PowerShell RoboCopy path issue - variables

Question

Objective: Robo copy from multiple machines on the network to a network share using variables for both the machine name and the currently logged on user.
What I have: txt file with a list of computernames.
Issue: I cannot get the foreach to work with the .split("\")[1] I use on the username variable to remove the domain prefix so I can use the output from that in the robocopy path
something like
robocopy "\\$computername\c$\documents and settings\$username\backup" "\\networkshare\backup\$username\backup"
gives me the error
You cannot call a method on a null-valued expression.
At C:\Scripts\Test\backup.ps1:13 char:2
Here's what I have so far. Can somebody help please?
function Get-LoggedIn {
[CmdletBinding()]
param (
[Parameter(Mandatory=$True)]
[string[]]$computername
)
foreach ($pc in $computername){
$logged_in = (gwmi win32_computersystem -COMPUTER $pc).username
$name = $logged_in.split("\")[1]
"{1}" -f $pc,$name
}
}
$computers = Get-Content "C:\Scripts\testcomputers.txt"
foreach ($computer in $computers) {
$users = Get-LoggedIn $computer
}
$SourceFolder = "\\$computer\c$\users\$users\desktop"
$DestinationFolder = "\\networkshare\backups\$users\backup\desktop"
$Logfile = "\\networkshare\backups\$users\backup\backuplog.txt"
Robocopy $SourceFolder $DestinationFolder /E /R:1 /W:1 /LOG:$Logfile

Answer 1

I see multiple errors here. You're not running the copy commands inside the foreach-loop. The username property recieved from WMI can often be in the following format:
domain\computer\username (or computer\domain\username, unsure since I'm on non-domain workstation now)
Anyways, the username is always the last part, so get it by using the index [-1] instead.
Updated script (with indents!):
function Get-LoggedIn {
[CmdletBinding()]
param (
[Parameter(Mandatory=$True)]
[string[]]$computername
)
foreach ($pc in $computername){
$logged_in = (gwmi win32_computersystem -COMPUTER $pc).username
$name = $logged_in.split("\")[-1]
"{1}" -f $pc,$name
}
}
$computers = Get-Content "C:\Scripts\testcomputers.txt"
foreach ($computer in $computers) {
$users = Get-LoggedIn $computer
$SourceFolder = "\\$computer\c$\users\$users\desktop"
$DestinationFolder = "\\networkshare\backups\$users\backup\desktop"
$Logfile = "\\networkshare\backups\$users\backup\backuplog.txt"
& Robocopy $SourceFolder $DestinationFolder /E /R:1 /W:1 /LOG:$Logfile
}