PowerShell's pipe adds linefeed

Question

I'm trying to pipe a string into a program's STDIN without any trailing linefeeds (unless that string itself actually ends in a linefeed). I tried googling around, but I only found people trying to print to the console without a trailing linefeed, in which case Write-Host takes a parameter -NoNewLine. However, to pipe it on to another program, I need Write-Output or similar which doesn't have such a parameter. Now it seems like Write-Output isn't even the problem:

Z:\> (Write-Output "abc").Length
3

But as soon as I pipe it to another program and read the string there, I get an additional linefeed. For instance, I tried this Ruby snippet:

Z:\> Write-Output "abc" | ruby -e "p ARGF.read"
"abc\n"

I checked that the actual string received is abc\n. The same happens in several other languages (at least C#, Java and Python), so I believe it's an issue with PowerShell, not the language doing the reading.

As a further test, I replaced Write-Output itself with another Ruby script:

Z:\> ruby -e "$> << 'abc'"
abcZ:\>

(That is, there is definitely no \n on the script's STDOUT.)

But again, when I pipe it into another script:

Z:\> ruby -e "$> << 'abc'" | ruby -e "p ARGF.read"
"abc\n"

I'm fairly convinced that it's the pipe which adds the linefeed. How do I avoid that? I actually want to be able to control whether the input ends in a linefeed or not (by including it in the input or omitting it).

(For reference, I also tested strings which already contain a trailing linefeed, and in that case the pipe doesn't add another one, so I guess it just ensures a trailing linefeed.)

I originally encountered this in PowerShell v3, but I'm now using v5 and still have the same issue.

Answer 1

Introduction

Here is my Invoke-RawPipeline function (get latest version from this Gist).

Use it to pipe binary data between processes' Standard Output and Standard Input streams. It can read input stream from file/pipeline and save resulting output stream to file.

It requires PsAsync module to be able to launch and pipe data in multiple processes.

In case of issues use -Verbose switch to see debug output.

Examples

Redirecting to file

• Batch:
  findstr.exe /C:"Warning" /I C:\Windows\WindowsUpdate.log > C:\WU_Warnings.txt
• PowerShell:
  Invoke-RawPipeline -Command @{Path = 'findstr.exe' ; Arguments = '/C:"Warning" /I C:\Windows\WindowsUpdate.log'} -OutFile 'C:\WU_Warnings.txt'

Redirecting from file

• Batch:
  svnadmin load < C:\RepoDumps\MyRepo.dump
• PowerShell:
  Invoke-RawPipeline -InFile 'C:\RepoDumps\MyRepo.dump' -Command @{Path = 'svnadmin.exe' ; Arguments = 'load'}

Piping strings

• Batch:
  echo TestString | find /I "test" > C:\SearchResult.log
• PowerShell:
  'TestString' | Invoke-RawPipeline -Command @{Path = 'find.exe' ; Arguments = '/I "test"'} -OutFile 'C:\SearchResult.log'

Piping between multiple processes

• Batch:
  ipconfig | findstr /C:"IPv4 Address" /I
• PowerShell:
  Invoke-RawPipeline -Command @{Path = 'ipconfig'}, @{Path = 'findstr' ; Arguments = '/C:"IPv4 Address" /I'} -RawData

Code:

<#
.Synopsis
    Pipe binary data between processes' Standard Output and Standard Input streams.
    Can read input stream from file and save resulting output stream to file.

.Description
    Pipe binary data between processes' Standard Output and Standard Input streams.
    Can read input stream from file/pipeline and save resulting output stream to file.
    Requires PsAsync module: http://psasync.codeplex.com

.Notes
    Author: beatcracker (https://beatcracker.wordpress.com, https://github.com/beatcracker)
    License: Microsoft Public License (http://opensource.org/licenses/MS-PL)

.Component
    Requires PsAsync module: http://psasync.codeplex.com

.Parameter Command
    An array of hashtables, each containing Command Name, Working Directory and Arguments

.Parameter InFile
    This parameter is optional.

