https://powershell.org/forums/topic/exception-handling-question/

ExceptionHandling.ps1

# Process the groups
$OUs | ForEach-Object {
    # Build the old group name
    $OldGroup = "DtaG_Student_${_}_1Fa"

    # Build the new group name
    $NewGroup = "DtaG_Student_${_}_190901Fa-"
    
    try {
        # Get group members
        $Members = Get-ADGroupMember $OldGroup

        # Make sure last year's students aren't still in the old group
        Remove-ADGroupMember $Oldgroup -Members $Members -whatif

        # Add the new group to the old group
        Add-ADGroupMember $OldGroup -Members $NewGroup -whatif
    }
    catch [Microsoft.ActiveDirectory.Management.ADIdentityNotFoundException] {
        $NoGroup += $OldGroup
        Write-Error "$OldGroup NOT FOUND"
        # if the old group was one of the TEP groups, change the Old Group format to DtaG_Student_TEP_$OU_1Fa, 
        # then remove existing members, add the new group before looping to the next OU
    }
    catch {
        # Log additional errors, and either rethrow the error or pass it to Write-Error
        # depending on whether you want execution to terminate or keep going through the
        # rest of your OUs.
        
        # Rethrow (terminate execution) options:
        # 1. $PSCmdlet.ThrowTerminatingError($_)
        # 2. throw $_
        # 3. $_ | Write-Error -ErrorAction Stop
        
        # Otherwise just write-error:
        # $_ | Write-Error
    }
}