Split large CSV files into smaller files while preserving the headers

split-csv.ps1

# Splitting large CSV files into smaller ones, preserving the headers
# By Joannes Vermorel, 2015-12-18
function Split-Csv 
{
    param
    (
        [string] $file,
        [int] $maxLines
    )

    $isFirst = $true;
    $lineCount = 0;

    if($file.StartsWith(".\"))
    {
        $file = (Get-Item -Path $file -Verbose).FullName;
    }

    $path = [System.IO.Path]::GetDirectoryName($file);
    $output = [System.IO.Path]::GetFileNameWithoutExtension($file);
    $outext = [System.IO.Path]::GetExtension($file);

    $outputCount = 0;

    $stream = [System.IO.StreamWriter] ($path + "\\" + $output + "-" + $outputCount + $outext);

    foreach ($line in [System.IO.File]::ReadLines($file))
    {
        if($isFirst) 
        {
            $header = $line;
            $stream.WriteLine($header);
            $lineCount = 1;
            $isFirst = $false;
        }
        else
        {
            if($lineCount -eq 0)
            {
                $stream = [System.IO.StreamWriter] ($path + "\\" + $output + "-" + $outputCount + $outext);
                $stream.WriteLine($header);
                $stream.WriteLine($line);
                $lineCount = 1;
            }
            else
            {
                $stream.WriteLine($line);
                $lineCount = $lineCount + 1;
            
                if($lineCount -gt $maxLines)
                {
                    $stream.Flush();
                    $stream.Close();
                    $lineCount = 0;
                    $outputCount = $outputCount + 1;
                }
            }
        }
    }

    $stream.Flush();
    $stream.Close();
}