `current-kvn` to set the index in the ES output. If the 1 second latency is too high then, after you get this working, you could try using the `jdbc_streaming` filter (with caching turned off) to do the lookup from a local file based sqlite db. Updating the db will need exec output still. See [https://stackoverflow.com/q/29044340/5349531](https://stackoverflow.com/q/29044340/5349531) This solution will work across restarts. --- _[View the full topic](https://discuss.elastic.co/t/environment-variable-in-logstash/112978)._