Extracting some fields from an AWS JSON using Powershell - json

Question

Now that Powershell is Open Source and cross platform (with Powershell Core), I thought I'd give it a try again.
I had used in the past and at some point had figured how pipelines work, but it's not super intuitive. It should be, but it isn't, so I'm somewhat stuck...
Task at hand: parse and print several fields from the JSON output of a command. I could probably do it the old fashioned way, with external commands and string processing, à la bash, but I want to learn how to do it the Powershell way™.
And to clarify, I want to do it interactively, in a pipeline. I don't want to write a script, I want to learn how to do this kind of processing in a one-liner (or 2, at most, but basically with Powershell working as a REPL, not as a script tool).
Bash command:
aws cloudformation describe-stack-events --stack-name some-stack-here | jq ".StackEvents[] | [.Timestamp, .ResourceStatus, .ResourceType, .ResourceStatusReason] | join(\" \")"
What this does is take the input JSON and print just 3 fields I'm interested in.
Input JSON:
{
"StackEvents": [
{
"StackId": "arn:aws:cloudformation:some-region-here:some-number-here:stack/some-stack-here/some-id-here",
"EventId": "some-event-id-here",
"ResourceStatus": "UPDATE_COMPLETE",
"ResourceType": "AWS::CloudFormation::Stack",
"Timestamp": "some-date-here",
"StackName": "some-stack-here",
"PhysicalResourceId": "arn:aws:cloudformation:some-region-here:some-number-here:stack/some-stack-here/some-id-here",
"LogicalResourceId": "some-stack-here"
},
{
"StackId": "arn:aws:cloudformation:some-region-here:some-number-here:stack/some-stack-here/some-id-here",
"EventId": "some-event-id-here",
"ResourceStatus": "UPDATE_COMPLETE_CLEANUP_IN_PROGRESS",
"ResourceType": "AWS::CloudFormation::Stack",
"Timestamp": "some-date-here",
"StackName": "some-stack-here",
"PhysicalResourceId": "arn:aws:cloudformation:some-region-here:some-number-here:stack/some-stack-here/some-id-here",
"LogicalResourceId": "some-stack-here"
}
]
}
Command output:
"some-date-here UPDATE_COMPLETE AWS::CloudFormation::Stack "
"some-date-here UPDATE_COMPLETE_CLEANUP_IN_PROGRESS AWS::CloudFormation::Stack "
(I think this should be on Stackoverflow because the topic involves a pretty solid understanding of Powershell concepts, including .NET objects, much closer to programming than to sysadmining, i.e. SuperUser or so.)

Answer 1

You can do:
$j = aws cloudformation describe-stack-events --stack-name some-stack-here | ConvertFrom-Json
$j.StackEvents | % { "{0} {1} {2}" -f $_.Timestamp, $_.Resourcestatus, $_.ResourceType }
Use the ConvertFrom-Json cmdlet to store the command result into a powershell object, then you can select the StackEvents array and loop it to select the required values.
If you wanted to do it in one line:
(aws cloudformation describe-stack-events --stack-name some-stack-here | ConvertFrom-Json).StackEvents | %
{ "{0} {1} {2}" -f $_.Timestamp, $_.Resourcestatus, $_.ResourceType }