tags:

views:

2691

answers:

4

I need to split a large (500MB) text file (a log4net exception file) into managle chunks like 100 5MB files would be fine.

I would think this should be a walk in the park for PowerShell. Any suggestions?

+10  A: 

This is a somewhat easy task for PowerShell, complicated by the fact that the standard Get-Content cmdlet doesn't handle very large files too well. What I would suggest to do is use the .NET StreamReader class to read the file line by line in your PowerShell script and use the Add-Content cmdlet to write each line to a file with an ever-increasing index in the filename. Something like this:

$count = 1
$fileName = "{0}{1}.{2}" -f ($rootName, $count, $ext)
while(($line = $reader.ReadLine()) -ne null)
{
    Add-Content -path $fileName -value $line
    if((Get-ChildItem -path $fileName).Length -ge $upperBound)
    {
        ++$count
        $fileName = "{0}{1}.{2}" -f ($rootName, $count, $ext)
    }
}

$reader.Close()
Lee
This is exactly what I was looking for, and thanks for confirming my hunch that get-content is not great with large files.
Ralph Shillington
Helpful tip: You can express numbers like this ... $upperBound = 5MB
Lee
+2  A: 

I often need to do the same thing. The trick is getting the header repeated into each of the split chunks. I wrote the following cmdlet (PowerShell v2 CTP 3) and it does the trick.

##############################################################################
#.SYNOPSIS
# Breaks a text file into multiple text files in a destination, where each
# file contains a maximum number of lines.
#
#.DESCRIPTION
# When working with files that have a header, it is often desirable to have
# the header information repeated in all of the split files. Split-File
# supports this functionality with the -rc (RepeatCount) parameter.
#
#.PARAMETER Path
# Specifies the path to an item. Wildcards are permitted.
#
#.PARAMETER LiteralPath
# Specifies the path to an item. Unlike Path, the value of LiteralPath is
# used exactly as it is typed. No characters are interpreted as wildcards.
# If the path includes escape characters, enclose it in single quotation marks.
# Single quotation marks tell Windows PowerShell not to interpret any
# characters as escape sequences.
#
#.PARAMETER Destination
# (Or -d) The location in which to place the chunked output files.
#
#.PARAMETER Count
# (Or -c) The maximum number of lines in each file.
#
#.PARAMETER RepeatCount
# (Or -rc) Specifies the number of "header" lines from the input file that will
# be repeated in each output file. Typically this is 0 or 1 but it can be any
# number of lines.
#
#.EXAMPLE
# Split-File bigfile.csv 3000 -rc 1
#
#.LINK 
# Out-TempFile
##############################################################################
function Split-File {

    [CmdletBinding(DefaultParameterSetName='Path')]
    param(

        [Parameter(ParameterSetName='Path', Position=1, Mandatory=$true, ValueFromPipeline=$true, ValueFromPipelineByPropertyName=$true)]
        [String[]]$Path,

        [Alias("PSPath")]
        [Parameter(ParameterSetName='LiteralPath', Mandatory=$true, ValueFromPipelineByPropertyName=$true)]
        [String[]]$LiteralPath,

        [Alias('c')]
        [Parameter(Position=2,Mandatory=$true)]
        [Int32]$Count,

        [Alias('d')]
        [Parameter(Position=3)]
        [String]$Destination='.',

        [Alias('rc')]
        [Parameter()]
        [Int32]$RepeatCount

    )

    process {

        # yeah! the cmdlet supports wildcards
        if ($LiteralPath) { $ResolveArgs = @{LiteralPath=$LiteralPath} }
        elseif ($Path) { $ResolveArgs = @{Path=$Path} }

        Resolve-Path @ResolveArgs | %{

            $InputName = [IO.Path]::GetFileNameWithoutExtension($_)
            $InputExt  = [IO.Path]::GetExtension($_)

            if ($RepeatCount) { $Header = Get-Content $_ -TotalCount:$RepeatCount }

            # get the input file in manageable chunks

            $Part = 1
            Get-Content $_ -ReadCount:$Count | %{

                # make an output filename with a suffix
                $OutputFile = Join-Path $Destination ('{0}-{1:0000}{2}' -f ($InputName,$Part,$InputExt))

                # In the first iteration the header will be
                # copied to the output file as usual
                # on subsequent iterations we have to do it
                if ($RepeatCount -and $Part -gt 1) {
                    Set-Content $OutputFile $Header
                }

                # write this chunk to the output file
                Write-Host "Writing $OutputFile"
                Add-Content $OutputFile $_

                $Part += 1

            }

        }

    }

}
Josh Einstein
+1  A: 

I've made a little modification to split files based on size of each part.