    A string representing path to file, to read input stream from.

.Parameter OutFile
    This parameter is optional.

    A string representing path to file, to save resulting output stream to.

.Parameter Append
    This parameter is optional. Default is false.

    A switch controlling wheither ovewrite or append output file if it already exists. Default is to overwrite.

.Parameter IoTimeout
    This parameter is optional. Default is 0.

    A number of seconds to wait if Input/Output streams are blocked. Default is to wait indefinetely.

.Parameter ProcessTimeout
    This parameter is optional. Default is 0.

    A number of seconds to wait for process to exit after finishing all pipeline operations. Default is to wait indefinetely.
    Details: https://msdn.microsoft.com/en-us/library/ty0d8k56.aspx

.Parameter BufferSize
    This parameter is optional. Default is 4096.

    Size of buffer in bytes for read\write operations. Supports standard Powershell multipliers: KB, MB, GB, TB, and PB.
    Total number of buffers is: Command.Count * 2 + InFile + OutFile.

.Parameter ForceGC
    This parameter is optional.

    A switch, that if specified will force .Net garbage collection.
    Use to immediately release memory on function exit, if large buffer size was used.

.Parameter RawData
    This parameter is optional.

    By default function returns object with StdOut/StdErr streams and process' exit codes.
    If this switch is specified, function will return raw Standard Output stream.

.Example
    Invoke-RawPipeline -Command @{Path = 'findstr.exe' ; Arguments = '/C:"Warning" /I C:\Windows\WindowsUpdate.log'} -OutFile 'C:\WU_Warnings.txt'

    Batch analog: findstr.exe /C:"Warning" /I C:\Windows\WindowsUpdate.log' > C:\WU_Warnings.txt

.Example
    Invoke-RawPipeline -Command @{Path = 'findstr.exe' ; WorkingDirectory = 'C:\Windows' ; Arguments = '/C:"Warning" /I .\WindowsUpdate.log'} -RawData

    Batch analog: cd /D C:\Windows && findstr.exe /C:"Warning" /I .\WindowsUpdate.log

.Example
    'TestString' | Invoke-RawPipeline -Command @{Path = 'find.exe' ; Arguments = '/I "test"'} -OutFile 'C:\SearchResult.log'

    Batch analog: echo TestString | find /I "test" > C:\SearchResult.log

.Example
    Invoke-RawPipeline -Command @{Path = 'ipconfig'}, @{Path = 'findstr' ; Arguments = '/C:"IPv4 Address" /I'} -RawData

    Batch analog: ipconfig | findstr /C:"IPv4 Address" /I

.Example
    Invoke-RawPipeline -InFile 'C:\RepoDumps\Repo.svn' -Command @{Path = 'svnadmin.exe' ; Arguments = 'load'}

    Batch analog: svnadmin load < C:\RepoDumps\MyRepo.dump
#>

function Invoke-RawPipeline
{
    [CmdletBinding()]
    Param
    (
        [Parameter(ValueFromPipeline = $true)]
        [ValidateNotNullOrEmpty()]
        [ValidateScript({
            if($_.psobject.Methods.Match.('ToString'))
            {
                $true
            }
            else
            {
                throw 'Can''t convert pipeline object to string!'
            }
        })]
        $InVariable,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [ValidateScript({
            $_ | ForEach-Object {
                $Path = $_.Path
                $WorkingDirectory = $_.WorkingDirectory

                if(!(Get-Command -Name $Path -CommandType Application -ErrorAction SilentlyContinue))
                {
                    throw "Command not found: $Path"
                }

