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Explain ValueFromPipeline in PowerShell Advanced Functions
Consider the below example, we have created Advanced function to get the specific process information like Process Name, Process ID (PID), Start Time, Responding status, etc.
function Get-ProcessInformation{
[cmdletbinding()]
param(
[Parameter(Mandatory=$True)]
[string[]]$name
)
Begin{
Write-Verbose "Program started"
}
Process{
Write-Verbose "Extracting Process Inforamtion" Get-Process $name | Select Name, ID, StartTime, Responding | ft - AutoSize
}
End{
Write-Verbose "Function ends here"
}
}
Above is the advanced function example. When we run the above command, it will give us the Process information about the selected tables.
Output
PS C:\WINDOWS\system32> Get-ProcessInformation -name Chrome Name Id StartTime Responding ---- -- --------- ---------- chrome 1284 24-04-2020 21:29:25 True chrome 1316 24-04-2020 21:29:37 True chrome 2004 25-04-2020 17:12:40 True chrome 2676 26-04-2020 10:59:37 True chrome 3096 24-04-2020 23:39:00 True chrome 4660 25-04-2020 22:43:34 True chrome 6040 24-04-2020 21:29:31 True chrome 6548 26-04-2020 10:59:30 True chrome 6592 26-04-2020 10:59:39 True chrome 6644 25-04-2020 16:41:59 True chrome 6780 26-04-2020 09:53:33 True chrome 7392 25-04-2020 11:47:22 True chrome 10540 26-04-2020 10:56:49 True chrome 11288 24-04-2020 21:33:05 True chrome 12088 26-04-2020 10:59:48 True chrome 12100 24-04-2020 21:29:38 True chrome 13112 26-04-2020 10:59:48 True chrome 13460 26-04-2020 10:59:45 True
Now we will pass the above-created function as the pipeline output and check if it works?
PS C:\WINDOWS\system32> "Chrome" | Get-ProcessInformation cmdlet Get-ProcessInformation at command pipeline position 1 Supply values for the following parameters: name: Get-ProcessInformation : Cannot bind argument to parameter 'name' because it is an empty string. At line:1 char:12 + "Chrome" | Get-ProcessInformation + ~~~~~~~~~~~~~~~~~~~~~~ + CategoryInfo : InvalidData: (:) [Get-ProcessInformation], Param eterBindingValidationException + FullyQualifiedErrorId : ParameterArgumentValidationErrorEmptyStringNotAl lowed,Get-ProcessInformation
This doesn’t work because this function is not compatible to use as the Pipeline input. It doesn’t take the “chrome” as its input and asks for the value of the Name variable because of the Mandatory parameter. We simply need to add ValueFromPipeline() parameter. As we have already used the Mandatory parameter in the function so just need to add one more pipeline parameter as shown below.
function Get-ProcessInformation{
[cmdletbinding()]
param(
[Parameter(Mandatory=$True,ValuefromPipeline=$True)]
[string[]]$name
)
Begin{
Write-Verbose "Program started"
}
Process{
Write-Verbose "Extracting Process Inforamtion" Get-Process $name | Select Name, ID, StartTime, Responding | ft - AutoSize
}
End{
Write-Verbose "Function ends here"
}
}
Now, let's check if it works or not.
PS C:\WINDOWS\system32> "Chrome" | Get-ProcessInformation Name Id StartTime Responding ---- -- --------- ---------- chrome 1284 24-04-2020 21:29:25 True chrome 1316 24-04-2020 21:29:37 True chrome 2004 25-04-2020 17:12:40 True chrome 2676 26-04-2020 10:59:37 True chrome 3096 24-04-2020 23:39:00 True chrome 4660 25-04-2020 22:43:34 True chrome 6040 24-04-2020 21:29:31 True chrome 6548 26-04-2020 10:59:30 True chrome 6592 26-04-2020 10:59:39 True chrome 6644 25-04-2020 16:41:59 True chrome 6780 26-04-2020 09:53:33 True chrome 7392 25-04-2020 11:47:22 True chrome 10540 26-04-2020 10:56:49 True chrome 11288 24-04-2020 21:33:05 True chrome 12088 26-04-2020 10:59:48 True
Yes, it works. Now what if we provide the two existing process names as the input, it will not provide the desired result because the string we declared in the parameter section is not an array, it is a single string variable. We will declare it as the String array now.
function Get-ProcessInformation{
[cmdletbinding()]
param(
[Parameter(Mandatory=$True,ValuefromPipeline=$True)]
[string[]]$name
)
Begin{
Write-Verbose "Program started"
}
Process{
Write-Verbose "Extracting Process Inforamtion" Get-Process $name | Select Name, ID, StartTime, Responding | ft - AutoSize
}
End{
Write-Verbose "Function ends here"
}
}
Check the output now.
PS C:\WINDOWS\system32> "Chrome","SkypeApp" | Get-ProcessInformation Name Id StartTime Responding ---- -- --------- ---------- chrome 1284 24-04-2020 21:29:25 True chrome 1316 24-04-2020 21:29:37 True chrome 2004 25-04-2020 17:12:40 True chrome 2676 26-04-2020 10:59:37 True chrome 3096 24-04-2020 23:39:00 True chrome 4660 25-04-2020 22:43:34 True chrome 6040 24-04-2020 21:29:31 True chrome 6548 26-04-2020 10:59:30 True chrome 6592 26-04-2020 10:59:39 True chrome 6644 25-04-2020 16:41:59 True chrome 6780 26-04-2020 09:53:33 True Name Id StartTime Responding ---- -- --------- ---------- SkypeApp 2552 21-04-2020 18:31:02 True
Here, we are getting the desired output but for each new process, we are getting headers and we don’t need that. We need the combined output so we will use the foreach loop here and required to use PSCustomObject to gather the data.
function Get-ProcessInformation{
[cmdletbinding()]
param(
[Parameter(Mandatory=$True,ValuefromPipeline=$True)]
[string]$name
)
Begin{
Write-Verbose "Program started"
$out = @()
}
Process{
Write-Verbose "Extracting Process Inforamtion" $procs = Get-Process $name
foreach($proc in $procs){
$out += [PSCustomObject]@{
"Process_Name" = $proc.Name
"PID" = $proc.Id
"Start_Time" = $proc.StartTime
"Responding?" = $proc.Responding
}
}
}
End{
$out
Write-Verbose "Function ends here"
}
}
When you check the output above, the output is combined and as expected.
PS C:\WINDOWS\system32> "Chrome","SkypeApp" | Get-ProcessInformation Process_Name PID Start_Time Responding? ------------ --- ---------- ----------- chrome 1284 24-04-2020 21:29:25 True chrome 1316 24-04-2020 21:29:37 True chrome 2004 25-04-2020 17:12:40 True chrome 2676 26-04-2020 10:59:37 True chrome 3096 24-04-2020 23:39:00 True chrome 4660 25-04-2020 22:43:34 True chrome 6040 24-04-2020 21:29:31 True chrome 6548 26-04-2020 10:59:30 True chrome 6592 26-04-2020 10:59:39 True chrome 6644 25-04-2020 16:41:59 True chrome 6780 26-04-2020 09:53:33 True chrome 7392 25-04-2020 11:47:22 True chrome 10540 26-04-2020 10:56:49 True chrome 11288 24-04-2020 21:33:05 True chrome 12088 26-04-2020 10:59:48 True chrome 12100 24-04-2020 21:29:38 True SkypeApp 2552 21-04-2020 18:31:02 True
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