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Pipeline input

As explained in Learn PowerShell Scripting in a Month of Lunches, Second Edition: Write and organize scripts and tools

Pipeline input is data supplied to a PowerShell command by a preceding pipeline command.

Pipeline input is data supplied to a PowerShell command by a preceding pipeline command. Designing functions to accept it lets commands work independently or as reusable stages in larger automation tasks. section 4.5 section 17.1.3

A function accepts pipeline input through parameter-binding attributes and processes objects in pipeline-aware stages:

  • Use ValueFromPipeline for ByValue binding. A string parameter such as $ComputerName can receive each incoming string object. section 11.1.1
  • Use ValueFromPipelineByPropertyName when incoming objects are not strings but expose a matching property, such as ComputerName. section 11.1.1
  • Put per-object work in PROCESS{}. PowerShell runs it as each pipeline value is bound, then runs END{} after all objects have passed through. section 11.1.1
  • Design the function for both direct parameter use and pipeline use; the extra parameter and processing structure prevent a tool from being locked to one calling style. section 11.1.1 section 27.2

Passing computer names through a function

Direct invocation supplies multiple values as a parameter: Get-MachineInfo -ComputerName ONE,TWO,THREE. Pipeline invocation supplies them one at a time: "ONE","TWO","THREE" | Get-MachineInfo. With [Parameter(ValueFromPipeline=$True)] on $ComputerName, PROCESS{} runs for each computer, while END{} can perform final work such as writing "All Done". section 11.1.1

Listing 11.1 Original Get-MachineInfo function
function Get-MachineInfo {
    Param(
        [string[]]$ComputerName,
        [string]$LogFailuresToPath,
        [string]$Protocol = "Wsman",
        [switch]$ProtocolFallback
    )
    foreach ($computer in $computername) {
        if ($protocol -eq 'Dcom') {                                    #1
            $option = New-CimSessionOption -Protocol Dcom
        } else {
            $option = New-CimSessionOption -Protocol Wsman
        }
        $session = New-CimSession -ComputerName $computer              #2
        -SessionOption $option
        # 
        $os = Get-CimInstance -ClassName Win32_OperatingSystem         #3
         -CimSession $session
        $session | Remove-CimSession                                   #4
        $os | Select-Object -Prop @{n='ComputerName';e={$computer}},   #5
                                Version,ServicePackMajorVersion
    } #foreach
} #function
#1 Establishes session protocol
#2 Connects the session
#3 Queries data
#4 Closes the session
#5 Outputs the data

Compare the original Get-MachineInfo function with a pipeline-enabled design, then adapt its focused connection, query, cleanup, and output steps. section 17.1.3

How Learn PowerShell Scripting in a Month of Lunches, Second Edition: Write and organize scripts and tools covers it

How deep it goes
Explains ByValue and ByPropertyName binding plus BEGIN, PROCESS, and END execution, without detailing binding internals.
Examples
Demonstrates Get-MachineInfo with direct computer-name arguments, piped strings, matching properties, and an END-block completion message.
What you can do after
Build it from scratch by adding pipeline-binding attributes and PROCESS logic to focused PowerShell functions.
How it connects
Connects pipeline input with parameter binding, advanced functions, PowerShell pipeline composition, and modular function design.
Cover of Learn PowerShell Scripting in a Month of Lunches, Second Edition: Write and organize scripts and tools
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Related concepts

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