How can I force Powershell to return an array when a call only returns one object?
PowershellPowershell Problem Overview
I'm using Powershell to set up IIS bindings on a web server, and having a problem with the following code:
$serverIps = gwmi Win32_NetworkAdapterConfiguration
| Where { $_.IPAddress }
| Select -Expand IPAddress
| Where { $_ -like '*.*.*.*' }
| Sort
if ($serverIps.length -le 1) {
Write-Host "You need at least 2 IP addresses for this to work!"
exit
}
$primaryIp = $serverIps[0]
$secondaryIp = $serverIps[1]
If there's 2+ IPs on the server, fine - Powershell returns an array, and I can query the array length and extract the first and second addresses just fine.
Problem is - if there's only one IP, Powershell doesn't return a one-element array, it returns the IP address (as a string, like "192.168.0.100") - the string has a .length
property, it's greater than 1, so the test passes, and I end up with the first two characters in the string, instead of the first two IP addresses in the collection.
How can I either force Powershell to return a one-element collection, or alternatively determine whether the returned "thing" is an object rather than a collection?
Powershell Solutions
Solution 1 - Powershell
Define the variable as an array in one of two ways...
Wrap your piped commands in parentheses with an @
at the beginning:
$serverIps = @(gwmi Win32_NetworkAdapterConfiguration
| Where { $_.IPAddress }
| Select -Expand IPAddress
| Where { $_ -like '*.*.*.*' }
| Sort)
Specify the data type of the variable as an array:
[array]$serverIps = gwmi Win32_NetworkAdapterConfiguration
| Where { $_.IPAddress }
| Select -Expand IPAddress
| Where { $_ -like '*.*.*.*' }
| Sort
Or, check the data type of the variable...
IF ($ServerIps -isnot [array])
{ <error message> }
ELSE
{ <proceed> }
Solution 2 - Powershell
Force the result to an Array so you could have a Count property. Single objects (scalar) do not have a Count property. Strings have a length property so you might get false results, use the Count property:
if (@($serverIps).Count -le 1)...
By the way, instead of using a wildcard that can also match strings, use the -as operator:
[array]$serverIps = gwmi Win32_NetworkAdapterConfiguration -filter "IPEnabled=TRUE" | Select-Object -ExpandProperty IPAddress | Where-Object {($_ -as [ipaddress]).AddressFamily -eq 'InterNetwork'}
Solution 3 - Powershell
You can either add a comma(,
) before return list like return ,$list
or cast it [Array]
or [YourType[]]
at where you tend to use the list.
Solution 4 - Powershell
If you declare the variable as an array ahead of time, you can add elements to it - even if it is just one...
This should work...
$serverIps = @()
gwmi Win32_NetworkAdapterConfiguration
| Where { $_.IPAddress }
| Select -Expand IPAddress
| Where { $_ -like '*.*.*.*' }
| Sort | ForEach-Object{$serverIps += $_}
Solution 5 - Powershell
You can use Measure-Object
to get the actual object count, without resorting to an object's Count
property.
$serverIps = gwmi Win32_NetworkAdapterConfiguration
| Where { $_.IPAddress }
| Select -Expand IPAddress
| Where { $_ -like '*.*.*.*' }
| Sort
if (($serverIps | Measure).Count -le 1) {
Write-Host "You need at least 2 IP addresses for this to work!"
exit
}
Solution 6 - Powershell
Return as a referenced object, so it never converted while passing.
return @{ Value = @("single data") }
Solution 7 - Powershell
I had this problem passing an array to an Azure deployment template. If there was one object, PowerShell "converted" it to a string. In the example below, $a
is returned from a function that gets VM objected according to the value of a tag. I pass the $a
to the New-AzureRmResourceGroupDeployment
cmdlet by wrapping it in @()
. Like so:
$TemplateParameterObject=@{
VMObject=@($a)
}
New-AzureRmResourceGroupDeployment -ResourceGroupName $RG -Name "TestVmByRole" -Mode Incremental -DeploymentDebugLogLevel All -TemplateFile $templatePath -TemplateParameterObject $TemplateParameterObject -verbose
VMObject
is one of the template's parameters.
Might not be the most technical / robust way to do it, but it's enough for Azure.
Update
Well the above did work. I've tried all the above and some, but the only way I have managed to pass $vmObject
as an array, compatible with the deployment template, with one element is as follows (I expect MS have been playing again (this was a report and fixed bug in 2015)):
[void][System.Reflection.Assembly]::LoadWithPartialName("System.Web.Extensions")
foreach($vmObject in $vmObjects)
{
#$vmTemplateObject = $vmObject
$asJson = (ConvertTo-Json -InputObject $vmObject -Depth 10 -Verbose) #-replace '\s',''
$DeserializedJson = (New-Object -TypeName System.Web.Script.Serialization.JavaScriptSerializer -Property @{MaxJsonLength=67108864}).DeserializeObject($asJson)
}
$vmObjects
is the output of Get-AzureRmVM.
I pass $DeserializedJson
to the deployment template' parameter (of type array).
For reference, the lovely error New-AzureRmResourceGroupDeployment
throws is
"The template output '{output_name}' is not valid: The language expression property 'Microsoft.WindowsAzure.ResourceStack.Frontdoor.Expression.Expressions.JTokenExpression'
can't be evaluated.."