                if($WorkingDirectory)
                {
                    if(!(Test-Path -LiteralPath $WorkingDirectory -PathType Container -ErrorAction SilentlyContinue))
                    {
                        throw "Working directory not found: $WorkingDirectory"
                    }
                }
            }
            $true
        })]
        [ValidateNotNullOrEmpty()]
        [array]$Command,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [ValidateScript({
            if(!(Test-Path -LiteralPath $_))
            {
                throw "File not found: $_"
            }
            $true
        })]
        [ValidateNotNullOrEmpty()]
        [string]$InFile,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [ValidateScript({
            if(!(Test-Path -LiteralPath (Split-Path $_)))
            {
                throw "Folder not found: $_"
            }
            $true
        })]
        [ValidateNotNullOrEmpty()]
        [string]$OutFile,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [switch]$Append,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [ValidateRange(0, 2147483)]
        [int]$IoTimeout = 0,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [ValidateRange(0, 2147483)]
        [int]$ProcessTimeout = 0,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [long]$BufferSize = 4096,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [switch]$RawData,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [switch]$ForceGC
    )

    Begin
    {

        $Modules = @{PsAsync = 'http://psasync.codeplex.com'}

        'Loading modules:', ($Modules | Format-Table -HideTableHeaders -AutoSize | Out-String) | Write-Verbose

        foreach($module in $Modules.GetEnumerator())
        {
            if(!(Get-Module -Name $module.Key))
            {
                Try
                { 
                    Import-Module -Name $module.Key -ErrorAction Stop
                }
                Catch
                {
                    throw "$($module.Key) module not available. Get it here: $($module.Value)"
                }
            }
        }

        function New-ConsoleProcess
        {
            Param
            (
                [string]$Path,
                [string]$Arguments,
                [string]$WorkingDirectory,
                [switch]$CreateNoWindow = $true,
                [switch]$RedirectStdIn = $true,
                [switch]$RedirectStdOut = $true,
                [switch]$RedirectStdErr = $true
            )

            if(!$WorkingDirectory)
            {
                if(!$script:MyInvocation.MyCommand.Path)
                {
                    $WorkingDirectory = [System.AppDomain]::CurrentDomain.BaseDirectory
                }
                else
                {
                    $WorkingDirectory = Split-Path $script:MyInvocation.MyCommand.Path
                }
            }

            Try
            {
                $ps = New-Object -TypeName System.Diagnostics.Process -ErrorAction Stop
                $ps.StartInfo.Filename = $Path
                $ps.StartInfo.Arguments = $Arguments
                $ps.StartInfo.UseShellExecute = $false
                $ps.StartInfo.RedirectStandardInput = $RedirectStdIn
                $ps.StartInfo.RedirectStandardOutput = $RedirectStdOut
                $ps.StartInfo.RedirectStandardError = $RedirectStdErr
                $ps.StartInfo.CreateNoWindow = $CreateNoWindow
                $ps.StartInfo.WorkingDirectory = $WorkingDirectory
            }
            Catch
            {
                throw $_
            }

            return $ps
        }

        function Invoke-GarbageCollection
        {
            [gc]::Collect()
            [gc]::WaitForPendingFinalizers()
        }

        $CleanUp = {
            $IoWorkers + $StdErrWorkers |
            ForEach-Object {
                $_.Src, $_.Dst |
                ForEach-Object {
                    if(!($_ -is [System.Diagnostics.Process]))
                    {
                        Try
                        {
                            $_.Close()
                        }
                        Catch
                        {
                            Write-Error "Failed to close $_"
                        }
                        $_.Dispose()
                    }

                }
            }
        }

        $PumpData = {
            Param
            (
                [hashtable]$Cfg
            )
            # Fail hard, we don't want stuck threads
            $Private:ErrorActionPreference = 'Stop'

            $Src = $Cfg.Src
            $SrcEndpoint = $Cfg.SrcEndpoint
            $Dst = $Cfg.Dst
            $DstEndpoint = $Cfg.DstEndpoint
            $BufferSize = $Cfg.BufferSize
            $SyncHash = $Cfg.SyncHash
            $RunspaceId = $Cfg.Id
        
