how to prevent PowerShell adding \ to a string - json

Question

I'm currently working with Powershell editing JSONs
My JSON looks like this:
{
"value": ["E_"]
}
I only want to add a specific number after E_.
The result should look like this:
{
"value": ["E_5"]
}
My PS Script:
$tdePath = 'C:\temp\tde.csv'
$dirName = Get-ChildItem -Path $rootDir -Filter TDE_Config.json -Recurse -ErrorAction SilentlyContinue -Force | Select-Object DirectoryName | Export-Csv $tdePath -NoTypeInformation
$importTDEJson = Import-Csv $tdePath -Encoding UTF8 | % {
[String]$nr = $_.DirectoryName.Split('\')[6].split(' ')[4]
$full_path = $_.DirectoryName + "\TDE_Config.json"
[int]$nr2 = $nr -as [int] #Convert String to Int to convert 004 -> 4
$a = Get-Content $full_path -raw | ConvertFrom-Json
$a.value= "[`"E_" + $nr2 + "`"]"
$a | ConvertTo-Json | set-content $full_path -Force
}
Only excuting "[`"E_" + $nr2 + "`"]" returns the value I need.
For example if $nr2 = 145 it returns in ps console
["E_145"]
But my JSON looks like this:
{
"value": "[\"E_145\"]"
}
Why is powershell adding \ to my string?
How can I prevent powershell adding \ to my string?

Answer 1

You are mixing Json by hand and Json by ConvertTo-Json.
Powershell is doing javascript escaping of the backslashes you insert. Just set $a.value like this:
$a.value= #("E_$nr2")
That will create an array and the Json conversion will do the rest for you.
EDIT:
Here is a proof of concept:
$a = [pscustomobject]#{
value = 'Something else'
}
$nr2 = 145
$a.value= #("E_$nr2")
$a | ConvertTo-Json
outputs:
{
"value": [
"E_145"
]
}