PowerShell How to convert Get-ChildItem output to a string array - arrays

Question

Alright, been working on this for hours and researching like crazy, but still not getting something to work. I need a string[] object created from get-childitem to pass to the Copy-Item -exclude parameter.
The hurdle is that I need to do recursion and need to have relative paths, so this is what I came up with:
$((Get-ChildItem -Path $Dest -Recurse -File).FullName.TrimStart($Dest))
This results in a clean list of existing files in $dest that are presented with a relative path to $dest. The problem is, if I add this to the copy-item -exclude parameter it seems to ignore it. Further research online suggests that copy-item will ignore the -exclude parameter if it is not of type string[].
If I check the type returned by the above command, I get System.Object[]. I expect it to be System.String[] or just plain String[].
How do I convert the output of the above command to a string array?
The full command using copy-item, for clarity, is:
Copy-Item -Path (Join-Path $src "*") -Destination $dest -Recurse -Force -Exclude $((Get-ChildItem -Path $Dest -Recurse -File).FullName.TrimStart($Dest))
My end goal is to copy files recursively without overwriting existing files.

Answer 1

To get a string[] from the names of get-childitem cmdlet use the following
[string[]]$files = (Get-ChildItem).Name

Answer 2

This will do what it appears you say that you want? But, I think that may not be everything to your question.
$((Get-ChildItem -Path $Dest -Recurse -File).FullName.Replace("$Dest",'.'))

Answer 3

#mklement0 is right, -Exclude and -Include support file name patterns (i.e. "*.txt") and not an array of explicit paths.
This sounds like an awful lot like an XY Problem ;-)
If you simply want to copy files recursively without overwriting them, use Robocopy with the Mirror switch. e.g.:
robocopy C:/Source C:/Dest /mir
EDIT:
By default Copy-Item will always overwrite the files on copy, and there is no switches to get around this. I usually recommend Robocopy as it really simplifies things like this and is very "robust" and reliable.
If your requirements are for a "pure" PowerShell version, then you have to break the scrip out into two parts, 1. Get a list of all the files 2. Iterate through the filer and test to see if they are already in the destination before copying.
$SrcPath = "C:/Source"
$DestPath = "C:/Dest"
$SrcFiles = Get-ChildItem $SrcPath -Recurse
#Iterate through files testing:
$SrcFiles | ForEach-Object {
#Calculate Destination File/Folder name/path
$DestObj = $_.FullName.Replace($SrcPath, $DestPath)
if(Test-Path -LiteralPath $DestObj)
{
#File already Exists
Write-Host "File already Exists: $DestObj"
}
else
{
#File Does not exist - Copy
Write-Host "File Does not Exist Copy: $DestObj"
Copy-Item -Path $_ -Destination $DestObj
}
}