Method and example of result polling - Alibaba Cloud CLI

The return results of specific API operations of Alibaba Cloud services can change over time. You can use the result polling feature to poll return results and return data when a parameter changes to a specific value.

Description of the --waiter option

You can poll return results by using the --waiter option. The following table describes the parameters of this option.

Parameter	Description
expr	The JMESPath expression that specifies the parameter to be polled in the returned JSON data.
to	The expected value of the polled parameter.

Example

Scenario
After you run the command to create an Elastic Compute Service (ECS) instance, you call the DescribeInstances operation to query the details of the instance. After you use the --waiter option, Alibaba Cloud CLI polls the instance status at regular intervals. When the instance is created and started, the instance enters the Running state at which point Alibaba Cloud CLI stops polling results and returns the response of the DescribeInstances operation.
Sample command
Run the following command to poll the instance status until the instance is in the Running state and then return results.
```
aliyun ecs DescribeInstances --InstanceIds '["i-12345678912345678123"]' 
  --waiter expr='Instances.Instance[0].Status' to=Running
```