How can I force Powershell to return an array when a call only returns one object?

Question

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?

Answer 1

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> }

Answer 2

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'}