Add values inside foreach powershell

Question

I have the following code:

foreach ($region in (Get-AWSRegion)) {
    $images = aws ec2 describe-instances --output text --query 'Reservations[*].Instances[*].[ImageId]' | sort | uniq -c
}

$images

Above code gives me something like:

3 ami-123**

But I am trying to get all AMI's inside all regions together so it should be something like:

9 ami-123**

When I try something like:

$images += aws ec2 describe-instances --output text --query 'Reservations[*].Instances[*].[ImageId]' | sort | uniq -c

I get: 3 ami-123** 3 ami-123** 3 ami-123**

Is there a way to do this?

While you iterate Regions your aws command doesn't take the currently iterated Region into account, so why do you do this 1st place? — user6811411
– user6811411, Commented Aug 8, 2019 at 14:36
LotPings - So how can I change this? I am basically trying to get all unique ami's in all regions and run an operation on that. My thought was if I get all unique ami's from all regions then it is less overhead to run a query on each ami. — NoviceMe
– NoviceMe, Commented Aug 8, 2019 at 14:40

Mathias R. Jessen · Accepted Answer · 2019-08-08 14:40:42Z

3

Three immediate problems - first, you keep overwriting the value of $images inside the loop, and as you've found you can solve that by adding to the previous result set.

Second problem is that you're not actually targeting the $region, so you keep getting the same result from the default region configured for aws - specify --region $region inside the loop (assuming that Get-AWSRegion returns the region identifier as a string).

Third problem is a bit more... fundamental - the aws cli returns a string, so you'll need to manually parse that and aggregate the results - you could do so with a [hashtable] and a simple regex pattern:

# Create hashtable to aggregate results
$ImageIDCounts = @{}

foreach($region in Get-AWSRegion){
    $perRegionCount = aws ec2 describe-instances --region $region --output text --query 'Reservations[*].Instances[*].[ImageId]' | sort | uniq -c
    foreach($entry in $perRegionCount){
        if($entry -match '^\s*(\d+)\s+(.*)$'){
            $Count = $Matches[1] -as [int]
            $ImageID = $Matches[2].Trim()

            $ImageIDCounts[$ImageID] += $Count 
        }
    }
}

$ImageIDCounts now contains one entry per unique ImageID, so you can do:

$ami123count = $ImageIDCounts['ami-123']

answered Aug 8, 2019 at 14:40

Mathias R. Jessen

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4 Comments

NoviceMe Over a year ago

Awesome thank you! I was not looking for count though only unique image id's. I will try to get that from above solution.

user6811411 Over a year ago

I've no clue, but I guess there are other options for --output, not just text ;-) Reading the docs could help AWS Command Line Interface - User Guide

Mathias R. Jessen Over a year ago

@NoviceMe That's as easy as just grabbing the hashtable keys: $UniqueImageIDs = $ImageIDCounts.Keys

Mathias R. Jessen Over a year ago

@LotPings indeed, although you'll still need to do some level of post-processing on the output (ConvertFrom-JSON, XmlDocument.Load() etc.) - aws is an external executable so the output is always strings :)

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