First parameter in PowerShell function loses its value? - powershell

Question

Here's a function that I call with .\GetEMSInstallers. For some unknown reason the first parameter always loses its value:
function Get-EMSInstallers {
param (
$ems_for_amx_source = '\\server\ems_path',
$installers_dir = 'D:\installers'
)
process {
if (!(Test-Path "$installers_dir\EMS4AMX")) {
"Copying files and folders from $ems_for_amx_source to $installers_dir\EMS4AMX"
copy $ems_for_amx_source "$installers_dir\EMS4AMX" -rec -force
}
}
}
Get-EMSInstallers $args
When I call it I get this output:
Copying files and folders from to D:\installers\EMS4AMX
Copy-Item : Cannot bind argument to parameter 'Path' because it is an empty array.
At C:\Users\ad_ctjares\Desktop\Scripts\Ems\GetEMSInstallers.ps1:12 char:17
+ copy <<<< $ems_for_amx_source "$installers_dir\EMS4AMX" -rec -force
+ CategoryInfo : InvalidData: (:) [Copy-Item], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationErrorEmptyArrayNotAllowed,Microsoft.PowerShell.Commands.CopyI
temCommand

Answer 1

When you don't pass in any argument to Get-EMSInstallers you still have a $args array - it is just empty. So the $ems_for_amx_source parameters is set to this empty array.
In other words, one way around this:
if ($args)
{
Get-EMSInstallers $args
}
else
{
Get-EMSInstallers
}
There is probably a more powershelly way to do this - I might revise this later if it comes to mind. :-) But that will get you started anyway.