How can I use splatting in a parameterized function? - powershell

Question

I'm writing a parameterized function and trying to use splatting to reuse the parameter-set.
$Computername='localhost'
$params = #{'computername'=$Computername;
'credential'='administrator'}
function Get-Diskinfo {
Param ($drive,$computername,$credential)
Get-WmiObject win32_logicaldisk -Filter "DeviceID = '$drive'" #params
}
On executing like this it fails doesn't recognize the user-inputed servername. It still takes the value of $Computername initially specified.
Get-Diskinfo -drive c: Server1 administrator
How can I get it to identify the user-inputed computername? Am I missing something ?

Answer 1

Instead of splatting random hashtable, you need to splat something that is defined automatically by PowerShell:
function Get-Diskinfo {
Param ($drive,$computername,$credential)
# Need to remove any parameter that is used "internally" and don't exist on cmdlet
$PSBoundParameters.Remove('drive') | Out-Null
Get-WmiObject win32_logicaldisk -Filter "DeviceID = '$drive'" #PSBoundParameters
}
Get-Diskinfo -drive c: Server1 administrator
Alternatively: use passed parameters to build $parms inside your function:
function Get-Diskinfo {
Param ($drive,$computername,$credential)
$parms = #{
computername = $Computername
credential = $credential
}
Get-WmiObject win32_logicaldisk -Filter "DeviceID = '$drive'" #parms
}

Answer 2

You aren't calling #parms until inside your function.
This should work, using the parameters within your function to pull the WMI query:
$Computername='localhost'
$parms = #{'computername'=$Computername;
'credential'='administrator'}
function Get-Diskinfo {
Param ($drive,$computername,$credential)
Get-WmiObject win32_logicaldisk -Filter "DeviceID = '$drive'" -ComputerName $computername -Credential $credential
}
And then use the splatting to run the function:
Get-Diskinfo -drive c: #parm
The function can still be run using the parameters directly:
Get-Diskinfo -drive c: Server1 administrator

Answer 3

Your $params hashtable gets it's value when you create it, not when it's used. Your $computername,$credential parameters are never referenced inside your function, which means that they are dead parameters.
You can't use splatting and normal function-calling with parameters for the same parameter at the same time. You should only use parameters inside your function scriptblock. Splatting is for the end-user only. #Tim Ferril has shown you how to write the function properly.
If you need to be able to use both default values AND be able to change ex. ComputerName for one cmdlet, then you should use default values and not splatting. Ex:
function Test-Global {
param(
$ComputerName = $global:PC,
$Username = $global:username
)
"Computername is '$ComputerName'"
"Username is '$UserName'"
}
#Set the reusable variables in global scope and call your function
$global:Username = "Frode"
$global:PC = "MyPC"
PS C:\Users\Frode> Test-Global
Computername is 'MyPC'
Username is 'Frode'
#If I need to modify the server for one function, I'd simply specify that parameter
PS C:\Users\Frode> Test-Global -ComputerName server1
Computername is 'server1'
Username is 'Frode'
To make it easier for user to set the default values, you could create a function for that too.
#Create your reusable parameters
function Set-Params {
param(
$ComputerName,
$Username
)
if($Username) { $global:Username = $Username }
if($ComputerName) { $global:PC = $ComputerName }
}
PS C:\Users\Frode> Set-Params -ComputerName Test1 -Username Test1
PS C:\Users\Frode> Test-Global
Computername is 'Test1'
Username is 'Test1'
PS C:\Users\Frode> Set-Params -ComputerName Test2
PS C:\Users\Frode> Test-Global
Computername is 'Test2'
Username is 'Test1'