CODEWITHSUNDEEP
powershell
Bionic
Bionic

Reputation: 93

Powershell passing argument values to parameters and back

Alright. I'm attempting to complete a school assignment and cannot for the life of me figure this out. I'm trying to use powershell to pass values from one function to another making a "modular" type script. I can't seem to figure out how to move the values out of the scope of the function without using the $script:xxxxx. Is there another way to move the values in powershell as a regular argument parameter pass by reference?

Here's what I have:

function main
{
inputGrams($carbGrams, $fatGrams)
$carbGrams
$carbGrams
calcGrams
displayInfo
}

function inputGrams([ref]$carbGrams, [ref]$fatGrams)
{
    $carbGrams = read-host "Enter the grams of carbs per day"
    $fatGrams = read-host "Enter the grams of fat per day"
}

function calcGrams
{
    $carbCal = $carbGrams * 4
    $fatCal = $fatGrams * 9
}

function displayInfo 
{
    write-host "The total amount of carb calories is $carbCal" 
    write-host "The total amount of fat calories is $fatCal"
}

main

The two values right after the inputGrams function should change each time the script is run but they don't because of scope issues and passing the values. Anyone know how to properly pass those values back to the main function?

Upvotes: 7

Views: 26550

Answers (2)

zx38
zx38

Reputation: 114

Andy is on the right path but [Ref] are tricky and it is recommended to avoid them if you can.

As you said, the problem is scope. All your functions —except main— are called from main, therefore you need to make the variables available to these functions by setting them in main's scope, i.e. their parent scope, with Set-Variable or New-Variable.

Same point is valid when retrieving their values with Get-Variable.

function main
{
    inputGrams
    $carbGrams
    $fatGrams
    calcGrams
    displayInfo
}

function inputGrams
{
    # type constrain as Single because Read-Host returns a String
    [single]$carbs = read-host "Enter the grams of carbs per day"
    [single]$fat = read-host "Enter the grams of fat per day"

    # scope 1 is the parent scope, i.e. main's scope
    Set-Variable -Name carbGrams -Value $carbs -Scope 1
    Set-Variable -Name fatGrams -Value $fat -Scope 1
}

function calcGrams
{
    # scope 1 is the parent scope, i.e. main's scope
    Set-Variable -Name carbCal -Value ($carbGrams * 4) -Scope 1
    Set-Variable -Name fatCal -Value ($fatGrams * 9) -Scope 1
}

function displayInfo 
{
    # scope 1 is the parent scope, i.e. main's scope
    $_carbCal = Get-Variable -Name carbCal -Scope 1 -ValueOnly
    $_fatCal = Get-Variable -Name fatCal -Scope 1 -ValueOnly

    write-host "The total amount of carb calories is $_carbCal" 
    write-host "The total amount of fat calories is $_fatCal"
}

main

PS: I hope I did not spoil your school assignment, just wanted to help out ;)

Upvotes: 0

Andy Arismendi
Andy Arismendi

Reputation: 52699

There are a few problems. First here's a working example:

function main
{
    # 1. Create empty variable first.
    New-Variable -Name carbGrams
    New-Variable -Name fatGrams

    # 2. Spaces in between parameters. Not enclosed in parens.
    # 3. Put REF params in parens.
    inputGrams ([ref]$carbGrams) ([ref]$fatGrams)

    $carbGrams
    $fatGrams
}

function inputGrams( [ref]$carbGrams, [ref]$fatGrams )
{
    # 4. Set the Value property of the reference variable.
    $carbGrams.Value = read-host "Enter the grams of carbs per day"
    $fatGrams.Value = read-host "Enter the grams of fat per day"
}

main

And explanation:

  1. You'll need to create the variable before passing it by REF.
  2. Don't enclose PowerShell function params in parens, just separate them with spaces.
  3. Put the REF arguments in parens.
  4. To set the REF variable's value, you'll need to set the Value property.

Upvotes: 15

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