How to capture value from a PS expression?

Question

I'm trying to put together an expression that returns a bare value, without a table or name of the expression included.

For example, I have this line from another solution:

gwmi win32_logicaldisk -Filter "DeviceID = 'C:'" |
  Format-Table @{n="Size";e={[math]::Round($_.Size/1GB,2)}}

This returns:

 Size
 ----
475.33

How can I grab just the 475.33?

`gwmi win32_logicaldisk -Filter "DeviceID = 'C:'" | Select-Object -Property @{n="Size";e={[math]::Round($_.Size/1GB,2)}} | Select-Object -ExpandProperty Size` — Olaf, Jan 30 '20 at 23:18

score 0 · Answer 1 · answered Jan 30 '20 at 23:16

0

Use Select-Object instead of Format-Table:

$DiskC = gwmi win32_logicaldisk -Filter "DeviceID = 'C:'" | Select-Object @{n="Size";e={[math]::Round($_.Size/1GB,2)}}

$DiskC.Size

answered Jan 30 '20 at 23:16

Mathias R. Jessen

score 0 · Answer 2 · answered Jan 31 '20 at 00:03

Format-* cmdlets return objects whose sole purpose is to provide formatting instructions to PowerShell's output-formatting system - see this answer. In short: only ever use Format-* cmdlets to format data for display, never for subsequent programmatic processing.
gwmi is the built-in alias for the Get-WmiObject cmdlet, which is obsolete. The CIM cmdlets (e.g., Get-CimInstance) superseded the WMI cmdlets in PowerShell v3 (released in September 2012). Therefore, the WMI cmdlets should be avoided, not least because PowerShell [Core] v6+, where all future effort will go, doesn't even have them anymore. For more information, see this answer.
If you simply want to calculate a value derived from (each of) your input object(s), use the ForEach-Object cmdlet.

Therefore:

Get-CimInstance win32_logicaldisk -Filter "DeviceID = 'C:'" | ForEach-Object {
  [math]::Round($_.Size / 1gb, 2)
}

Or, more simply, using an expression:

[math]::Round(
  (Get-CimInstance win32_logicaldisk -Filter "DeviceID = 'C:'").Size / 1gb, 2
)

score 0 · Answer 3 · answered Jan 31 '20 at 13:51

If you use your first line:

gwmi win32_logicaldisk -Filter "DeviceID = 'C:'" | Format-Table @{n="Size";e={[math]::Round($_.Size/1GB,2)}}

But Pipe it trough Select-object instead of format table then pipe it again to select object expanding the property (or just .size)

  gwmi win32_logicaldisk -Filter "DeviceID = 'C:'" | Select @{n="Size";e={[math]::Round($_.Size/1GB,2)}} | select -ExpandProperty Size

3 Answers3