Adding a key-value pair to a JSON object in Powershell without using ConvertFrom-Json

Question

Is there a way to add a key-value pair to a JSON object in Powershell without using the ConvertFrom-Json cmdlet? The script I currently have outputs a JSON file that is unreadable because it has several parent objects, but I want to merge all of the parent objects into one. However, I am unsure how to do that since, I have tried creating one parent object to use for all functions, but I receive an error when I try to convert the JSON object to a PSObject.

Here is a piece of my JSON file:

{
  "HostName": "MMuns-L2314"
}
{
  "SerialNumber": "BNW35Y3"
}
{
  "LatestUptime": "2025-06-10T11:54:17.5000000-04:00"
}

but I want it to look like this:

{
  "HostName" : "MMuns-L2314",
  "SerialNumber" : "BNW35Y3",
  "LatestUptime" : "2025-06-10T11:54:17.5000000-04:00"
}

Additionally, here are the functions I have initially used that pulls and then adds the information to JSON:

Function Get-Hostname { 
  $hostname = hostname
  $hostObj = @{
    HostName = $hostname
  }
  $hostJSON = $hostObj | ConvertTo-Json
  $hostJSON | Out-File -FilePath "$HOME/Downloads/serverscript.json"


}

Function Get-SerialNumber { 
  $SerialNumber = (Get-CimInstance Win32_BIOS).SerialNumber
  $serialObj = @{
    SerialNumber = $SerialNumber
  }
  $serialJSON = $serialObj | ConvertTo-Json
  Add-Content -Path "$HOME\Downloads\serverscript.json" -Value $serialJSON
}

Function Get-Upt { 
  $upt = (Get-CimInstance Win32_OperatingSystem).LastBootUpTime.ToString('o')
  $uptObj = @{
    LatestUptime = $upt
  }
  $uptJSON = $uptObj | ConvertTo-Json
  Add-Content -Path "$HOME\Downloads\serverscript.json" -Value $uptJSON
}

Finally, when I pipe a json object (i.e. '$hostJson') to the ConvertFrom-Json cmdlet, I get a null output and an error telling me that I am "unable to bind" the output to a variable:

ConvertFrom-Json : Cannot bind argument to parameter 'InputObject' because it is null.
At line:24 char:25
+   $hostJSON = $hostJSON | ConvertFrom-Json

The code referenced in the error message ($hostJSON = $hostJSON | ConvertFrom-Json) is nowhere to be found in the sample code you posted above. Please make sure the code you've posted is the actual code you're troubleshooting — Mathias R. Jessen
– Mathias R. Jessen, Commented Jun 16 at 14:37
@MathiasR.Jessen I included the error message to show that if I were to add that line of code, I would receive an error. Also, I never said that when I run the initial code sample, I receive an error. I said that, when I pipe the object to ConvertFrom-Json (as a seperate line), I receive an error, which is why I am searching for an alternative method for the main issue I have of appending to a JSON object. — mimi m
– mimi m, Commented Jun 16 at 14:47

mklement0 · Accepted Answer · 2025-06-16 18:34:37Z

4

1 PowerShell object/hashtable = 1 JSON object.

In other words, if you want a JSON document consisting of a single object with those 3 properties, then you'll want to create exactly one object in PowerShell and then convert that to JSON at once:

$wholeObject = [ordered]@{
  HostName = hostname
  SerialNumber = (Get-CimInstance Win32_BIOS).SerialNumber
  LatestUptime = (Get-CimInstance Win32_OperatingSystem).LastBootUpTime.ToString('o')
}

# this will now produce the expected output
$wholeObject |ConvertTo-Json

edited Jun 16 at 18:34

mklement0

453k68 gold badges729 silver badges989 bronze badges

answered Jun 16 at 14:48

Mathias R. Jessen

178k13 gold badges175 silver badges234 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

mimi m Jun 16 at 16:12

Were you able to figure out why I receive an error message when I try to use ConvertFrom-Json?

mklement0 Jun 16 at 18:37

@mimim: The error message implies that $hostJSON is $null. Note that your functions, despite being named Get-*, don't output (return) anything (and that the function-local $hostJSON variable you define isn't seen by the caller).

Collectives™ on Stack Overflow

Adding a key-value pair to a JSON object in Powershell without using ConvertFrom-Json

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related