Add a derived property to powershell command pipe - powershell

Question

If e.g. Get-NetTCPConnection command returns OwningProcess ID is it possible to create a one-liner which adds another columns which expands the ID to ProcessName as returned by Get-Process -Id?

Answer 1

Yes, using calculated expressions. See example 10 on the Select-Object documentation
Get-NetTCPConnection | select OwningProcess,#{n="ProcessName";e={Get-Process -Id $_.OwningProcess | select -ExpandProperty ProcessName}}
Edit
Is there a way to tell Select-Object to keep all properties without explicitly listing them so that the calculated expression appears in addition to what is printed by default?
Yes but it's a a lot more convoluted than it should be. The crux of it is (as you may already know) "all properties" and "printed by default" are two different things. You can see this by comparing Get-NetTCPConnection to Get-NetTCPConnection | select *
So to get all properties + the calculated property it would be:
Get-NetTCPConnection | select *,#{n="ProcessName";e={Get-Process -Id $_.OwningProcess | select -Expand ProcessName}}
To get the default properties + the calculated property (*sigh*):
# this is from Get-NetTCPConnection | Get-Member
$typeName = 'Microsoft.Management.Infrastructure.CimInstance#ROOT/StandardCimv2/MSFT_NetTCPConnection'
# export format data for this type
Get-FormatData -TypeName $typeName | Export-FormatData -IncludeScriptBlock -Path $env:TEMP\formatdata.ps1xml
# open the ps1xml in editor of choice C:\Users\<user>\AppData\Local\Temp\formatdata.ps1xml
# Add under TableHeaders
<TableColumnHeader>
<Width>14</Width>
</TableColumnHeader>
# Add under TableColumnItems
<TableColumnItem>
<ScriptBlock>
Get-Process -Id $_.OwningProcess | select -ExpandProperty ProcessName
</ScriptBlock>
</TableColumnItem>
# save ps1xml
# update format data
Update-FormatData -PrependPath $env:TEMP\formatdata.ps1xml
The above is limited to the current session. You can add Update-FormatData to your profile so it's done every time you start a session. Or use the scorched Earth approach and modify the source format file (not recommended, I didn't try it) located at C:\Windows\system32\WindowsPowerShell\v1.0\Modules\NetTCPIP\Tcpip.Format.ps1xml.
How to find this location:
Get-Command Get-NetTCPConnection | select -Expand Module | select -Expand ExportedFormatFiles
Related: Using the PowerShell formatting system to your advantage, about_format.ps1xml, Loading and Exporting Formatting Data, Get-FormatData, Update-FormatData