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

Answer 1

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.