Add folder date to the foldername - powershell

Question

I have a script which recursively modifies the "creation date" and the"modified date" of folders to match the oldest and newest files in folders (image files).
After that I want to add the creation date of each folder as a prefix to its name. I have written the code that creates the desired name but I don't know how to rename the folders.
$colFolder = Get-ChildItem -Recurse "." |
Where-Object {$_.mode -match "d"} |
Sort-Object Fullname -Descending
$VerbosePreference = "Continue"
foreach ($strFolder In $colFolder) {
Trap [Exception] {
Write-Verbose "TRAPPED:"
Write-Verbose $_.Exception.Message;
Write-Verbose $strFolder.FullName
Continue
}
$Path = $strFolder.FullName
$Folder = Get-Item $Path
# Get Newest file in folder
$strOldestTime = (Get-ChildItem $Path | Sort-Object LastWriteTime | Select-Object -First 1).LastWriteTime
$strNewestTime = (Get-ChildItem $Path | Sort-Object LastWriteTime | Select-Object -Last 1).LastWriteTime
# Change the date to match the newest file if it doesn't already
$Folder.CreationTime = $strOldestTime
$Folder.LastWriteTime = $strNewestTime
# add the date as the prefix of the folder (in which the files are)
$date = $strOldestTime.ToString('yyyy-MM-dd')
$foldername = $Folder.Name.split("\")[-1]
Write-Verbose "$date- $foldername"
#now rename the folder to above name
}

Answer 1

Renaming folders can be done as #onupdatecascade described in his answer.
Rename-Item -Path $Folder.FullName -NewName $newname
If you have at least PowerShell v3 (which I highly recommend) you can use the parameter -LiteralPath for the current folder path to avoid issues with special characters:
Rename-Item -LiteralPath $Folder.FullName -NewName $newname
With that said, there are a couple improvements to your code I'd like to suggest.
Get-ChildItem -Recurse ".":
Get-ChildItem uses the current working directory by default, so "." can be omitted.
Where-Object {$_.mode -match "d"}:
The objects you get from Get-ChildItem have a boolean property IsContainer that indicates whether you have a folder or not. No need to use a regex match on the mode. Also, in PowerShell v3 and newer you can omit this step entirely, because the Get-ChildItem cmdlet has an additional parameter -Directory that lists only folders.
Misused hungarian notation (pt.1):
foreach ($strFolder In $colFolder) {
The loop variable $strFolder does not contain strings, but DirectoryInfo objects. This is a prime example for why I consider hungarian notation a pointless waste of space.
Avoid unnecessary steps.
$Path = $strFolder.FullName
$Folder = Get-Item $Path
$strFolder already contains a DirectoryInfo object. The above two statements just convert it to a path string and back to a DirectoryInfo object. Simply make $Folder your loop variable (see above).
Avoid duplicate code (particularly duplicate disk operations):
$strOldestTime = (Get-ChildItem $Path | Sort-Object LastWriteTime | Select-Object -First 1).LastWriteTime
$strNewestTime = (Get-ChildItem $Path | Sort-Object LastWriteTime | Select-Object -Last 1).LastWriteTime
Instead of listing and sorting the child items multiple times run the statement just once and collect the result in a variable:
$items = Get-ChildItem $Path | Sort-Object LastWriteTime
$strOldestTime = ($items | Select-Object -First 1).LastWriteTime
$strNewestTime = ($items | Select-Object -Last 1).LastWriteTime
Also, I would simply expand the LastWriteTime property instead of running Select-Object in a subexpression:
$strOldestTime = $items | Select-Object -First 1 -Expand LastWriteTime
$strNewestTime = $items | Select-Object -Last 1 -Expand LastWriteTime
Misused hungarian notation (pt.2):
$strOldestTime and $strNewestTime contain DateTime objects, not strings.
$foldername = $Folder.Name.split("\")[-1]:
The Name property already contains the folder name without path, so there's nothing to split off.
Construct the new folder name from the date and the current name by using the format operator:
$newname = '{0:yyyy-MM-dd} - {1}' -f $oldestTime, $Folder.Name
If there's a possibility that you'll run the script multiple times you may want to remove an existing leading date from the folder name so that the dates won't "stack":
$Folder.Name -replace '^\d{4}-\d{2}-\d{2} - '
Simplified code:
$colFolder = Get-ChildItem -Recurse |
Where-Object { $_.PSIsContainer } |
Sort-Object Fullname -Descending
foreach ($folder in $colFolder) {
$items = Get-ChildItem $folder.FullName | Sort-Object LastWriteTime
$folder.CreationTime = $items | Select-Object -First 1 -Expand LastWriteTime
$folder.LastWriteTime = $items | Select-Object -Last 1 -Expand LastWriteTime
$newname = '{0:yyyy-MM-dd} - {1}' -f $folder.CreationTime, ($folder.Name -replace '^\d{4}-\d{2}-\d{2} - ')
Rename-Item -Path $folder.FullName -NewName $newname
}
or (PowerShell v3 and newer):
$colFolder = Get-ChildItem -Recurse -Directory |
Sort-Object Fullname -Descending
foreach ($folder in $colFolder) {
$items = Get-ChildItem $folder.FullName | Sort-Object LastWriteTime
$folder.CreationTime = $items | Select-Object -First 1 -Expand LastWriteTime
$folder.LastWriteTime = $items | Select-Object -Last 1 -Expand LastWriteTime
$newname = '{0:yyyy-MM-dd} - {1}' -f $folder.CreationTime, ($folder.Name -replace '^\d{4}-\d{2}-\d{2} - ')
Rename-Item -LiteralPath $folder.FullName -NewName $newname
}

Answer 2

Have you tried
Rename-Item oldname newname
It works for simple examples, but could break with folders nested in other folders, and recursion, because you might rename a folder before the script is done with it.
To manage that you can do them in order by length (paths to children being by definition longer than the paths of the parents). Good example here: How do I recursively rename folders with Powershell?