Reuse PowerShell functions in Script Block [duplicate] - powershell

Question

I feel like I'm missing something that should be obvious, but I just can't figure out how to do this.
I have a ps1 script that has a function defined in it. It calls the function and then tries using it remotely:
function foo
{
Param([string]$x)
Write-Output $x
}
foo "Hi!"
Invoke-Command -ScriptBlock { foo "Bye!" } -ComputerName someserver.example.com -Credential someuser#example.com
This short example script prints "Hi!" and then crashes saying "The term 'foo' is not recognized as the name of a cmdlet, function, script file, or operable program."
I understand that the function is not defined on the remote server because it is not in the ScriptBlock. I could redefine it there, but I'd rather not. I'd like to define the function once and use it either locally or remotely. Is there a good way to do this?

Answer 1

You need to pass the function itself (not a call to the function in the ScriptBlock).
I had the same need just last week and found this SO discussion
So your code will become:
Invoke-Command -ScriptBlock ${function:foo} -argumentlist "Bye!" -ComputerName someserver.example.com -Credential someuser#example.com
Note that by using this method, you can only pass parameters into your function positionally; you can't make use of named parameters as you could when running the function locally.

Answer 2

You can pass the definition of the function as a parameter, and then redefine the function on the remote server by creating a scriptblock and then dot-sourcing it:
$fooDef = "function foo { ${function:foo} }"
Invoke-Command -ArgumentList $fooDef -ComputerName someserver.example.com -ScriptBlock {
Param( $fooDef )
. ([ScriptBlock]::Create($fooDef))
Write-Host "You can call the function as often as you like:"
foo "Bye"
foo "Adieu!"
}
This eliminates the need to have a duplicate copy of your function. You can also pass more than one function this way, if you're so inclined:
$allFunctionDefs = "function foo { ${function:foo} }; function bar { ${function:bar} }"

Answer 3

You can also put the function(s) as well as the script in a file (foo.ps1) and pass that to Invoke-Command using the FilePath parameter:
Invoke-Command –ComputerName server –FilePath .\foo.ps1
The file will be copied to the remote computers and executed.

Answer 4

Although that's an old question I would like to add my solution.
Funny enough the param list of the scriptblock within function test, does not take an argument of type [scriptblock] and therefor needs conversion.
Function Write-Log
{
param(
[string]$Message
)
Write-Host -ForegroundColor Yellow "$($env:computername): $Message"
}
Function Test
{
$sb = {
param(
[String]$FunctionCall
)
[Scriptblock]$WriteLog = [Scriptblock]::Create($FunctionCall)
$WriteLog.Invoke("There goes my message...")
}
# Get function stack and convert to type scriptblock
[scriptblock]$writelog = (Get-Item "Function:Write-Log").ScriptBlock
# Invoke command and pass function in scriptblock form as argument
Invoke-Command -ComputerName SomeHost -ScriptBlock $sb -ArgumentList $writelog
}
Test
Another posibility is passing a hashtable to our scriptblock containing all the methods that you would like to have available in the remote session:
Function Build-FunctionStack
{
param([ref]$dict, [string]$FunctionName)
($dict.Value).Add((Get-Item "Function:${FunctionName}").Name, (Get-Item "Function:${FunctionName}").Scriptblock)
}
Function MyFunctionA
{
param([string]$SomeValue)
Write-Host $SomeValue
}
Function MyFunctionB
{
param([int]$Foo)
Write-Host $Foo
}
$functionStack = #{}
Build-FunctionStack -dict ([ref]$functionStack) -FunctionName "MyFunctionA"
Build-FunctionStack -dict ([ref]$functionStack) -FunctionName "MyFunctionB"
Function ExecuteSomethingRemote
{
$sb = {
param([Hashtable]$FunctionStack)
([Scriptblock]::Create($functionStack["MyFunctionA"])).Invoke("Here goes my message");
([Scriptblock]::Create($functionStack["MyFunctionB"])).Invoke(1234);
}
Invoke-Command -ComputerName SomeHost -ScriptBlock $sb -ArgumentList $functionStack
}
ExecuteSomethingRemote