PowerShell: Passing an ArrayList of Objects into another Script as an Argument

Question

I am trying to pass an ArrayList that contains objects into another PowerShell script to execute something further.

The error message that I am receiving is:

"Cannot process argument transformation on parameter 'al'. Cannot convert the "System.Collections.Hashable System.Collections.Hashable System.Collections.Hashable" value of type "System.String" to type "System.Collections.ArrayList""

In script1.ps1:

$al = New-Object System.Collections.ArrayList

...

$obj =  @{"var1"="apple"; "var2"="banana"; "var3"="carrot";}
$al.Add($obj)

...


foreach ($i in $al) {
    $temp = $($i.var1)
    write-host "$temp"     #outputs "apple" correctly
}

invoke-expression -Command "script2.ps1 -al '$al'"

In script2.ps1:

param ([System.Collections.ArrayList]$al)

...

foreach ($i in $al) {
    $temp = $($i.var1)
    write-host "$temp"     #error message
}

one very simple way to pass structured data between PoSh scripts is to use one of the structured data file types. JSON is the most often recommended, but the Export/Import-CliXml cmdlets handle PoSh data types very neatly. so i would export to a CliXml file & then have the other script import that file. that way all you need to pass is the full file name. [grin] — Lee_Dailey
– Lee_Dailey, Commented May 2, 2020 at 13:46
Please consider upvoting any answers you found helpful, or accepting an answer (via the checkbox) if it solves your problem. — derekbaker783
– derekbaker783, Commented May 3, 2020 at 15:18

derekbaker783 · Accepted Answer · 2020-05-02 13:24:41Z

2

For a reason that I'm not familiar with, Invoke-Expression is converting your ArrayList to a HashTable. If you really need an ArrayList in script2.ps1, you can make $al a global variable (see below).

Updated script1.ps1

$al = New-Object System.Collections.ArrayList
$obj = @{"var1" = "apple"; "var2" = "banana"; "var3" = "carrot"; }
$al.Add($obj)

foreach ($i in $al) {
    $temp = $($i.var1)
    write-host "$temp"     
}

$Global:al = $al

invoke-expression -Command "$PSScriptRoot\script2.ps1"

Updated script2.ps1

param()

$Global:al.GetType().FullName

foreach ($i in $Global:al) {
    $temp = $($i.var1)
    write-host "$temp"     
}

edited May 2, 2020 at 13:24

answered May 2, 2020 at 13:16

derekbaker783

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3 Comments

Ash Over a year ago

$obj is creating a hashtable that he is adding to his ArrayList.

derekbaker783 Over a year ago

@Ash, $al still an still an ArrayList when used by Invoke-Expression. This can verify this by adding $al.GetType().FullName to the line before the one where script2.ps1` is invoked.

Ash Over a year ago

He's then converting it to a string by wrapping the variable in quotes, which is causing the problem. In reality it works. I think you still need to choose whether you need a key/value pairing such as a hashtable or dictionary, or a List/Array of objects. I'm not sure a list of hashtables is particularly helpful.

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