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

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 'FOO' is not recognized as the name of cmdlet,
function ,script file or operable program.
What do I do?
Thanks.

Answer 1

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.

Answer 2

#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 3

It worked for me as:
Start-Job -ScriptBlock ${Function:FOO}

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

The function needs to be inside the scriptblock:
Start-Job -ScriptBlock { function FOO { write-host "HEY" } ; FOO } | Wait-Job | Receive-Job

Answer 6

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 7

#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 8

As long as the function passed to the InitializationScript param on Start-Job isn't large Rynant's answer will work, but if the function is large you may run into the below error.
[localhost] There is an error launching the background process. Error
reported: The filename or extension is too long"
Capturing the function's definition and then using Invoke-Expression on it in the ScriptBlock is a better alternative.
function Get-Foo {
param
(
[string]$output
)
Write-Output $output
}
$getFooFunc = $(Get-Command Get-Foo).Definition
Start-Job -ScriptBlock {
Invoke-Expression "function Get-Foo {$using:getFooFunc}"
Get-Foo -output "bar"
}
Get-Job | Receive-Job
PS C:\Users\rohopkin> Get-Job | Receive-Job
bar