Piping between functions

A question came up about piping between advanced functions. The input to the second function might be an array. To illustrate how this works imagine a function that gets disk information – or better still use this one.

function get-mydisk{
[CmdletBinding()]
param (
   [string]$computername="$env:COMPUTERNAME"
)
BEGIN{}#begin 
PROCESS{
Get-WmiObject -Class Win32_LogicalDisk -ComputerName $computername |
foreach {
New-Object -TypeName PSObject -Property @{
 Disk = $_.DeviceID
 Free = $_.FreeSpace
 Size = $_.Size
}
}
}#process 
END{}#end
}

Use a computername as a parameter. Use WMI to get the disk information and output an object.

PS> get-mydisk | ft -AutoSize

Disk         Free         Size
—-         —-         —-
C:   149778239488 249951154176
D:       69271552    104853504
E:                           
F:                           

This works as well

PS> get-mydisk | where Size -gt 0 | ft -AutoSize

Disk         Free         Size
—-         —-         —-
C:   149778108416 249951154176
D:       69271552    104853504

You now have a function outputs objects that behave properly on the pipeline.

So now you want those objects piped into another function or you want an array of objects used as the input

function get-freeperc {
[CmdletBinding()]
param (
[parameter(ValueFromPipeline=$true)]
  [Object[]]$disklist
)
BEGIN{}#begin 
PROCESS{
foreach ($disk in $disklist){
 if ($disk.Size -gt 0){
   $disk | Select Disk,
   @{N="Size(GB)"; E={[math]::Round( ($($_.Size)/1GB), 2 )}},
   @{N="FreePerc"; E={[math]::Round( ($($_.Free) / $($_.Size))*100, 2 )}}
 }
}
}#process 
END{}#end
}

• Set the parameter to accept pipeline input
• Set the parameter to accept an array of objects
• Use a process block
• Use a foreach block in the process block

This works

PS> get-mydisk | get-freeperc | ft -AutoSize

Disk Size(GB) FreePerc
—- ——– ——–
C:     232.79    59.92
D:        0.1    66.07

or this

$disks = get-mydisk
get-freeperc -disklist $disks

or this

get-freeperc -disklist (get-mydisk)