Loop through each item against a cmdlet - powershell

Question

I have a list of port number and I want to see which program is using that port. I want to filter the Get-Networkstatistics cmdlet to show me only certain ports that are in the port.txt file. I modified the
Get-NetworkStatistics | Select-Object ComputerName, LocalPort, ProcessName
to loop through only the port numbers I provide. However, the $result variable is not storing anything and the output is null. What am I doing wrong?
$file = .\ports.txt
foreach ( $port in $file )
{
$result += Get-NetworkStatistics |
Select-Object ComputerName, LocalPort, ProcessName |
Where-Object {$_.LocalPort -eq $port}
}
$result | Export-Csv .\networkports.csv

Answer 1

You have to use the Get-Content cmdlet:
$file = Get-Content "path_to_ports.txt'

Answer 2

First of all, you want to filter before doing Select, that way you have to select lower objects.
$result = #() #array
foreach ( $port in $file )
{
$result += Get-NetworkStatistics | Where-Object {$_.LocalPort -eq $port} | Select-Object ComputerName, LocalPort, ProcessName
}
$result | Export-Csv .\networkports.csv
As for the actual problem itself, I believe it is due to scoping. You need to declare variable before the loop, so it is available in the loop, and after the loop.

Answer 3

The statement
$file = .\ports.txt
Doesn't read the file into the variable. Use Get-Content for that.
Also, you don't need a loop. Get-Content reads the input file into an array of strings, so you can use the -contains operator for checking if the list contains a given local port:
$ports = Get-Content '.\ports.txt'
Get-NetworkStatistics |
Where-Object { $ports -contains $_.LocalPort } |
Select-Object ComputerName, LocalPort, ProcessName |
Export-Csv '.\networkports.csv' -NoType
On PowerShell v3 or newer you can also use the -in operator, which feels a bit more "natural" to most users:
$ports = Get-Content '.\ports.txt'
Get-NetworkStatistics |
Where-Object { $_.LocalPort -in $ports } |
Select-Object ComputerName, LocalPort, ProcessName |
Export-Csv '.\networkports.csv' -NoType