Unable to fetch data using powershell as external data source - terraform

Question

# main.tf
data "external" "extDateTime" {
program = ["pwsh", "${path.module}/getDateTime.ps1"]
}
output "value" {
value = "${data.external.extDateTime.result.dateTime}"
}
This is the Powershell file getDateTime.ps1 code section
# getDateTime.ps1
$DateTime = Get-Date -Format "yyyyMMddHHmmss"
Write-Output "{""dateTime"": $DateTime}"
Then I run the following command: terraform plan
Error: Unexpected External Program Results with data.external.extDateTime, on main.tf line 26, in data "external" "extDateTime":
26: program = ["Powershell.exe", "${path.module}/getDateTime.ps1"]
The data source received unexpected results after executing the program. Program output must be a JSON encoded map of string keys and string values.
Program: C:\WINDOWS\System32\WindowsPowerShell\v1.0\Powershell.exe
Result Error: invalid character '{' after top-level value
My understanding is the PS script has to return in JSON format but I keep getting the Result Error. Any ideas would be appreciated.

Answer 1

Ensure that the JSON values are correctly formatted as strings (using back ticks to escape double quotes):
$DateTime = Get-Date -Format "yyyyMMddHHmmss"
Write-Output "{`"dateTime`": `"$DateTime`"}"
As per the Terraform docs for the external data source:
The JSON object contains the contents of the query argument and its values will always be strings.
Another way that this can be done is to create a PowerShell custom object and convert it to JSON:
$DateTime = Get-Date -Format "yyyyMMddHHmmss"
$myObject = [PSCustomObject]#{
dateTime = $DateTime
}
ConvertTo-Json $myObject
If you need the output to be a number, you can use the tonumber() function:
output "value" {
value = tonumber(data.external.extDateTime.result.dateTime)
}

Answer 2

I figured out what the issue was. I was running terraform commands in PS 7 (pwsh.exe) but my data.external program was calling PS 5 (powershell.exe). Once I updated to the following: program = ["pwsh.exe", "${path.module}/getDateTime.ps1"] it worked fine. The error message referring to the { was misleading me. Thanks again Cody.