Wrap existing powershell script as function?

Question

I have a script like this:

 [CmdletBinding()]
 param(
    [Parameter(Mandatory=$true)]
    $Message
 )
 Write-Host "Hello, $Message!"

But I want to provide a method that allows users to dot source the script. Initially, I was just thinking I would wrap the whole script in a function to allow dot sourcing:

 function Hello
 {
    [CmdletBinding()]
    param(
       [Parameter(Mandatory=$true)]
       $Message
    )
    Write-Host "Hello, $Message!"
 }

The problem with this is that if I did this, it would break the script for some people who are using it the old way. Is it possible to return an object with the same functionality as the script, or is there a way to dot source the script as it is (the first example above)?

Answer 1

I would suggest using splatting with $PSBoundParameters:

[CmdletBinding()]
 param(
    [Parameter(Mandatory=$true)]
    $Message
 )

 function Hello
 {
    [CmdletBinding()]
    param(
       [Parameter(Mandatory=$true)]
       $Message
    )
    Write-Host "Hello, $Message!"
 }

 Hello @PSBoundParameters

Alternatively: instead of dot-sourcing just create function from existing script:

$code = Get-Content .\HelloScript.ps1
New-Item -Path function:\Hello -Value ([scriptblock]::Create($code))

Answer 2

At the end of function Hello you must trigger it to simulate old behaviour. So if the script used to take an argument from command line, lets say c:\scripts\hello.ps1 bob, you can do it as so:

function Hello
{
   ...
}
if($args.Count -eq 0){
   Hello $null
}
else{
   Hello $args
}

$args will be an empty array if you were to run c:\scripts\newhello.ps1 without an argument, rather than $null as previously when no value was passed. Therefore we check $args.Count before triggering the function with correct parameter.

Answer 3

I know this is incredibly old but I just ran into it while doing something similar. I have a Foo.ps1 script that needs to work as a script but that I would also like available as one function exported from a module. It seems (I just started playing with it) as if putting the following (in Foo.psm1) function Foo { . "$PSScriptRoot\Foo.ps1" } works like a charm. Avoids having to write out all the arguments in two places.