PowerShell create a duplicate folder with zero-size files - powershell

Question

I want to create a 0-filesize mirror image of a set of folder, but while robocopy is really good, it doesn't save all of the information that I would like:
robocopy D:\documents E:\backups\documents_$(Get-Date -format "yyyyMMdd_HHmm")\ /mir /create
The /create switch makes each file in the duplicate folder have zero-size, and that is good, but I would like each file in the duplicate folder to have [size] appended to the end of the name with the size in KB or MB or GB, and the create / last modified time on every file to exactly match the original file. This way, I will have a zero-size duplicate of the folder that I can archive, but which contains all of the relevant information for the files in that directory, showing the size of each and the exact create / last modified times.
Are there good / simple ways to iterate through a tree in PowerShell, and for each item create a zero size file with all relevant information like this?

Answer 1

This would be one way to implement the copy command using the approach I mentioned in the comments. This should give you something to pull ideas from. I didn't intend to spend as much time on it as I did, but I ran it on several directories and found some problems and debugged each problem I encountered. This is a pretty solid example at this point.
function Copy-FolderZeroSizeFiles {
[CmdletBinding()]
param( [Parameter(Mandatory)] [string] $FolderPath,
[Parameter(Mandatory)] [string] $DestinationPath )
$dest = New-Item $DestinationPath -Type Directory -Force
Push-Location -LiteralPath $FolderPath
try {
foreach ($item in Get-ChildItem '.' -Recurse) {
$relPath = Resolve-Path -LiteralPath $item -Relative
$type = if ($item.Attributes -match 'Directory')
{ 'Directory' }
else { 'File' }
$destItem = New-Item "$dest\$relPath" -Type $type -Force
$destItem.Attributes = $item.Attributes
$destItem.LastWriteTime = $item.LastWriteTime
}
} finally {
Pop-Location
}
}
Note: the above implementation is simplistic and represents anything that isn't a directory as a file. That means symbolic links, et al. will be files with no information what they would be linked to.
Here's a function to get the conversion from number of bytes to N.N B/K/M/G format. To get more decimal places, just add 0's to the end of the format strings.
function ConvertTo-FriendlySize($NumBytes) {
switch ($NumBytes) {
{$_ -lt 1024} { "{0,7:0.0}B" -f ($NumBytes) ; break }
{$_ -lt 1048576} { "{0,7:0.0}K" -f ($NumBytes / 1024) ; break }
{$_ -lt 1073741824} { "{0,7:0.0}M" -f ($NumBytes / 1048576) ; break }
default { "{0,7:0.0}G" -f ($NumBytes / 1073741824); break }
}
}
Often, people get these conversions wrong. For instance, it's a common error to use 1024 * 1000 to get Megabytes (which is mixing the base10 value for 1K with the base2 value for 1K) and follow that same logic to get GB and TB.

Answer 2

Here is what I came up with with the additional parts in the question, change $src / $dst as required (D:\VMs is where I keep a lot of Virtual Machines). I have included setting all of CreationTime, LastWriteTime, LastAccessTime so that the backup location with zero-size files is a perfect representation of the source. As I want to use this for archival purposes, I have finally zipped things up and included a date-time stamp in the zipfile name.
# Copy-FolderZeroSizeFiles
$src = "D:\VMs"
$dst = "D:\VMs-Backup"
function ConvertTo-FriendlySize($NumBytes) {
switch ($NumBytes) {
{$_ -lt 1024} { "{0:0.0}B" -f ($NumBytes) ; break } # Change {0: to {0,7: to align to 7 characters
{$_ -lt 1048576} { "{0:0.0}K" -f ($NumBytes / 1024) ; break }
{$_ -lt 1073741824} { "{0:0.0}M" -f ($NumBytes / 1048576) ; break }
default { "{0:0.0}G" -f ($NumBytes / 1073741824); break }
}
}
function Copy-FolderZeroSizeFiles($FolderPath, $DestinationPath) {
Push-Location $FolderPath
if (!(Test-Path $DestinationPath)) { New-Item $DestinationPath -Type Directory }
foreach ($item in Get-ChildItem $FolderPath -Recurse -Force) {
$relPath = Resolve-Path $item.FullName -Relative
if ($item.Attributes -match 'Directory') {
$new = New-Item "$DestinationPath\$relPath" -ItemType Directory -Force -EA Silent
}
else {
$fileBaseName = [System.IO.Path]::GetFileNameWithoutExtension($item.Name)
$fileExt = [System.IO.Path]::GetExtension($item.Name)
$fileSize = ConvertTo-FriendlySize($item.Length)
$new = New-Item "$DestinationPath\$(Split-Path $relPath)\$fileBaseName ($fileSize)$fileExt" -ItemType File
}
"$($new.Name) : creation $($item.CreationTime), lastwrite $($item.CreationTime), lastaccess $($item.LastAccessTime)"
$new.CreationTime = $item.CreationTime
$new.LastWriteTime = $item.LastWriteTime
$new.LastAccessTime = $item.LastAccessTime
$new.Attributes = $item.Attributes # Must this after setting creation/write/access times or get error on Read-Only files
}
Pop-Location
}
Copy-FolderZeroSizeFiles $src $dst
$dateTime = Get-Date -Format "yyyyMMdd_HHmm"
$zipName = "$([System.IO.Path]::GetPathRoot($dst))\$([System.IO.Path]::GetFileName($dst))_$dateTime.zip"
Add-Type -AssemblyName System.IO.Compression.FileSystem
[IO.Compression.ZipFile]::CreateFromDirectory($dst, $zipName)