Getting Dynamic Key value from json using Powershell

Question

The end goal here is to get the x64.msi download link based on the latest version of the Nessus Agent. I need a way to get the first Key with "Nessus Agent" string match and then iterate all objects below until a match is found for the value in the file parameter.

Note, the ""Nessus Agents - 8.2.4" is dynamic as the version number will change over time so this key value cannot be hard coded.

I am new to Powershell and can't find any examples on how to do this, any help would be great! :)

example JSON object below:

{
   "releases":{
      "latest":{
         "Plugins Archive":[
            {
               "file":"Agent_plugins_expires_2021-05-23.tgz",
               "version":"null",
               "size":585141662,
               "release_date":"05/19/2021",
               "product_release_date":"05/19/2021",
               "md5":"d001d04decd3ddc0689590c24cd70b4f",
               "sha256":"a642b52c428b9ffd7214a76de65a895b2b1b863a9156223e7a80561c1538e766",
               "file_url":"https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/Agent_plugins_expires_latest.tgz"
            }
         ],
         "Nessus Agents - 8.2.4":[
            {
               "file":"NessusAgent-8.2.4-amzn.x86_64.rpm",
               "version":"8.2.4",
               "size":17067122,
               "release_date":"03/31/2021",
               "product_release_date":"04/08/2021",
               "md5":"00f3d1be5355f256621f9b1241cf0c05",
               "sha256":"5c6c3478e35296331e971278eabeaf693c3691f1ebf734adcae3cfbf6c6c23fa",
               "file_url":"https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/NessusAgent-latest-amzn.x86_64.rpm"
            },
            {
               "file":"NessusAgent-8.2.4-debian6_amd64.deb",
               "version":"8.2.4",
               "size":16824112,
               "release_date":"03/31/2021",
               "product_release_date":"04/08/2021",
               "md5":"c888f6e4ab60b4a2bd85f0b291d44171",
               "sha256":"c3655308cb3adbd1319a6eb77210c4eb2c031f5d2288d9affbc103ea0939f220",
               "file_url":"https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/NessusAgent-latest-debian6_amd64.deb"
            },
            {
               "file":"NessusAgent-8.2.4-es5.x86_64.rpm",
               "version":"8.2.4",
               "size":19471101,
               "release_date":"03/31/2021",
               "product_release_date":"04/08/2021",
               "md5":"c72ca4c47b44067204e394c6d131bb7b",
               "sha256":"06f70cf0fbd5d0622367042550d24c48545f61ea7f0856532ae2efa70475a06f",
               "file_url":"https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/NessusAgent-latest-es5.x86_64.rpm"
            },
            {
               "file":"NessusAgent-8.2.4-es6.x86_64.rpm",
               "version":"8.2.4",
               "size":19407452,
               "release_date":"03/31/2021",
               "product_release_date":"04/08/2021",
               "md5":"3b87ee638758201570adf66cbc369b67",
               "sha256":"56e7c130c38d915332093a287cdab39d402777b69f39afd7e1f476423b477af1",
               "file_url":"https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/NessusAgent-latest-es6.x86_64.rpm"
            },
            {
               "file":"nessus-agent-updates-8.2.4.tar.gz",
               "version":"8.2.4",
               "size":590396412,
               "release_date":"03/31/2021",
               "product_release_date":"04/08/2021",
               "md5":"4348bcf458acfb826c447ff8b5176057",
               "sha256":"0130b16ad01d9e189faaf8f51a9ebf824da69977d39b58e50460a24d2dc480a6",
               "file_url":"https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/nessus-agent-updates-latest.tar.gz"
            }

My code starts with:

$output = "C:\nessus_releases.json";
$jout = Get-Content -Path $output -raw | ConvertFrom-Json;

As a test, if I run the following, it does return the second object under the "Nessus-Agents - 8.2.4" key:

Write-Output($jout.releases.latest.'Nessus Agents - 8.2.4'.Item(1));

However, trying things like the below to get the key values, doesn't return anything:

$jout.releases.latest | ForEach-Object {
    Write-Output($_.key);
};

Also tried the below that again, doesn't return anything:

$version = $jout.releases.latest | Where-Object {$_ -match "Nessus Agents"}
Write-Output($version)

UPDATE:

I think I have a way which seems to work to get the key name:

$properties = $jout.releases.latest |
Get-Member -MemberType Properties |
Select-Object -ExpandProperty Name

$version = $properties | Where-Object {$_ -match "Nessus Agents"}

Write-Output($version)

This returns:

Nessus Agents - 8.2.4

@Ash I've tried the following $jout.releases.latest | ForEach-Object { Write-Output($_.key); } also tried: $keys = $jout.releases.keys foreach ($key in $keys) { Write-Output($json[$key]) } but they return nothing. As a test, just doing the following: Write-Output($jout.releases.latest.'Nessus Agents - 8.2.4'.Item(1)) Does return the second agent object. So the data is readable. I just don't know how to get the first key name starting with "Nessus Agents*" — Gerald McNicholl
– Gerald McNicholl, Commented May 20, 2021 at 8:36
Sorry, I should state the above was tried after loading the json file like so: $jout = Get-Content -Path $output | ConvertFrom-Json — Gerald McNicholl
– Gerald McNicholl, Commented May 20, 2021 at 8:48
Please edit you question and put what you have tried in it. It's easier to read in the question. This helps people either add to what you have done so far, or suggest a new approach. It also makes it easier to understand for people who might have the same issue that you are having. — Ash
– Ash, Commented May 20, 2021 at 8:53
sorry @Ash. I have updated the question with the code I have tried. — Gerald McNicholl
– Gerald McNicholl, Commented May 20, 2021 at 9:07

Frenchy · Accepted Answer · 2021-05-20 14:25:39Z

if i have well understood what you want:

$output = "C:\nessus_releases.json"
$jout = Get-Content -Path $output | ConvertFrom-Json

$keys = $jout.releases.latest.PSobject.Properties

foreach($key in $keys)
{
    if($key.Name.StartsWith("Nessus Agents")){
        $objs = $jout.releases.latest.($key.Name)
        "agent " + $key.Name + " : " + $objs.Count + " values"
        foreach($f in $objs){         
            $f.file + " -> url " + $f.file_url
        }
        return
    }
}

result:

agent Nessus Agents - 8.2.4 : 5 values
NessusAgent-8.2.4-amzn.x86_64.rpm -> url https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/NessusAgent-latest-amzn.x86_64.rpm
NessusAgent-8.2.4-debian6_amd64.deb -> url https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/NessusAgent-latest-debian6_amd64.deb
NessusAgent-8.2.4-es5.x86_64.rpm -> url https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/NessusAgent-latest-es5.x86_64.rpm
NessusAgent-8.2.4-es6.x86_64.rpm -> url https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/NessusAgent-latest-es6.x86_64.rpm
nessus-agent-updates-8.2.4.tar.gz -> url https://www.tenable.com/downloads/api/v2/pages/nessus-agents/files/nessus-agent-updates-latest.tar.gz

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