storing json output in bash from cloudfromation - json

Question

I am using aws ecs query to get list of properties being used by the current running task.
command -
cft = "aws ecs describe-tasks --cluster arn:aws:ecs:us-west-2:4984314772:cluster/secrets --tasks arn:aws:ecs:us-west-2:4984314772:task/secrets/86855757eec4487f9d4475a1f7c4cb0b
I am storing this in an output variable
output= $( eval $cft)
Output:
"tasks": [
{
"attachments": [
{
"id": "da8a1312-8278-46d5-8e3b-6b6a1d96f820",
"type": "ElasticNetworkInterface",
"status": "ATTACHED",
"details": [
{
"name": "subnetId",
"value": "subnet-0a151f2eb959ad4"
},
{
"name": "networkInterfaceId",
"value": "eni-081948e3666253f"
},
{
"name": "macAddress",
"value": "02:2a:9i:5c:4a:77"
},
{
"name": "privateDnsName",
"value": "ip-172-56-17-177.us-west-2.compute.internal"
},
{
"name": "privateIPv4Address",
"value": "172.56.17.177"
}
]
}
],
"availabilityZone": "us-west-2a",
"clusterArn": "arn:aws:ecs:us-west-2:4984314772:cluster/secrets",
"containers": [
{
"taskArn": "arn:aws:ecs:us-west-2:4984314772:task/secrets/86855757eec4487f9d4475a1f7c4cb0b",
"name": "nginx",
"image": "nginx",
"lastStatus": "PENDING",
"networkInterfaces": [
{
"attachmentId": "da8a1312-8278-46d5-6b6a1d96f820",
"privateIpv4Address": "172.31.17.176"
}
],
"healthStatus": "UNKNOWN",
"cpu": "0"
}
],
"cpu": "256",
"createdAt": "2020-12-10T18:00:16.320000+05:30",
"desiredStatus": "RUNNING",
"group": "family:nginx",
"healthStatus": "UNKNOWN",
"lastStatus": "PENDING",
"launchType": "FARGATE",
"memory": "512",
"overrides": {
"containerOverrides": [
{
"name": "nginx"
}
],
"inferenceAcceleratorOverrides": []
},
"platformVersion": "1.4.0",
"tags": [],
"taskArn": "arn:aws:ecs:us-west-2:4984314772:task/secrets/86855757eec4487f9d4475a1f7c4cb0b",
"taskDefinitionArn": "arn:aws:ecs:us-west-2:4984314772:task-definition/nginx:17",
"version": 2
}
],
"failures": []
}
now if do an echo of $output.tasks[0].containers[0] nothing happens it prints the entire thing again, i want to store the result in output variable and refer different parameter like we do in json format.

Answer 1

You will need to use a json parser such as jq and so:
eval $cft | jq '.tasks[].containers[]'
To avoid using eval you could simple pipe the aws command into jq and so:
aws ecs describe-tasks --cluster arn:aws:ecs:us-west-2:4984314772:cluster/secrets --tasks arn:aws:ecs:us-west-2:4984314772:task/secrets/86855757eec4487f9d4475a1f7c4cb0b | jq '.tasks[].containers[]'
or:
cft=$(aws ecs describe-tasks --cluster arn:aws:ecs:us-west-2:4984314772:cluster/secrets --tasks arn:aws:ecs:us-west-2:4984314772:task/secrets/86855757eec4487f9d4475a1f7c4cb0b | jq '.tasks[].containers[]')
echo $cft | jq '.tasks[].containers[]'