Powershell - New-Variable "-name" defined by function variable

Question

I want to have a function in which the result is stored in a variable where the function defines the variable name - essentially this:

function testfunction ($varname,$text){
    $readhost = read-host -prompt "$text"
    new-variable -name $varname -value $readhost
}

though when entering:

testfunction outputvar sampletext

get-variable -name outputvar

I just get an error that the variable "outputvar" doesnt exist. what am I missing here? Tried a number of other stuff but nothing seemed to work - what i want in the end is a variable that is named "outputvar" that contains the prompt input, just to clarify.

This is due to scoping. Variables created with a function are scoped (only accessible) to that function. You can use $global: to create a global variable, but it would be better to just return a value to a variable. I'll write an answer with an example. — Mark Wragg
– Mark Wragg, Commented Mar 29, 2018 at 9:32

Mark Wragg · Accepted Answer · 2018-03-29 09:35:22Z

5

Your issue is due to scoping. The variable created via New-Variable is (by default) scoped so that it is only accessible within your function. You can override the scope via the -Scope parameter:

function testfunction ($varname,$text){
    $readhost = read-host -prompt "$text"
    new-variable -name $varname -value $readhost -scope Script
}

This changes the scope to Script and so the variable is now accessible outside of your function. Defining non-standard scopes for your variables isn't very good practice however. You should instead just be doing this:

function testfunction ($text){
    read-host -prompt "$text"
}

$outputvar = testfunction sampletext

answered Mar 29, 2018 at 9:35

Mark Wragg

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3 Comments

Flying Thunder Over a year ago

Thanks, i tried to keep the variable in the function so i dont have to repeat it for every use for the function - just out of curiousity, why exactly is it not a good practice? edit: i used $readhost = read-host in the first place because i was using a do - while loop though, but i guess that could work with a pipeline instead

Mark Wragg Over a year ago

Its just because scopes exist for a reason, to keep variables where they are needed and avoid confusion/errors that could occur if the same variable name was used elsewhere. If you wanted to loop around read-host you could still do that and then just output its value at the end: while (-not $readhost) { $readhost = read-host }; $readhost

Flying Thunder Over a year ago

forgot to add, im looping it while input is $null - im not quite sure how i should implement your example code, can you explain a little what this does?

Mathias R. Jessen · Accepted Answer · 2018-03-29 09:42:49Z

2

Use the -OutVariable common parameter. To have your function support common parameters, add the CmdletBinding attribute decorator to the param block:

function Test-Function {
  [CmdletBinding()]
  param($text)

  return Read-Host -Prompt $text
}

Test-Function -OutVariable sampletext |Out-Null
$sampletext

answered Mar 29, 2018 at 9:42

Mathias R. Jessen

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