            # Setup Input and Output streams
            if($Src -is [System.Diagnostics.Process])
            {
                switch ($SrcEndpoint)
                {
                    'StdOut' {$InStream = $Src.StandardOutput.BaseStream}
                    'StdIn' {$InStream = $Src.StandardInput.BaseStream}
                    'StdErr' {$InStream = $Src.StandardError.BaseStream}
                    default {throw "Not valid source endpoint: $_"}
                }
            }
            else
            {
                $InStream = $Src
            }

            if($Dst -is [System.Diagnostics.Process])
            {
                switch ($DstEndpoint)
                {
                    'StdOut' {$OutStream = $Dst.StandardOutput.BaseStream}
                    'StdIn' {$OutStream = $Dst.StandardInput.BaseStream}
                    'StdErr' {$OutStream = $Dst.StandardError.BaseStream}
                    default {throw "Not valid destination endpoint: $_"}
                }
            }            
            else
            {
                $OutStream = $Dst
            }

            $InStream | Out-String | ForEach-Object {$SyncHash.$RunspaceId.Status += "InStream: $_"}
            $OutStream | Out-String | ForEach-Object {$SyncHash.$RunspaceId.Status += "OutStream: $_"}

            # Main data copy loop
            $Buffer = New-Object -TypeName byte[] $BufferSize
            $BytesThru = 0

            Try
            {
                Do
                {
                    $SyncHash.$RunspaceId.IoStartTime = [DateTime]::UtcNow.Ticks
                    $ReadCount = $InStream.Read($Buffer, 0, $Buffer.Length)
                    $OutStream.Write($Buffer, 0, $ReadCount)
                    $OutStream.Flush()
                    $BytesThru += $ReadCount
                }
                While($readCount -gt 0)
            }
            Catch
            {
                $SyncHash.$RunspaceId.Status += $_
        
            }
            Finally
            {
                $OutStream.Close()
                $InStream.Close()
            }
        }
    }

    Process
    {
        $PsCommand = @()
        if($Command.Length)
        {
            Write-Verbose 'Creating new process objects'
            $i = 0
            foreach($cmd in $Command.GetEnumerator())
            {
                $PsCommand += New-ConsoleProcess @cmd
                $i++
            }
        }

        Write-Verbose 'Building I\O pipeline'
        $PipeLine = @()
        if($InVariable)
        {
                [Byte[]]$InVarBytes = [Text.Encoding]::UTF8.GetBytes($InVariable.ToString())
                $PipeLine += New-Object -TypeName System.IO.MemoryStream -ArgumentList $BufferSize -ErrorAction Stop
                $PipeLine[-1].Write($InVarBytes, 0, $InVarBytes.Length)
                [Void]$PipeLine[-1].Seek(0, 'Begin')
        }
        elseif($InFile)
        {
            $PipeLine += New-Object -TypeName System.IO.FileStream -ArgumentList ($InFile, [IO.FileMode]::Open) -ErrorAction Stop
            if($PsCommand.Length)
            {
                $PsCommand[0].StartInfo.RedirectStandardInput = $true
            }
        }
        else
        {
            if($PsCommand.Length)
            {
                $PsCommand[0].StartInfo.RedirectStandardInput = $false
            }
        }

        $PipeLine += $PsCommand

        if($OutFile)
        {
            if($PsCommand.Length)
            {
                $PsCommand[-1].StartInfo.RedirectStandardOutput = $true
            }

            if($Append)
            {
                $FileMode = [System.IO.FileMode]::Append
            }
            else
            {
                $FileMode = [System.IO.FileMode]::Create
            }

            $PipeLine += New-Object -TypeName System.IO.FileStream -ArgumentList ($OutFile, $FileMode, [System.IO.FileAccess]::Write) -ErrorAction Stop
        }
        else
        {
            if($PsCommand.Length)
            {
                $PipeLine += New-Object -TypeName System.IO.MemoryStream -ArgumentList $BufferSize -ErrorAction Stop
            }
        }
    
