powershell use employeeID to get sAMAccount information

Question

I have a csv file with employee ID's, these ID's are tied to AD Accounts, I need to get the AD User information from the employee ID and export them to a csv file. Below is the script I wrote, it works if I run it without the export-csv switch, I have tried adding a pipe but the error I get from that is pipe cannot be empty.

    $userIDs = Import-CSV "C:\Users_.csv"
    foreach($userID in $userIDs)
    { 
    Get-ADUser -Filter "EmployeeID -eq $($userID.EmployeeID)" -Properties SAMAccountName 
    }

    Export-CSV "C:\UserResults.csv" -NoTypeInformation -Encoding UTF8

Solution

You can use a single pipeline:

Import-CSV "C:\Users_.csv" | 
  ForEach-Object { Get-ADUser -Filter "EmployeeID -eq $($_.EmployeeID)" } |
    Export-CSV "C:\UserResults.csv" -NoTypeInformation -Encoding UTF8

Note the use of the ForEach-Object cmdlet instead of the foreach statement - only the cmdlet can be used in a pipeline.
(Somewhat confusingly, the cmdlet has an alias also named foreach; whether the statement or the cmdlet is used is implied by the context (parsing mode).)

Inside the script block { ... } passed to ForEach-Object, automatic variable $_ represents the input object at hand.

Also note that Get-ADUser outputs objects that have property SAMAccountName by default, so you needn't request it explicitly.