AWS Step function use input value to make complete command - amazon-web-services

Question

How can use input in my state machine in mid of a string?
For example, I want to make a command using input params like this
["python test.py", "--name=$.name", "--age=$.age"]
But as per AWS documentation, I can't pass like above. I can only pass like
{"Command.$": "$.age"}
Why this strange structure is required. Why do I need to use .$ in the key. Why can't I use $.age freely anywhere?
What I want to achieve is something like this.
{
"Comment": "A description of my state machine",
"StartAt": "Pipeline",
"States": {
"Run Pipeline": {
"Type": "Task",
"Resource": "arn:aws:states:::ecs:runTask.sync",
"Parameters": {
"LaunchType": "FARGATE",
"Cluster": "aaaaaaaaaaaaaa",
"TaskDefinition": "aaaaaaaaaaaaaa",
"Overrides": {
"ContainerOverrides": [{
"Name": "my_container",
"Command": [
"python test.py",
"--name=$.name",
"--age=$.age"
]
}]
}
},
"End": true
}
}
}
where my step function input is
{"name": "Rahul", "age": 25}

Answer 1

The .$ tells step-functions that you are passing a path and not a literal string value.
Input/Ouput Path Params Doc
If you want to construct a string from inputs, you should be able to use intrinsic string formatting:
States.Format('python test.py --name={} --age={}', $.name, $.age)
Intrinsic Function Doc
{
"Comment": "A description of my state machine",
"StartAt": "Run Pipeline",
"States": {
"Run Pipeline": {
"Type": "Task",
"Resource": "arn:aws:states:::ecs:runTask.sync",
"Parameters": {
"LaunchType": "FARGATE",
"Cluster": "aaaaaaaaaaaaaa",
"TaskDefinition": "aaaaaaaaaaaaaa",
"Overrides": {
"ContainerOverrides": [{
"Name": "my_container",
"Command.$": "States.Array(States.Format('python test.py --name={} --age={}', $.name, $.age))"
}]
}
},
"End": true
}
}
}
States.Array makes an array out of a list of inputs.
States.Format lets you construct a string using literal and interpolated (variable) inputs.