How do I Start a job of a function i just defined?

Question

How do I Start a job of a function i just defined?

function FOO { write-host \"HEY\" } Start-Job -ScriptBlock { FOO } |
Receive-Job

Receive-Job: The term \'         


        

Answer 1

It worked for me as:

Start-Job -ScriptBlock ${Function:FOO}

Answer 2

A slightly different take. A function is just a scriptblock assigned to a variable. Oh, it has to be a threadjob. It can't be foreach-object -parallel.

$func = { 'hi' } # or
function hi { 'hi' }; $func = $function:hi

start-threadjob { & $using:func } | receive-job -auto -wait

hi

Answer 3

@Rynant's suggestion of InitializationScript is great

I thought the purpose of (script) blocks is so that you can pass them around. So depending on how you are doing it, I would say go for:

$FOO = {write-host "HEY"}

Start-Job -ScriptBlock $FOO | wait-job |Receive-Job

Of course you can parameterize script blocks as well:

$foo = {param($bar) write-host $bar}

Start-Job -ScriptBlock $foo -ArgumentList "HEY" | wait-job | receive-job

Answer 4

An improvement to @Rynant's answer:

You can define the function as normal in the main body of your script:

Function FOO 
{ 
  Write-Host "HEY" 
} 

and then recycle this definition within a scriptblock:

$export_functions = [scriptblock]::Create(@"
  Function Foo { $function:FOO }
"@)

(makes more sense if you have a substantial function body) and then pass them to Start-Job as above:

Start-Job -ScriptBlock {FOO} -InitializationScript $export_functions| Wait-Job | Receive-Job

I like this way, as it is easier to debug jobs by running them locally under the debugger.

Answer 5

@Ben Power's comment under the accepted answer was my concern also, so I googled how to get function definitions, and I found Get-Command - though this gets only the function body. But it can be used also if the function is coming from elsewhere, like a dot-sourced file. So I came up with the following (hold my naming convention :)), the idea is to re-build the function definitions delimited by newlines:

Filter Greeting {param ([string]$Greeting) return $Greeting}
Filter FullName {param ([string]$FirstName, [string]$LastName) return $FirstName + " " + $LastName}
$ScriptText = ""
$ScriptText += "Filter Greeting {" + (Get-Command Greeting).Definition + "}`n"
$ScriptText += "Filter FullName {" + (Get-Command FullName).Definition + "}`n"
$Job = Start-Job `
            -InitializationScript $([ScriptBlock]::Create($ScriptText)) `
            -ScriptBlock {(Greeting -Greeting "Hello") + " " + (FullName -FirstName "PowerShell" -LastName "Programmer")}
$Result = $Job | Wait-Job | Receive-Job
$Result
$Job | Remove-Job

Answer 6

As @Shay points out, FOO needs to be defined for the job. Another way to do this is to use the -InitializationScript parameter to prepare the session.

For your example:

$functions = {
    function FOO { write-host "HEY" }
}

Start-Job -InitializationScript $functions -ScriptBlock {FOO}|
    Wait-Job| Receive-Job

This can be useful if you want to use the same functions for different jobs.