ConvertTo-JSON from string - access JSON fields by name in PowerShell

Question

How can I access a field like $body.uuid? This is what I have tried:

$body = @"
{   "uuid": "Test07",
    "subject": "Template07-Subject",
}
"@

$bodyJSON = ConvertTo-Json $body

Write-Host $bodyJSON
Write-Host "uuid=$($bodyJSON.uuid)" 
Write-Host "uuid=$($bodyJSON.$uuid)"

Results:

"{   \"uuid\": \"Test07\",\r\n    \"subject\": \"Template07-Subject\",\r\n}"
uuid=
uuid=

The string already contains json - you want $object = ConvertFrom-Json $body; $object.uuid — Mathias R. Jessen
– Mathias R. Jessen, Commented Oct 8, 2021 at 21:19
@MathiasR.Jessen I tried ConverFrom-JSON and it gave: ConvertFrom-Json : Invalid JSON primitive: — NealWalters
– NealWalters, Commented Oct 8, 2021 at 21:45

mklement0 · Accepted Answer · 2021-10-09 07:20:05Z

3

Your $body variable contains a JSON string.
- Unless your intent is to embed that string in another JSON string, do not call ConvertTo-Json on it - the latter's purpose is to convert objects to JSON strings.
In order to parse the JSON string into an object (graph), pass it to ConvertFrom-Json, which returns [pscustomobject] instance(s).
- You can use regular property access, such as .uuid on the resulting object(s).

Note:

As bluuf points out, your original JSON contains an extraneous , after the "subject" property, which makes it technically malformed - this has been corrected below.
Note, however, that ConvertTo-Json in PowerShell (Core) 7+ still accepts such JSON, whereas Windows PowerShell does not.

# Create a string containing JSON
$body = @"
{   
    "uuid": "Test07",
    "subject": "Template07-Subject"
}
"@

# Parse the JSON string into a PowerShell object (graph).
$bodyAsObject = ConvertFrom-Json $body

# Now you can use property access.
$bodyAsObject.uuid  # -> 'Test07'

edited Oct 9, 2021 at 7:20

answered Oct 8, 2021 at 22:07

mklement0

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2 Comments

NealWalters Over a year ago

Thanks for the good explanation. The comma was there because I delete a bunch of other fields to create a smaller test case, and forgot about it. I didn't catch that was the reason for the error with ConvertFrom-Json. So bottom line, PowerShell doesn't have a JSON object concept then. Instead it uses pscustomobject to simulate that?

mklement0 Over a year ago

@NealWalters, yes, it's easy to forget a trailing comma, which is why some JSON parsers conveniently ignore it. To PowerShell, JSON is just a string - a text-based serialization format that must be deserialized into a language-specific object graph (including in JavaScript with JSON.parse()). In PowerShell, you use ConvertFrom-Json, which returns an [array of] [nested] [pscustomobject] instance(s).

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