How to filter an array of JSON objects with jq?

Question

I have the following JSON input:

{   "zk_kafka": [     {       "InstanceType": "t2.medium",       "zkMemory": "16",       "kafkaMemory": "8"     },     {       "InstanceType": "t2.small",       "zkMemory": "8",       "kafkaMemory": "4"     }   ],   "es_hdfs": [     {       "InstanceType": "t2.medium",       "esMemory": "16",       "hdfsMemory": "8"     },     {       "InstanceType": "t2.small",       "esMemory": "8",       "hdfsMemory": "4"     }   ] } 

First I want to select an array by a property name. And then I want to select an object of the array by the value of the property InstanceType.

Example for the property zk_kafka and the value t2.medium:

{   "InstanceType": "t2.medium",   "zkMemory": "16",   "kafkaMemory": "8" } 

I know how to select the array:

jq .zk_kafka 

But I do not know how to filter the array of object by a property value.

Answer 1

Use the select filter of jq:

jq '.zk_kafka | .[] | select(.InstanceType == "t2.medium")' 

Use the --arg option to pass an argument to the query to avoid injections.

jq --arg instance "t2.medium" '.zk_kafka | .[] | select(.InstanceType == $instance)' 

jq has a manual, a tutorial and a cookbook.