What am I doing wrong on PowerShell function parameters?

Question

I would really appreciate it if somebody could point out what I am doing wrong in passing parameters from a function back to the mainline code. I have a variable which has been successfully extracted in a function, but I cannot seem to pass that back to the mainline code

This is the code I am using:

function get-field ($field, $heading) {
    $fieldPos = $script:source.AllElements.InnerText.IndexOf($heading) +1
    $field = $script:source.AllElements.InnerText[$fieldPos]    

    # If states "Not Available", or contains a heading, process as if not found.
    if ($field -eq "Not Available ") {$fieldPos = 0}
    if ($field -eq $heading) {$fieldPos = 0}

    # Check that a valid entry was received
    if ($fieldPos -eq 0) {
        Write-Host "Warning:" $heading "was not found" 
    } else {
        $field = $field.Trim()
    }

    return $field
}    

get-field $email "Name"
get-field $address "Address"

I have verified that within the function, the $field and $heading parameters contain the correct information, so why aren't the $email and $address fields being populated?

Maybe I dont fully understand the function, but it does not seem like you populate the variables anywhere. You return $field but dont save it anywhere when you call the funtction. Without knowing the function, does $email = get-field $email "Name" solve the problem? — Paxz
– Paxz, Commented Jul 24, 2018 at 7:07

TobyU · Accepted Answer · 2018-07-24 07:20:16Z

2

You're not doing it totally wrong.

Have a look at this example:

function get-field ($field, $heading) {

    return "$field - $heading"
}

$address = get-field "AddressFiled" "AddressHeading"
$address

to catch the returned value in a variable for further use, you should call the function like in the above example.

edited Jul 24, 2018 at 7:20

answered Jul 24, 2018 at 7:08

TobyU

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1 Comment

Lee Over a year ago

Thank you. That has been driving me crazy; all I needed to do was to put the $address = before calling the function. Thanks for your help!

Ansgar Wiechers · Accepted Answer · 2018-07-24 11:40:00Z

Parameters in PowerShell are normally used for passing values into a function. The output of a function must be assigned to a variable in the statement that invokes the function. Also, it's bad design to use global variables inside a function, because that makes debugging significantly more difficult.

Your code should look somewhat like this:

function Get-Field ($data, $heading) {
    $fieldPos = $data.IndexOf($heading) + 1
    $field    = $data[$fieldPos].Trim()

    # If states "Not Available", or contains a heading, process as if not found.
    if ($field -eq 'Not Available' -or $field -eq $heading) {
        Write-Host "Warning: ${heading} was not found" 
    }

    $field
}    

$email   = Get-Field $script:source.AllElements.InnerText 'Name'
$address = Get-Field $script:source.AllElements.InnerText 'Address'

You can have out parameters if you want to, but they're rather uncommon in PowerShell, probably because they're not as straight-forward to use as one would like.

function Get-Field ([ref]$field, $data, $heading) {
    $fieldPos    = $data.IndexOf($heading) + 1
    $field.Value = $data[$fieldPos].Trim()

    # If states "Not Available", or contains a heading, process as if not found.
    if ($field -eq 'Not Available' -or $field -eq $heading) {
        Write-Host "Warning: ${heading} was not found" 
    }
}    

$email = $null
Get-Field ([ref]$email) $script:source.AllElements.InnerText 'Name'
$address = $null
Get-Field ([ref]$address) $script:source.AllElements.InnerText 'Address'

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