##############################################################################
#.SYNOPSIS
# Breaks a text file into multiple text files in a destination, where each
# file contains a maximum number of lines.
#
#.DESCRIPTION
# When working with files that have a header, it is often desirable to have
# the header information repeated in all of the split files. Split-File
# supports this functionality with the -rc (RepeatCount) parameter.
#
#.PARAMETER Path
# Specifies the path to an item. Wildcards are permitted.
#
#.PARAMETER LiteralPath
# Specifies the path to an item. Unlike Path, the value of LiteralPath is
# used exactly as it is typed. No characters are interpreted as wildcards.
# If the path includes escape characters, enclose it in single quotation marks.
# Single quotation marks tell Windows PowerShell not to interpret any
# characters as escape sequences.
#
#.PARAMETER Destination
# (Or -d) The location in which to place the chunked output files.
#
#.PARAMETER Size
# (Or -s) The maximum size of each file. Size must be expressed in MB.
#
#.PARAMETER RepeatCount
# (Or -rc) Specifies the number of "header" lines from the input file that will
# be repeated in each output file. Typically this is 0 or 1 but it can be any
# number of lines.
#
#.EXAMPLE
# Split-File bigfile.csv -s 20 -rc 1
#
#.LINK 
# Out-TempFile
##############################################################################
function Split-File {

    [CmdletBinding(DefaultParameterSetName='Path')]
    param(

        [Parameter(ParameterSetName='Path', Position=1, Mandatory=$true, ValueFromPipeline=$true, ValueFromPipelineByPropertyName=$true)]
        [String[]]$Path,

        [Alias("PSPath")]
        [Parameter(ParameterSetName='LiteralPath', Mandatory=$true, ValueFromPipelineByPropertyName=$true)]
        [String[]]$LiteralPath,

        [Alias('s')]
        [Parameter(Position=2,Mandatory=$true)]
        [Int32]$Size,

        [Alias('d')]
        [Parameter(Position=3)]
        [String]$Destination='.',

        [Alias('rc')]
        [Parameter()]
        [Int32]$RepeatCount

    )

    process {

  # yeah! the cmdlet supports wildcards
        if ($LiteralPath) { $ResolveArgs = @{LiteralPath=$LiteralPath} }
        elseif ($Path) { $ResolveArgs = @{Path=$Path} }

        Resolve-Path @ResolveArgs | %{

            $InputName = [IO.Path]::GetFileNameWithoutExtension($_)
            $InputExt  = [IO.Path]::GetExtension($_)

            if ($RepeatCount) { $Header = Get-Content $_ -TotalCount:$RepeatCount }

   Resolve-Path @ResolveArgs | %{

    $InputName = [IO.Path]::GetFileNameWithoutExtension($_)
    $InputExt  = [IO.Path]::GetExtension($_)

    if ($RepeatCount) { $Header = Get-Content $_ -TotalCount:$RepeatCount }

    # get the input file in manageable chunks

    $Part = 1
    $buffer = ""
    Get-Content $_ -ReadCount:1 | %{

     # make an output filename with a suffix
     $OutputFile = Join-Path $Destination ('{0}-{1:0000}{2}' -f ($InputName,$Part,$InputExt))

     # In the first iteration the header will be
     # copied to the output file as usual
     # on subsequent iterations we have to do it
     if ($RepeatCount -and $Part -gt 1) {
      Set-Content $OutputFile $Header
     }

     # test buffer size and dump data only if buffer is greater than size
     if ($buffer.length -gt ($Size * 1MB)) {
      # write this chunk to the output file
      Write-Host "Writing $OutputFile"
      Add-Content $OutputFile $buffer
      $Part += 1
      $buffer = ""
     } else {
      $buffer += $_ + "`r"
     }
    }
   }
        }
    }
}
+2  A: 

I found this question while trying to split multiple contacts in a single vCard VCF file to separate files. Here's what I did based on Lee's code. I had to look up how to create a new StreamReader object and changed null to $null.

$reader = new-object System.IO.StreamReader("C:\Contacts.vcf")
$count = 1
$filename = "C:\Contacts\{0}.vcf" -f ($count) 

while(($line = $reader.ReadLine()) -ne $null)
{
    Add-Content -path $fileName -value $line

    if($line -eq "END:VCARD")
    {
        ++$count
        $filename = "C:\Contacts\{0}.vcf" -f ($count)
    }
}

$reader.Close()