Create directories and subdirectories in Powershell to move files

i am truly bad at complex regex patterns [blush], so this is done with simple string ops, mostly.

what the code does ...

• fakes reading in some files
  when you have tested this and it works as needed on all your test files, replace the entire #region/#endregion block with a Get-ChildItem call.
• iterates thru the collection
• splits the BaseName on ak & saves it for later use
• checks for a the two short file layouts
• checks for 1 _ versus 2
• builds the $Dir string for each of those 2 filename layouts
• builds the long file name $Dir
• uses the previous $Dir stuff to build the $FullDest for each file
• shows the various stages for each file

that last section would be replaced with your mkdir & Move-Item commands.

the code ...

#region >>> fake reading in files
#    when ready to use the real things, use $Get-ChildItem
$InStuff = @'
MM0245AK625_G03_701.txt
MM0245AK830_G04_701.txt
VY0245AK_G03.txt
VY0245AK_G03_701.txt
VY0245AK625_G03.txt
VY0245AK625_G03_701.txt
VY0345AK625_G03_701.txt
'@ -split [System.Environment]::NewLine |
    ForEach-Object {
        [System.IO.FileInfo]$_
        }
#endregion >>> fake reading in files

foreach ($IS_Item in $InStuff)
    {
    $BNSplit_1 = $IS_Item.BaseName -split 'ak'

    if ($BNSplit_1[-1].StartsWith('_'))
        {
        if (($BNSplit_1[-1] -replace '[^_]').Length -eq 1)
            {
            $Dir = '{0}\{1}' -f $IS_Item.BaseName.Substring(0, 2),
                    $IS_Item.BaseName.Substring(0, 6)
            }
            else
            {
            $Dir = '{0}\{1}\{2}' -f $IS_Item.BaseName.Substring(0, 2),
                $IS_Item.BaseName.Substring(0, 6),
                $IS_Item.BaseName.Split('_')[1]
            }
        }
        else
        {
        $Dir = '{0}\{1}\{2}\{3}' -f $IS_Item.BaseName.Substring(0, 2),
            $IS_Item.BaseName.Substring(0, 6),
            $BNSplit_1[-1].Split('_')[0],
            $BNSplit_1[-1].Split('_')[1]

        }

    $FullDest = Join-Path -Path $Dir -ChildPath $IS_Item

    #region >>> show what was done with each file        
    #    replace this block with your MkDir & Move-Item commands
    $IS_Item.Name
    $Dir
    $FullDest
    'depth = {0}' -f ($FullDest.Split('\').Count - 1)
    '=' * 20
    #endregion >>> show what was done with each file        
    }

the output ...

MM0245AK625_G03_701.txt
MM\MM0245\625\G03
MM\MM0245\625\G03\MM0245AK625_G03_701.txt
depth = 4
====================
MM0245AK830_G04_701.txt
MM\MM0245\830\G04
MM\MM0245\830\G04\MM0245AK830_G04_701.txt
depth = 4
====================
VY0245AK_G03.txt
VY\VY0245
VY\VY0245\VY0245AK_G03.txt
depth = 2
====================
VY0245AK_G03_701.txt
VY\VY0245\G03
VY\VY0245\G03\VY0245AK_G03_701.txt
depth = 3
====================
VY0245AK625_G03.txt
VY\VY0245\625\G03
VY\VY0245\625\G03\VY0245AK625_G03.txt
depth = 4
====================
VY0245AK625_G03_701.txt
VY\VY0245\625\G03
VY\VY0245\625\G03\VY0245AK625_G03_701.txt
depth = 4
====================
VY0345AK625_G03_701.txt
VY\VY0345\625\G03
VY\VY0345\625\G03\VY0345AK625_G03_701.txt
depth = 4
====================

I would first split each file BaseName on the underscore. Then use a regex to split the first part into several array elements, combine that with a possible second part of the split in order to create the destination folder path for the files.

$DataPath = "$PSScriptRoot\Test"
$files = Get-ChildItem -Path $DataPath -Filter '*_*.txt' -File
foreach ($file in $files) {
    $parts = $file.BaseName -split '_'
    # regex your way to split the first part into path elements (remove empty items)
    $folders = [regex]::Match($parts[0], '(?i)^(.{2})(\d{4})[A-Z]{2}(\d{3})?').Groups[1..3].Value | Where-Object { $_ -match '\S'}
    # the second part is a merge with the first part
    $folders[1] = $folders[0] + $folders[1]
    # if there was a third part after the split on the underscore, add $part[1] (i.e. 'Gxx') to the folders array
    if ($parts.Count -gt 2) { $folders += $parts[1] }

    # join the array elements with a backslash (i.e. [System.IO.Path]::DirectorySeparatorChar)
    # and join all tat to the $DataPath to create the full destination for the file
    $target = Join-Path -Path $DataPath -ChildPath ($folders -join '\')

    # create the folder if that does not yet exist
    $null = New-Item -Path $target -ItemType Directory -Force
    # move the file to that (new) directory
    $file | Move-Item -Destination $target -WhatIf
}

^{The -WhatIf switch makes the code not move anything to the new destination, it will only display where the file would go to. Once you are happy with that information, remove -WhatIf and run the code again}

After moving your filestructure will look like this:

D:\TEST
+---MM
|   \---MM0245
|       +---625
|       |   \---G03
|       |           MM0245AK625_G03_701.txt
|       |           
|       \---830
|           \---G04
|                   MM0245AK830_G04_701.txt
|                   
\---VY
    +---VY0245
    |   |   VY0245AK_G03.txt
    |   |   
    |   +---625
    |   |   |   VY0245AK625_G03.txt
    |   |   |   
    |   |   \---G03
    |   |           VY0245AK625_G03_701.txt
    |   |           
    |   \---G03
    |           VY0245AK_G03_701.txt
    |           
    \---VY0345
        \---625
            \---G03
                    VY0345AK625_G03_701.txt