        Write-Verbose 'Creating I\O threads'
        $IoWorkers = @()
        for($i=0 ; $i -lt ($PipeLine.Length-1) ; $i++)
        {
            $SrcEndpoint = $DstEndpoint = $null
            if($PipeLine[$i] -is [System.Diagnostics.Process])
            {
                $SrcEndpoint = 'StdOut'
            }
            if($PipeLine[$i+1] -is [System.Diagnostics.Process])
            {
                $DstEndpoint = 'StdIn'
            }

            $IoWorkers += @{
                Src = $PipeLine[$i]
                SrcEndpoint = $SrcEndpoint
                Dst = $PipeLine[$i+1]
                DstEndpoint = $DstEndpoint
            }
        }
        Write-Verbose "Created $($IoWorkers.Length) I\O worker objects"

        Write-Verbose 'Creating StdErr readers'
        $StdErrWorkers = @()
        for($i=0 ; $i -lt $PsCommand.Length ; $i++)
        {
            $StdErrWorkers += @{
                Src = $PsCommand[$i]
                SrcEndpoint = 'StdErr'
                Dst = New-Object -TypeName System.IO.MemoryStream -ArgumentList $BufferSize -ErrorAction Stop
            }
        }
        Write-Verbose "Created $($StdErrWorkers.Length) StdErr reader objects"

        Write-Verbose 'Starting processes'
        $PsCommand |
            ForEach-Object {
                $ps = $_
                Try
                {
                    [void]$ps.Start()
                }
                Catch
                {
                    Write-Error "Failed to start process: $($ps.StartInfo.FileName)"
                    Write-Verbose "Can't launch process, killing and disposing all"

                    if($PsCommand)
                    {
                        $PsCommand |
                            ForEach-Object {
                                Try{$_.Kill()}Catch{} # Can't do much if kill fails...
                                $_.Dispose()
                            }
                    }

                        Write-Verbose 'Closing and disposing I\O streams'
                    . $CleanUp
                }
                Write-Verbose "Started new process: Name=$($ps.Name), Id=$($ps.Id)"
            }

        $WorkersCount = $IoWorkers.Length + $StdErrWorkers.Length
        Write-Verbose 'Creating sync hashtable'
        $sync = @{}
        for($i=0 ; $i -lt $WorkersCount ; $i++)
        {
            $sync += @{$i = @{IoStartTime = $nul ; Status = $null}}
        }
        $SyncHash = [hashtable]::Synchronized($sync)

        Write-Verbose 'Creating runspace pool'
        $RunspacePool = Get-RunspacePool $WorkersCount

        Write-Verbose 'Loading workers on the runspace pool'
        $AsyncPipelines = @()
        $i = 0
        $IoWorkers + $StdErrWorkers |
        ForEach-Object {
            $Param = @{
                BufferSize = $BufferSize
                Id = $i
                SyncHash = $SyncHash
            } + $_

            $AsyncPipelines += Invoke-Async -RunspacePool $RunspacePool -ScriptBlock $PumpData -Parameters $Param
            $i++

            Write-Verbose 'Started working thread'
            $Param | Format-Table -HideTableHeaders -AutoSize | Out-String | Write-Debug
        }

        Write-Verbose 'Waiting for I\O to complete...'
        if($IoTimeout){Write-Verbose "Timeout is $IoTimeout seconds"}

        Do
        {
            # Check for pipelines with errors
            [array]$FailedPipelines = Receive-AsyncStatus -Pipelines $AsyncPipelines | Where-Object {$_.Completed -and $_.Error}
            if($FailedPipelines)
            {
                "$($FailedPipelines.Length) pipeline(s) failed!",
                ($FailedPipelines | Select-Object -ExpandProperty Error | Format-Table -AutoSize | Out-String) | Write-Debug
            }

