Category Archives: Powershell

Implicit Foreach in PSv3

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PowerTip of the Day, from PowerShell.com:

PowerShell v3 Beta is available for quite some time now, so every now and then we start tossing in some PowerShell v3 tips. We’ll clearly mark them as such since they only run on PowerShell v3, not v2. This is something new in PowerShell v3:

When you work with array data, in previous PowerShell versions you had to loop through all elements to get to their properties and methods. No more in PowerShell v3. PowerShell now detects that you are working with an array and applies your call to all array elements. So with this line you could gracefully close all running notepad.exe.

(Get-Process notepad).CloseMainWindow()

Previously, you would have had to write:

Get-Process notepad | ForEach-Object { $_.CloseMainWindow() }

Export-CSV with append

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function Export-CSV {
[CmdletBinding(DefaultParameterSetName='Delimiter',
  SupportsShouldProcess=$true, ConfirmImpact='Medium')]
param(
 [Parameter(Mandatory=$true, ValueFromPipeline=$true,
           ValueFromPipelineByPropertyName=$true)]
 [System.Management.Automation.PSObject]
 ${InputObject},
 [Parameter(Mandatory=$true, Position=0)]
 [Alias('PSPath')]
 [System.String]
 ${Path},

 #region -Append (added by Dmitry Sotnikov)
 [Switch]
 ${Append},
 #endregion 
 [Switch]
 ${Force},
 [Switch]
 ${NoClobber},
 [ValidateSet('Unicode','UTF7','UTF8','ASCII','UTF32',
                  'BigEndianUnicode','Default','OEM')]
 [System.String]
 ${Encoding},
 [Parameter(ParameterSetName='Delimiter', Position=1)]
 [ValidateNotNull()]
 [System.Char]
 ${Delimiter},
 [Parameter(ParameterSetName='UseCulture')]
 [Switch]
 ${UseCulture},
 [Alias('NTI')]
 [Switch]
 ${NoTypeInformation})
begin
{
 # This variable will tell us whether we actually need to append
 # to existing file
 $AppendMode = $false

 try {
  $outBuffer = $null
  if ($PSBoundParameters.TryGetValue('OutBuffer', [ref]$outBuffer))
  {
      $PSBoundParameters['OutBuffer'] = 1
  }
  $wrappedCmd = $ExecutionContext.InvokeCommand.GetCommand('Export-Csv',
    [System.Management.Automation.CommandTypes]::Cmdlet)

 #String variable to become the target command line
 $scriptCmdPipeline = ''
 # Add new parameter handling
 #region Dmitry: Process and remove the Append parameter if it is present
 if ($Append) {

  $PSBoundParameters.Remove('Append') | Out-Null

  if ($Path) {
   if (Test-Path $Path) {        
    # Need to construct new command line
    $AppendMode = $true

    if ($Encoding.Length -eq 0) {
     # ASCII is default encoding for Export-CSV
     $Encoding = 'ASCII'
    }

    # For Append we use ConvertTo-CSV instead of Export
    $scriptCmdPipeline += 'ConvertTo-Csv -NoTypeInformation '

    # Inherit other CSV convertion parameters
    if ( $UseCulture ) {
     $scriptCmdPipeline += ' -UseCulture '
    }
    if ( $Delimiter ) {
     $scriptCmdPipeline += " -Delimiter '$Delimiter' "
    } 

    # Skip the first line (the one with the property names) 
    $scriptCmdPipeline += ' | Foreach-Object {$start=$true}'
    $scriptCmdPipeline += '{if ($start) {$start=$false} else {$_}} '

    # Add file output
    $scriptCmdPipeline += " | Out-File -FilePath '$Path'"
    $scriptCmdPipeline += " -Encoding '$Encoding' -Append "

    if ($Force) {
     $scriptCmdPipeline += ' -Force'
    }
    if ($NoClobber) {
     $scriptCmdPipeline += ' -NoClobber'
    }   
   }
  }
 } 

 $scriptCmd = {& $wrappedCmd @PSBoundParameters }

 if ( $AppendMode ) {
  # redefine command line
  $scriptCmd = $ExecutionContext.InvokeCommand.NewScriptBlock(
      $scriptCmdPipeline
    )
 } else {
  # execute Export-CSV as we got it because
  # either -Append is missing or file does not exist
  $scriptCmd = $ExecutionContext.InvokeCommand.NewScriptBlock(
      [string]$scriptCmd
    )
 }
 # standard pipeline initialization
 $steppablePipeline = $scriptCmd.GetSteppablePipeline(
        $myInvocation.CommandOrigin)
 $steppablePipeline.Begin($PSCmdlet)

 } catch {
   throw
 }

}
process
{
  try {
      $steppablePipeline.Process($_)
  } catch {
      throw
  }
}
end
{
  try {
      $steppablePipeline.End()
  } catch {
      throw
  }
}

}