L3. Filtering, Exporting, and Working with CSV and JSON

Filtering Correctly

Filtering is where PowerShell becomes practical. Start with the most specific command possible, then use Where-Object when the command does not have a built-in filter.

Get-Service | Where-Object Status -eq 'Running'
Get-ChildItem -Path . -File | Where-Object Length -gt 1MB

When a cmdlet has a native filter, prefer it. For example, Get-ChildItem -Filter *.log lets the provider filter earlier than Where-Object Name -like '*.log'.

Export Without Losing Structure

Get-Process |
  Sort-Object CPU -Descending |
  Select-Object -First 20 Name, Id, CPU, WorkingSet |
  Export-Csv -Path .\top-processes.csv -NoTypeInformation
Import-Csv .\top-processes.csv | Sort-Object CPU -Descending

CSV is excellent for tables. JSON is better for nested objects and API payloads.

$payload = [pscustomobject]@{
  computer = $env:COMPUTERNAME
  time = (Get-Date).ToString('o')
  services = Get-Service | Where-Object Status -eq 'Running' | Select-Object -First 5 Name, Status
}
$payload | ConvertTo-Json -Depth 4 | Set-Content .\snapshot.json
Get-Content .\snapshot.json -Raw | ConvertFrom-Json

Calculated Properties

Calculated properties let you rename or transform data during selection:

Get-Process |
  Select-Object Name, Id, @{ Name = 'MemoryMB'; Expression = { [math]::Round($_.WorkingSet64 / 1MB, 2) } }

Lab

1. Export running services to CSV.
2. Import that CSV and sort by service name.
3. Create a JSON file with your hostname, current date, and PowerShell version.
4. Add one calculated property to convert bytes to MB.

Sources

• Microsoft Learn: Everything about hashtables