            if($IoTimeout)
            {
                # Compare I\O start time of thread with current time
                [array]$LockedReaders = $SyncHash.Keys | Where-Object {[TimeSpan]::FromTicks([DateTime]::UtcNow.Ticks - $SyncHash.$_.IoStartTime).TotalSeconds -gt $IoTimeout}
                if($LockedReaders)
                {
                    # Yikes, someone is stuck
                    "$($LockedReaders.Length) I\O operations reached timeout!" | Write-Verbose
                    $SyncHash.GetEnumerator() | ForEach-Object {"$($_.Key) = $($_.Value.Status)"} | Sort-Object | Out-String | Write-Debug
                    $PsCommand | ForEach-Object {
                        Write-Verbose "Killing process: Name=$($_.Name), Id=$($_.Id)"
                        Try
                        {
                            $_.Kill()
                        }
                        Catch
                        {
                            Write-Error 'Failed to kill process!'
                        }
                    }
                    break
                }
            }
            Start-Sleep 1
        }
        While(Receive-AsyncStatus -Pipelines $AsyncPipelines | Where-Object {!$_.Completed}) # Loop until all pipelines are finished

        Write-Verbose 'Waiting for all pipelines to finish...'
        $IoStats = Receive-AsyncResults -Pipelines $AsyncPipelines
        Write-Verbose 'All pipelines are finished'

        Write-Verbose 'Collecting StdErr for all processes'
        $PipeStdErr = $StdErrWorkers |
            ForEach-Object {
                $Encoding = $_.Src.StartInfo.StandardOutputEncoding
                if(!$Encoding)
                {
                    $Encoding = [System.Text.Encoding]::Default
                }
                @{
                    FileName = $_.Src.StartInfo.FileName
                    StdErr = $Encoding.GetString($_.Dst.ToArray())
                    ExitCode = $_.Src.ExitCode
                }
            } | 
                Select-Object   @{Name = 'FileName' ; Expression = {$_.FileName}},
                                @{Name = 'StdErr' ; Expression = {$_.StdErr}},
                                @{Name = 'ExitCode' ; Expression = {$_.ExitCode}}

        if($IoWorkers[-1].Dst -is [System.IO.MemoryStream])
        {
            Write-Verbose 'Collecting final pipeline output'
                if($IoWorkers[-1].Src -is [System.Diagnostics.Process])
                {
                    $Encoding = $IoWorkers[-1].Src.StartInfo.StandardOutputEncoding
                }
                if(!$Encoding)
                {
                    $Encoding = [System.Text.Encoding]::Default
                }
                $PipeResult = $Encoding.GetString($IoWorkers[-1].Dst.ToArray())
        }


        Write-Verbose 'Closing and disposing I\O streams'
        . $CleanUp

        $PsCommand |
            ForEach-Object {
                $_.Refresh()
                if(!$_.HasExited)
                {
                    Write-Verbose "Process is still active: Name=$($_.Name), Id=$($_.Id)"
                    if(!$ProcessTimeout)
                    {
                        $ProcessTimeout = -1
                    }
                    else
                    {
                        $WaitForExitProcessTimeout = $ProcessTimeout * 1000
                    }
                    Write-Verbose "Waiting for process to exit (Process Timeout = $ProcessTimeout)"
                    if(!$_.WaitForExit($WaitForExitProcessTimeout))
                    {
                        Try
                        {
                            Write-Verbose 'Trying to kill it'
                            $_.Kill()
                        }
                        Catch
                        {
                            Write-Error "Failed to kill process $_"
                        }
                    }
                }
                Write-Verbose "Disposing process object: Name=$($_.StartInfo.FileName)"
                $_.Dispose()
            }

        Write-Verbose 'Disposing runspace pool'
        # http://stackoverflow.com/questions/21454252/how-to-cleanup-resources-in-a-dll-when-powershell-ise-exits-like-new-pssession
        $RunspacePool.Dispose()

        if($ForceGC)
        {
            Write-Verbose 'Forcing garbage collection'
            Invoke-GarbageCollection
        }
    
        if(!$RawData)
        {
            New-Object -TypeName psobject -Property @{Result = $PipeResult ; Status = $PipeStdErr}
        }
        else
        {
            $PipeResult
        }
    }
}