Split Large Binary Files in PowerShell

# Example usage:
#
#   Import-Module .\Split-File.ps1
#
#   Split-File -InputFile "path/to/big-file.zip" -OutputDirectory "path/to/split/output/files" -Verbose
#   Unsplit-File -InputDirectory "path/to/split/output/files" -OutputDirectory "path/to" -OutputFile big-file.zip

function Split-File
{
    <#-- Another stackoverflow production
    https://stackoverflow.com/questions/4533570/in-powershell-how-do-i-split-a-large-binary-file
    --#>

    [CmdletBinding()]
    Param (
        [Parameter(Mandatory = $true, ValueFromPipeLine = $true, ValueFromPipelineByPropertyName = $true)]
        [String]
        $InputFile,

        [Parameter(Mandatory = $true)]
        [String]
        $OutputDirectory,

        [Parameter(Mandatory = $false)]
        [String]
        $OutputFilePrefix = "chunk",

        [Parameter(Mandatory = $false)]
        [Int32]
        $ChunkSize = 4096
    )

    Begin
    {
        Write-Output "Beginning file split..."
    }

    Process
    {
        if (-not (Test-Path -Path $OutputDirectory))
        {
            New-Item -ItemType Directory $OutputDirectory | Out-Null
            Write-Verbose "Created OutputDirectory: $OutputDirectory"
        }

        $FileStream = [System.IO.File]::OpenRead($InputFile)
        $ByteChunks = New-Object byte[] $ChunkSize
        $ChunkNumber = 1

        While ($BytesRead = $FileStream.Read($ByteChunks, 0, $ChunkSize))
        {
            $OutputFile = Join-Path -Path $OutputDirectory -ChildPath "$OutputFilePrefix$ChunkNumber"
            $OutputStream = [System.IO.File]::OpenWrite($OutputFile)
            $OutputStream.Write($ByteChunks, 0, $BytesRead)

            $OutputStream.Close()

            Write-Verbose "Wrote File: $OutputFile"

            $ChunkNumber += 1
        }
    }

    End
    {
        Write-Output "Finished splitting file."
    }
}

function Unsplit-File
{
    [CmdletBinding()]
    Param (
        [Parameter(Mandatory = $true)]
        [String]
        $InputDirectory,

        [Parameter(Mandatory = $false)]
        [String]
        $InputFilePrefix = "chunk",

        [Parameter(Mandatory = $true)]
        [String]
        $OutputDirectory,

        [Parameter(Mandatory = $true)]
        [String]
        $OutputFile
    )

    Begin
    {
        Write-Output "Beginning file unsplit..."
    }

    Process
    {
        if (-not (Test-Path -Path $OutputDirectory))
        {
            New-Item -ItemType Directory $OutputDirectory | Out-Null
            Write-Verbose "Created OutputDirectory: $OutputDirectory"
        }

        $OutputPath = Join-Path -Path $OutputDirectory -ChildPath $OutputFile
        $OutputStream = [System.Io.File]::OpenWrite($OutputPath)

        $ChunkNumber = 1
        $InputFilename = Join-Path -Path $InputDirectory -ChildPath "$InputFilePrefix$ChunkNumber"

        while (Test-Path $InputFilename)
        {
            $FileBytes = [System.IO.File]::ReadAllBytes($InputFilename)
            $OutputStream.Write($FileBytes, 0, $FileBytes.Count)

            Write-Verbose "Unsplit File: $InputFilename"

            $ChunkNumber += 1
            $InputFilename = Join-Path -Path $InputDirectory -ChildPath "$InputFilePrefix$ChunkNumber"
        }

        $OutputStream.close()
    }

    End
    {
        Write-Output "Finished unsplitting file."
    }
}