# export the task def
family='TaskDefName'
$ aws ecs describe-task-definition --task-definition $family \
--query "taskDefinition.{family:family, taskRoleArn:taskRoleArn, executionRoleArn:executionRoleArn, networkMode:networkMode, containerDefinitions:containerDefinitions, volumes:volumes, placementConstraints:placementConstraints, requiresCompatibilities:requiresCompatibilities, cpu:cpu, memory:memory, tags:tags, pidMode:pidMode, ipcMode:ipcMode, proxyConfiguration:proxyConfiguration}" | jq 'del(.[] | nulls)' > taskDef.json

# import the task def into newFamily task family
$ aws ecs register-task-definition --cli-input-json file://taskDef.json --family newFamily

# one-liner
aws ecs describe-task-definition --task-definition $family \
--query "taskDefinition.{family:family, taskRoleArn:taskRoleArn, executionRoleArn:executionRoleArn, networkMode:networkMode, containerDefinitions:containerDefinitions, volumes:volumes, placementConstraints:placementConstraints, requiresCompatibilities:requiresCompatibilities, cpu:cpu, memory:memory, tags:tags, pidMode:pidMode, ipcMode:ipcMode, proxyConfiguration:proxyConfiguration}" | jq 'del(.[] | nulls)' | xargs -0 aws ecs register-task-definition --family newFamily --cli-input-json

# convert the taskDef.json to taskDef.yaml
docker run -v ${PWD}:/workdir mikefarah/yq yq r taskDef.json > taskDef.yaml