Using Cached Port File

In the previous tip we explained how you can download port assignments via PowerShell from IANA. This process requires Internet access and can take a while. So here is code that looks for a cached CSV file. If it is present, port data is loaded from file offline, else the data is retrieved online, and a cache file is written. Note especially how Tee-Object is used to create the cache file:

$url = 'https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv'
$CSVFile = "$env:temp\ports.csv"
$exists = Test-Path -Path $CSVFile

if (!$exists)
{
  Write-Warning "Retrieving data online..."

  $portinfo = Invoke-WebRequest -Uri $Url -UseBasicParsing | `
    Select-Object -ExpandProperty Content | `
    Tee-Object -FilePath $CSVFile | ConvertFrom-Csv
}
else
{
  Write-Warning "Loading cached file..."
  $portinfo = Import-Csv -Path $CSVFile
}

$portinfo | Out-GridView

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