AWS CLI, using `--cli-input-json` in a pipeline

I'd like to use the aws command line application in a pipeline, but it doesn't appear to be possible.

A working example is:

$ aws ecs register-task-definition --cli-input-json file://./mytask.json 

However the following do not work:

$ cat ./mytask.json \ | aws ecs register-task-definition --cli-input-json file:///dev/stdin Error parsing parameter 'cli-input-json': Invalid JSON: Expecting value: line 1 column 1 (char 0) JSON received: 

$ aws ecs register-task-definition --cli-input-json file://<(cat ./mytask.json) Error parsing parameter 'cli-input-json': Invalid JSON: Expecting value: line 1 column 1 (char 0) JSON received: 

3 Answers

Found a workaround for the time being with xargs that is quite clean:

cat ./mytask.json \ | xargs -0 aws ecs register-task-definition --cli-input-json 

It only adds xargs -0 and requires --cli-input-json to be the last argument

I went digging... It looks like aws will read the indicated file twice, using the second dataset for it's operation. Of course, in a pipeline, the second read() will get nothing.

I've added a pipe:// prefix/schema (commit) for use in this situation which will cache the value... I've also made a pull request.

I was able to pass the JSON as a variable on --cli-input-json and inject bash variables too.

So your example should be:

aws ecs register-task-definition --cli-input-json "$(cat < ./mytask.json)" 

In my scenario at hand I have:

1. Either pass a JSON as you would like

   aws autoscaling start-instance-refresh --cli-input-json "$(cat < ./options.json )"

2. Or as HEREDOC in order to pass other variables too. (Not requested but may be useful)

asg_nominal_name=AutoScalingGroupName aws autoscaling start-instance-refresh --cli-input-json "$(cat <<JSON { "AutoScalingGroupName": "${asg_nominal_name}", "Preferences": { "InstanceWarmup": 300, "MinHealthyPercentage": 100 } } JSON )" 

I am not so familiar to explain the why in bash terms. Feel free.