So I am trying to rename several level1-subfolders from something like "xy_1234" to "1234_xy". So far I've achieved to split the strings into variables, build the new directory-name and rename the directory, but I'm completely failing, when trying to automate the process within a for-loop. Please help.
Get-Item $Path | ForEach ( $a, $b = $Path.split('_') | Rename-Item -NewName { $b + ('_') + $a})
Get-Item $Path | Rename-Item -NewName {
$tokens = $_.Name -split '_' # split the name into tokens
'{0}_{1}' -f $tokens[1], $tokens[0] # output with tokens swapped
} -WhatIf
-WhatIf previews the operation.
As you can see, you can do the parsing as part of the script block passed to Rename-Item's -NewName parameter.
Since -NewName only expects the item's file or directory new name (as opposed to the full path), $_.Name is parsed and a transformation of it is (implicitly) output.
Here's a more succinct formulation, inspired by a tip from LotPings:
Get-Item $Path | Rename-Item -NewName { -join ($_.Name -split '(_)')[-1, 1, 0] }
This relies on PowerShell's ability to slice an array by specifying an array (list) of indices: -1, 1, 0 effectively reverses the elements of the array that $_.Name -split '(_)' returns - note the (...) around _, which ensures that instances of _ are included in the array of tokens returned; the unary form of the -join operator then concatenates the reversed array's elements.
Note: I'm assuming that $Path contains a wildcard expression that matches only the directories of interest.
If you need to be explicit about matching directories only, use Get-ChildItem with the
-Directory switch:
Get-ChildItem $Path -Directory
With a wildcard pattern specifically matching the sample name from your question:
Get-ChildItem [a-z][a-z]_[0-9][0-9][0-9][0-9] -Directory
I think several subfolders should be caught with a GCI
taking the "xy_1234" to "1234_xy" literal:
Get-ChildItem $Path -Dir | Where-Object Name -match '^([a-z]+)_(\d+)$' |
Rename-Item -NewName {$_.Name.Split('_')[1,0] -join ('_')} -WhatIf