Stopping task on AWS ECS via CLI (program output as argument input bash)

Maybe that helps someone:

Killing task with unique task definition name:

OLD_TASK_ID=$(aws ecs list-tasks --cluster ${ecsClusterName} --desired-status RUNNING --family ${nameTaskDefinition} | egrep "task/" | sed -E "s/.*task\/(.*)\"/\1/")
aws ecs stop-task --cluster ${ecsClusterName} --task ${OLD_TASK_ID}

Killing multiple tasks (same task definition name but different task ids):

OLD_TASK_IDS=$(aws ecs list-tasks --cluster ${ecsClusterName} --desired-status RUNNING --family ${nameTaskDefinition} | egrep "task/" | sed -E "s/.*task\/(.*)\"/\1/" | sed -z 's/\n/ /g')
IFS=', ' read -r -a array <<< "$OLD_TASK_IDS"
for element in "${array[@]}"
do
    aws ecs stop-task --cluster ${ecsClusterName} --task ${element}
done

AWS cli essentially has jq built in so a better (simpler) way to query your task arn would be with:

aws ecs list-tasks --cluster "my-cluster" --service "my-service" --output text --query taskArns[0]