Same Parameter name, different scope, same value. How to deal? - powershell

Question

# cmdlet MyCmdlet.ps1
Param(
[Parameter(Mandatory=$true)]
[string]$Variable1,
[string]$Variable2
)
Begin {
Function Function-Name {
Param (
[Parameter(Mandatory=$true)]
[string]$Variable1,
[Parameter(Mandatory=$false)]
[string]$Variable2,
[Parameter(Mandatory=$false)]
[ValidateScript({[string]::IsNullOrWhiteSpace($Variable2)})]
[switch]$Choice
)
# function-body
}
}
Process {
Function-name -Variable1 "SomeString" -Choice
}
This cmdlet was called like below:
.\MyCmdlet.ps1 -variable1 "string1" -variable2 "string2"
It returns:
Cannot validate argument on parameter 'choice'. The "[string]::IsNullOrWhiteSpace($Variable2) " validation script for the argument with value "True" did not return a result of True.
It seems like the value of -Variable2 of cmdlet was implicitly passed to the function because of same variable name even without specically mentioning it during the function call inside the cmdlet.
Note: I need the variables to have same name so I can see their similar function in the future. And I use Begin, Process, End in cmdlet just so I can convert it into function and put in inside other scripts.
How can I deal with this?

Answer 1

By the time the ValidationScript runs, the local variable $Variable2 has not yet been created, so you get the value from $Variable2 in the parent scope.
Use $PSBoundParameters instead:
Function Function-Name {
Param (
[Parameter(Mandatory=$true)]
[string]$Variable1,
[Parameter(Mandatory=$false)]
[string]$Variable2,
[Parameter(Mandatory=$false)]
[ValidateScript({[string]::IsNullOrWhiteSpace($PSBoundParameters['Variable2'])})]
[switch]$Choice
)
}

Answer 2

If your intention is to create a script that could be both invoked directly (as a script) and dot-sourced (so you can call the function in it from other PowerShell scripts), you could do something like this:
# Invoke-Something.ps1
[CmdletBinding()]
Param(
[Parameter(Mandatory=$false)]
[string]$Variable1,
[Parameter(Mandatory=$false, ParameterSetName='bar')]
[string]$Variable2,
[Parameter(Mandatory=$true, ParameterSetName='foo')]
[switch]$Choice
)
function Invoke-Something {
[CmdletBinding()]
Param (
[Parameter(Mandatory=$true)]
[string]$Variable1,
[Parameter(Mandatory=$false, ParameterSetName='bar')]
[string]$Variable2,
[Parameter(Mandatory=$true, ParameterSetName='foo')]
[switch]$Choice
)
Write-Host 'invocation: function'
}
if ($MyInvocation.Line.Split()[0] -ne '.') {
Write-Host 'invocation: directly'
Invoke-Something #PSBoundParameters
} else {
Write-Host 'invocation: dot-source'
}
Using the above approach you can invoke the script directly:
PS> Invoke-Something.ps1 -Variable1 'some' -Variable2 'other'
invocation: directly
invocation: function
or dot-source it and invoke the function:
PS> . Invoke-Something.ps1
invocation: dot-source
PS> Invoke-Something -Variable1 'some' -Variable2 'other'
invocation: function
For this to work you must make all parameters of the script optional, though.
A simplified version of this would not define parameters on the script level and pass #args to the invoked function:
# Invoke-Something.ps1
function Invoke-Something {
[CmdletBinding()]
Param (
[Parameter(Mandatory=$true)]
[string]$Variable1,
[Parameter(Mandatory=$false, ParameterSetName='bar')]
[string]$Variable2,
[Parameter(Mandatory=$true, ParameterSetName='foo')]
[switch]$Choice
)
Write-Host 'invocation: function'
}
if ($MyInvocation.Line.Split()[0] -ne '.') {
Write-Host 'invocation: directly'
Invoke-Something #args
} else {
Write-Host 'invocation: dot-source'
}