How do you write a powershell function that reads from piped input?

Question

SOLVED:

The following are the simplest possible examples of functions/scripts that use piped input. Each behaves the same as piping to the "echo" cmdlet.

As functions:

Function Echo-Pipe {
  Begin {
    # Executes once before first item in pipeline is processed
  }

  Process {
    # Executes once for each pipeline object
    echo $_
  }

  End {
    # Executes once after last pipeline object is processed
  }
}

Function Echo-Pipe2 {
    foreach ($i in $input) {
        $i
    }
}

As Scripts:

# Echo-Pipe.ps1

  Begin {
    # Executes once before first item in pipeline is processed
  }

  Process {
    # Executes once for each pipeline object
    echo $_
  }

  End {
    # Executes once after last pipeline object is processed
  }

# Echo-Pipe2.ps1

foreach ($i in $input) {
    $i
}

E.g.

PS > . theFileThatContainsTheFunctions.ps1 # This includes the functions into your session
PS > echo "hello world" | Echo-Pipe
hello world
PS > cat aFileWithThreeTestLines.txt | Echo-Pipe2
The first test line
The second test line
The third test line

Please don't edit your questions to incorporate the solution, but mark it as solved by checking the tick next to the correct answer. — schuelermine
– schuelermine, Commented Apr 11, 2020 at 17:02
I know this question isn't asking for this, but if the people coming to this question want to process the whole pipe input rather than one item at a time, see this answer — WhiteKnight
– WhiteKnight, Commented Sep 26, 2024 at 13:04

Ruben Bartelink · Accepted Answer · 2014-11-14 08:38:45Z

17

You also have the option of using advanced functions, instead of the basic approach above:

function set-something { 
    param(
        [Parameter(ValueFromPipeline=$true)]
        $piped
    )

    # do something with $piped
}

It should be obvious that only one parameter can be bound directly to pipeline input. However, you can have multiple parameters bind to different properties on pipeline input:

function set-something { 
    param(
        [Parameter(ValueFromPipelineByPropertyName=$true)]
        $Prop1,

        [Parameter(ValueFromPipelineByPropertyName=$true)]
        $Prop2,
    )

    # do something with $prop1 and $prop2
}

Hope this helps you on your journey to learn another shell.

edited Nov 14, 2014 at 8:38

Ruben Bartelink

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answered Aug 31, 2012 at 15:32

x0n

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