Windows PowerShell parsing json - bracket vs dot

Question

Using Windows PowerShell terminal for running a PS script.

I need to do (among the rest) some json file parsing. I ended up in a strange situation, here below posting a minimal example:

Json file:

{
  "mykey": "myvalue"
}

PS script:

$jsonContent = Get-Content "myfile.json" -Raw | ConvertFrom-Json
$jsonContent.GetType().FullName
$key = "mykey"
Write-Host "Using bracket notation: $($jsonContent[$key])"
Write-Host "Using dot notation: $($jsonContent.$key)"

Output:

System.Management.Automation.PSCustomObject
Using bracket notation:
Using dot notation: myvalue

I expected the exact opposite, bracket notation to work and dot notation to not work: what's happening here?

As an additional detail, $PSVersionTable.PSVersion returns 5.1.22621.4391.

Generally, PowerShell supports only dot notation for accessing instance of types that do not also implement the IDictionary interface (e.g., ([pscustomobject] @{ Foo = 42 }).Foo). For instances of types that do implement the IDictionary interface, such as [hashtable], PowerShell suports index notation and dot notation interchangeably (e.g., @{ Foo = 42 }['Foo'] or @{ Foo = 42 }.Foo). — mklement0
– mklement0, Commented Jun 21 at 19:59

Santiago Squarzon · Accepted Answer · 2025-06-28 18:50:09Z

4

What happens is that indexing ([ ] index operator) works on objects that implement an indexer, and the default individual output from ConvertFrom-Json is a PSCustomObject (a custom object type in PowerShell). The properties of these objects are accessed via dot-notation by default which explains why $jsonContent.$key notation works fine. However, indexing would work by accessing the object's property collection, which does implement Item[string]:

$json = '{ "mykey": "myvalue" }' | ConvertFrom-Json
$key = 'mykey'
$json.psobject.Properties[$key].Value # myvalue

Perhaps, given the context of your question, you're likely coming from a different programming language and very likely you were expecting the output to be a dictionary type, which is totally possible if you're using PowerShell 7+ where you can tell ConvertFrom-Json that you want a dictionary type as output:

$json = '{ "mykey": "myvalue" }' | ConvertFrom-Json -AsHashtable
$key = 'mykey'
$json[$key] # myvalue

However, in Windows PowerShell 5.1 you're quite limited, you could achieve something similar by relying on the behind the scenes serializer used in this version:

Add-Type -AssemblyName System.Web.Extensions

$serializer = [Web.Script.Serialization.JavaScriptSerializer]::new()
$json = $serializer.Deserialize('{ "mykey": "myvalue" }', [hashtable])
$key = 'mykey'
$json[$key] # myvalue

edited Jun 28 at 18:50

answered Jun 21 at 19:09

Santiago Squarzon

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1 Comment

iRon Jun 22 at 7:47

Needless to say, this question has led me to the question behind: "*why can't I access the properties of PS(Custom)Objects throught bracket notation?". If there would be a PowerShell implementation similar to dictionaries (see: #20591), dynamically setting NoteProperties would easier and getting them would be safer...

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