How to collect returns from recursive function calls without a global var?

Question

Usually global variables shouldnt be used, I was told. Ok. But:
How can I avoid using a global var when recursively using a function, when the function returns an object and when I want to have the collection of all these objects as the result?
For example, I think of determine the users of a group including group nesting. I would write a function that adds the direct group members to a collection as a global var and call itself recusively if a member is another group. This recursively called function
would do as well: Update the global var and if needed call itself.
I'm afraid this is no good programming style. What algorithm would be better, prettier? Please dont focus on the example, it is a more general question of how to do.
Thanks
Walter

Answer 1

I rarely needed to create/use recursive functions. Here's one example I did:
function New-SBSeed {
<#
.Synopsis
Function to create files for disk performance testing. Files will have random numbers as content.
File name will have 'Seed' prefix and .txt extension.
.Description
Function will start with the smallest seed file of 10KB, and end with the Seed file specified in the -SeedSize parameter.
Function will create seed files in order of magnitude starting with 10KB and ending with 'SeedSize'.
Files will be created in the current folder.
.Parameter SeedSize
Size of the largest seed file generated. Accepted values are:
10KB
100KB
1MB
10MB
100MB
1GB
10GB
100GB
1TB
.Example
New-SBSeed -SeedSize 10MB -Verbose
This example creates seed files starting from the smallest seed 10KB to the seed size specified in the -SeedSize parameter 10MB.
To see the output you can type in:
Get-ChildItem -Path .\ -Filter *Seed*
Sample output:
Mode LastWriteTime Length Name
-a--- 8/6/2014 8:26 AM 102544 Seed100KB.txt
-a--- 8/6/2014 8:26 AM 10254 Seed10KB.txt
-a--- 8/6/2014 8:39 AM 10254444 Seed10MB.txt
-a--- 8/6/2014 8:26 AM 1025444 Seed1MB.txt
.Link
https://superwidgets.wordpress.com/category/powershell/
.Notes
Function by Sam Boutros
v1.0 - 08/01/2014
#>
[CmdletBinding(SupportsShouldProcess=$true,ConfirmImpact='Low')]
Param(
[Parameter(Mandatory=$true,
ValueFromPipeLine=$true,
ValueFromPipeLineByPropertyName=$true,
Position=0)]
[Alias('Seed')]
[ValidateSet(10KB,100KB,1MB,10MB,100MB,1GB,10GB,100GB,1TB)]
[Int64]$SeedSize
$Acceptable = @(10KB,100KB,1MB,10MB,100MB,1GB,10GB,100GB,1TB)
$Strings = @("10KB","100KB","1MB","10MB","100MB","1GB","10GB","100GB","1TB")
for ($i=0; $i -lt $Acceptable.Count; $i++) {
if ($SeedSize -eq $Acceptable[$i]) { $Seed = $i }
$SeedName = "Seed" + $Strings[$Seed] + ".txt"
if ($Acceptable[$Seed] -eq 10KB) { # Smallest seed starts from scratch
$Duration = Measure-Command {
do {Get-Random -Minimum 100000000 -Maximum 999999999 |
out-file -Filepath $SeedName -append} while ((Get-Item $SeedName).length -lt $Acceptable[$Seed])
} else { # Each subsequent seed depends on the prior one
$PriorSeed = "Seed" + $Strings[$Seed-1] + ".txt"
if ( -not (Test-Path $PriorSeed)) { New-SBSeed $Acceptable[$Seed-1] } # Recursive function :)
$Duration = Measure-Command {
$command = @'
cmd.exe /C copy $PriorSeed+$PriorSeed+$PriorSeed+$PriorSeed+$PriorSeed+$PriorSeed+$PriorSeed+$PriorSeed+$PriorSeed+$PriorSeed $SeedName /y
Invoke-Expression -Command:$command
Get-Random -Minimum 100000000 -Maximum 999999999 | out-file -Filepath $SeedName -append
Write-Verbose ("Created " + $Strings[$Seed] + " seed $SeedName file in " + $Duration.TotalSeconds + " seconds")
This is part of the SBTools module and is used by the
Test-SBDisk function. 
Example use:
New-SBSeed 10GB -Verbose
Test-SBDisk is a multi-threaded function that puts IO load on target disk subsystem and can be used to simulate workloads from multiple machines hitting the same SAN at the same time, and measure disk IO and performance.
Sam Boutros, Senior Consultant, Software Logic, KOP, PA http://superwidgets.wordpress.com (Please take a moment to Vote as Helpful and/or Mark as Answer, where applicable) _________________________________________________________________________________
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