Export-CSV with append

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
  }
}

}
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