Create Directory Using Partial Path - powershell

Question

Problem
In PowerShell, is it possible to create a new file directory using a partial path that has wildcards (Ex: C:\*\SomeFolder\MyBackup)? If so, how?
Details
I am working with PowerShell to create an application, and one part of that application has the user designate a backup directory. This directory could be an exact path, but I am also expecting that wildcards could be used. With that said, I know I can easily use MD C:\SomePath\ or New-Item "C:\SomePath\" -FileType Directory IF the path provided is absolute; however, it fails whenever I try to do this with wild cards.
Examples: These all fail when I attempt them
MD "C:\*\MyBackups\AppBackup"
New-Item "C:\*\MyApp\Backup" -FileType Directory
$fullPath = "C:\*\MyApp\Backup" | Resolve-Path
$fullPath = Resolve-Path "C:\*\MyApp\Backup"
$ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath("C:\*\MyApp\Backup")
Now, I understand part of the failure is the wildcard itself as the command doesn't understand how to interpret it.
I have researched things like New-Item, Convert-Path, Resolve-Path, and Split-Path, but haven't been able to find anything that is related to what I'm trying to do.

Answer 1

md, which is an alias for a wrapper function around New-Item, expects an exact path. If you want to create a directory based on a wildcard path you need something like this:
Get-ChildItem 'C:\*\MyBackups' | ForEach-Object {
New-Item -Type Directory -Path $_.FullName -Name 'MyBackup' | Out-Null
}
Note that wildcards in a path usually cover just one level of hierarchy. If you want to find any subfolder MyBackups on the C: drive you need an approach like this:
Get-ChildItem 'C:\' -Filter 'MyBackups' -Directory -Recurse | ForEach-Object {
New-Item -Type Directory -Path $_.FullName -Name 'MyBackup' | Out-Null
}

Answer 2

If you'r attempting to take user input and make that represent the *, then you need to represent that in your code. The only area that confuses me is that you have wildcards. I don't think I fully understand what purpose the wildcards serve in your script.
$backupTemplate = 'MyBackups\AppBackup'
#This can be a lot of different methods of input, from a Read-Host or what I have below
$dirSelector = New-Object System.Windows.Forms.FolderBrowserDialog -Property #{ SelectedPath = Get-Location }
$dirSelector.ShowDialog() | Out-Null
$dirSelector.SelectedPath
$bckupDir = "$($dirSelector.SelectedPath)\$backupTemplate"
#EDIT: You were indicating below you needed to find the parent directory for the 'anchor'. Added this here for that.
$parentDir = (Get-Item $dirSelector.SelectedPath).Parent.FullName
if(-not (Test-Path -Path $bckupDir))
{
New-Item -Path $bckupDir
}
#Execute your code here on whatever is doing the backup.
EDIT/Addition:
If the problem you are running in to is that the User sets their backup directory once and then may not remember where it was, then you should look into storing this variable somewhere that both the user can recall in your cmdlets and your cmdlets can access to utilize.
A very common way to do this is to create a file that holds the settings that the user makes in regards to whatever you are attempting to accomplish.
A nice way to do this is to create a standard object and then export that as an CliXML (or JSON or whatever format you like to work with) like so:
$userSettings = New-Object -TypeName psobject
$userSettings | Add-Member -MemberType NoteProperty -Name User -Value $env:USERNAME
$userSettings | Add-Member -MemberType NoteProperty -Name LastUpdate -Value $(Get-Date -format u)
$userSettings | Add-Member -MemberType NoteProperty -Name BackupDirectory -Value $dirSelector.SelectedPath
$userSettings | Export-Clixml -Path "$env:USERPROFILE\psUserProf.xml"
#when you need to get the users backup folder in the future you just import the profile and work from there
$userSettings = Import-Clixml -Path "$env:USERPROFILE\psUserProf.xml"
$userSettings.BackupDirectory
Note though that if your users have more than one computer you'll need to facilitate a way for these settings to follow them.