Prof. Powershell

PowerShell File Frontier, Part 7: Zipped Files from Scratch

• By Jeffery Hicks
• 10/06/2014

The finale of Prof. PowerShell's 7-part series ends with creating a zipped file.

More on this topic:

• The File Frontier, Part 1
• The PowerShell File Frontier, Part 2: File Length
• PowerShell File Frontier, Part 3: Right Tool for the Job
• PowerShell File Frontier, Part 4: Zipped Files
• PowerShell File Frontier, Part 5: Analyzing Compressed Flies
• File Frontier, Part 6: Adding Files to a Zip Archive

I hope you've not only been seeing how to create zip files from PowerShell but also how to discover properties and methods for .NET classes. As you should have picked up from the last article, it is also very important to at least try to read through any documentation you can find. We have been working with existing zip archives. Today, let's create one from scratch The [System.IO.Compression.ZipFile] class has a method called CreateFromDirectory().

PS C:\> [System.IO.Compression.ZipFile].getmethods().Name  | get-unique

  OpenRead

  Open

  CreateFromDirectory

  ExtractToDirectory

  ToString

  Equals

  GetHashCode

  GetType

Using the techniques I've taught you , here's how to use it.

PS C:\>  [System.IO.Compression.ZipFile]::CreateFromDirectory.OverloadDefinitions

  static void CreateFromDirectory(string  sourceDirectoryName, string destinationArchiveFileName)

  static void CreateFromDirectory(string  sourceDirectoryName, string destinationArchiveFileName, System.IO.Compression.

  CompressionLevel compressionLevel, bool  includeBaseDirectory)

  static void CreateFromDirectory(string  sourceDirectoryName, string destinationArchiveFileName, System.IO.Compression.

  CompressionLevel compressionLevel, bool  includeBaseDirectory, System.Text.Encoding entryNameEncoding)

I'm willing to test it out:

PS C:\>  [System.IO.Compression.ZipFile]::CreateFromDirectory("c:\work",

  "c:\zip\mywork.zip","optimal",$True)

That last value, $True, will include C:\work which is what I want. Notice that when we've been invoking methods, there is no support for –WhatIf or –Confirm. That's one of the disadvantages of using a .NET class instead of a cmdlet.

Next, let's turn around and open the file in PowerShell.

PS C:\> $zip =  [System.IO.Compression.ZipFile]::OpenRead("c:\zip\mywork.zip")

  PS C:\> $zip.entries.count

  118

  PS C:\> $zip.entries[0]
Archive          : System.IO.Compression.ZipArchive

  CompressedLength : 166

  FullName         : work\admins.csv

  LastWriteTime    : 3/5/2014 2:14:42 PM -05:00

  Length           : 449

  Name              : admins.csv

Did you notice that the fullname includes the Work path? That's because I included it when I built the archive. It isn't too much more work to quickly report on the contents.

PS C:\> [pscustomobject]@{

  Count=$zip.entries.count

  TotalSize=($zip.entries | measure length  -sum).sum

  TotalCompressed=($zip.entries | measure  compressedlength -sum).sum

  }
   Count                               TotalSize                         TotalCompressed

  -----                               ---------                         ---------------

  118                                28037292                                 8111399

But let's say you want to archive all of your PowerShell scripts last modified in August 2014. First, I need to have an expression to find all the files.

dir c:\scripts\*.ps1 -recurse | where {$_.LastWriteTime  -ge "8/1/2014" -and $_.LastWriteTime -lt "9/1/2014"}

From looking at the ZipFile methods, the Open() method has a parameter that will allow me to create an empty zip file.

$zip = [System.IO.Compression.ZipFile]::Open("c:\zip\August2014.zip","Create")

When the file is open, all I need to do is add an entry for each file. This is a great example for using ForEach-Object.

dir c:\scripts\*.ps1 -recurse | 
  where {$_.LastWriteTime -ge  "8/1/2014" -and $_.LastWriteTime -lt "9/1/2014"} |

  foreach -begin {

  $zip =  [System.IO.Compression.ZipFile]::Open("c:\zip\August2014.zip","Create")

  } -process {

  #split  off the parent path for the entry name

  $entry= $_.FullName.Split(":")[1].substring(1)

  [System.IO.Compression.ZipFileExtensions]::CreateEntryFromFile($zip,$_.fullname,

  $entry,"optimal")

  } -end { 

  $zip.Dispose()

  }

I create a new zip in the Begin scriptblock, add an entry for each file in the Process scriptblock using the directory path for the entry and when finished, close the file.

And there you have it. With a little work you can create some simple archiving scripts using the file system and the compression classes. As you may have seen, there are methods for extracting and removing files from zip archives, but I'll leave those for you to figure out how to use. Hopefully, you've picked up enough techniques over the last few articles.