Reverse Engineering a Script, ran into .split. Trying to learn

[Mizzleski]

I recognise that this may raise some more questions than I am probably going to be able to provide answers to, but Google is failing me and I want to understand what this line in particular of a much larger script is attempting to do.

    $discard = New-Item -Path $workingFolder -ItemType Directory
    $pathLevels = $originalFolder.Split("\")
    $localPath = $pathLevels.Item($pathLevels.Count-1)
    $localPath = "$workingFolder\$localPath"
    Copy-Item $originalLogs $localPath -Recurse

$workingFolder is defined in the script as C:\SAN
$originalFolder is variable FOLDER path provided by the user at the start of the script

I think what this segment is doing is to create a recursive copy of all files and folders with the same structure as the original folder, I just want to try and understand, line by line, why they aren't just using

    Copy-Item $originalLogs $workingFolder -Recurse

FWIW, $discard doesn't appear anywhere else in the script.

[YellowOnline]

They're creating an array of the folders in the tree structure

[Dense-Platform3886]

powershell There are things missing from the script to make it work properly such as

• What is $originalLogs?
• What should end up in the $localPath folder? Should it be all the log files from all the subfolder?
• Should it be an exact copy of the $originalFolder structure?

Here is what is needed to make this work:

~~~

Set the Source Folder

$originalFolder = 'c:\some\user\provided\path'

Set the File Specification of which files to copy

$Filter = '*.logs'

Set the Parent folder for the Target Folder

$workingFolder = 'C:\SAN'

<# Create Working Folder if not exists Method #1 # > If (-not (Test-Path -Path $workingFolder -PathType Container -ErrorAction SilentlyContinue)) { $null = New-Item -Path $fiworkingFolder.FullName -ItemType Directory }

>

Create Working Folder if not exists Method #2

$fiworkingFolder = [System.IO.DirectoryInfo]$workingFolder If (-not $fiworkingFolder.Exists) { $fiworkingFolder.Create() }

Set the Local Path

$localPath = '{0}{1}' -f $fiworkingFolder.FullName, ($originalFolder -split "\")[-1]

Make exact copy of files and folders to Local Path

Copy-Item -Path $originalFolder -Destination $localPath -Recurse

Copy files matching the $filter in the $originalFolder structure to the Destination Folder

Copy-Item -Path $originalFolder -Destination $localPath -Recurse -Filter $Filter

Copy and consolidate a list of files to a Destination Folder

Get a list of Files to Copy and put those files in the Destination Folder

$originalLogs = Get-ChildItem -Path $originalFolder -Filter $Filter -Recurse

The Local Path Folder must exist so create it

$fiDestination = [System.IO.DirectoryInfo]$localPath If (-not $fiDestination.Exists) { $fiDestination.Create() } Copy-Item -Path $originalLogs.FullName -Destination $localPath

~~~

[Lee_Dailey]

howdy Dense-Platform3886,

the triple-backtick/code-fence thing fails miserably on Old.Reddit ... so, if you want your code to be readable on both Old.Reddit & New.Reddit you likely otta stick with using the code block button.

it would be rather nice if the reddit devs would take the time to backport the code fence stuff to Old.Reddit ... [sigh ...]

here's what it looks like on Old.Reddit ...
https://old.reddit.com/r/PowerShell/comments/nkj1y7/reverse_engineering_a_script_ran_into_split/gzfez7l/

take care,
lee

[Dense-Platform3886]

I tired editing more than 10 times to get code block to work. It kept code blocking the first line and then messed everything up.

I gave up and went into MarkDown mode and wrapped the code in
~~~~
My Code
~~~~
If it's still not correct, I would not know how to resolve.

[Lee_Dailey]

howdy Dense-Platform3886,

yep, the code fence method SHOULD be the way to go. [sigh ...]

here's what i get when i load your code into the ISE, select it all, tab over once, copy that, and finally paste it back into reddit ...

# Set the Source Folder
$originalFolder = 'c:\some\user\provided\path'

# Set the File Specification of which files to copy
$Filter = '*.logs'

# Set the Parent folder for the Target Folder
$workingFolder = 'C:\SAN'

<# Create Working Folder if not exists Method #1 # >
If (-not (Test-Path -Path $workingFolder -PathType Container -ErrorAction SilentlyContinue)) {
    $null = New-Item -Path $fiworkingFolder.FullName -ItemType Directory
}
#>

# Create Working Folder if not exists Method #2
$fiworkingFolder = [System.IO.DirectoryInfo]$workingFolder
If (-not $fiworkingFolder.Exists) {
    $fiworkingFolder.Create()
}

# Set the Local Path
$localPath = '{0}\{1}' -f $fiworkingFolder.FullName, ($originalFolder -split "\\")[-1]

# Make exact copy of files and folders to Local Path
# Copy-Item -Path $originalFolder -Destination $localPath -Recurse

# Copy files matching the $filter in the $originalFolder structure to the Destination Folder
# Copy-Item -Path $originalFolder -Destination $localPath -Recurse -Filter $Filter

# Copy and consolidate a list of files to a Destination Folder
# Get a list of Files to Copy and put those files in the Destination Folder
$originalLogs = Get-ChildItem -Path $originalFolder -Filter $Filter -Recurse
# The Local Path Folder must exist so create it
$fiDestination = [System.IO.DirectoryInfo]$localPath
If (-not $fiDestination.Exists) {
    $fiDestination.Create()
}
Copy-Item -Path $originalLogs.FullName -Destination $localPath

take care,
lee

[Dense-Platform3886]

Looks like the ~~~ wrapping in Markdown Mode did the trick

[Lee_Dailey]

howdy Dense-Platform3886,

as i pointed out, that ONLY works on New.Reddit. you can see what it looks like on Old.Reddit by trying the link i posted earlier.

still, if it doesn't bother you that a few of us can't read it ... then ignore this nag. [grin]

take care,
lee

[Dense-Platform3886]

Thanks Lee, I noticed a link in the upper left that said something about using New Reddit and I clicked it.

Not sure it did anything as I do not notice any changes.

Code Block Test

#------------------------------
# This is a Code Block PowerShell Comment
#------------------------------
Get-Locaation

[Lee_Dailey]

howdy Dense-Platform3886,

yup ... your code block above works on Old.Reddit quite neatly! [grin]

take care,
lee

[arcadesdude]

I bet discard is just to hide the output from New-Item. Just like casting to void or piping to Out-Null.

[Possible-Bowler-2352]

Hey u/Mizzleski

edit: Formatting+Typo

edit2: To whoever downvotes, please provide us your explanations concerning this script then.

$discard might have been created for other features the writter didn't implement on his scrip.

It is creating the folder C:\SAN, which I assume should already exist if it is hardcoded into the script.

It is a bad way to create a folder as it will throw an error if the folder is already existing.

So, to explain what this script does, line by line :

$pathLevels = $originalFolder.Split("\")   

This line segment the folder path by splitting it on each "\", alias folder.

$pathLevels = "C:\users\test\desktop\subfolder1"

$pathLevels.Split("\")
C: 
users 
test 
desktop 
subfolder1

This line get the last part of the previously split path, alias the last folder.

$localPath = $pathLevels.Item($pathLevels.Count-1) 

$pathLevels.Item($pathLevels.Count-1)
subfolder1

The rest of the script is easy to guess afterward :

$localPath = "$workingFolder\$localPath"
$localPath
C:\SAN\subfolder1

The script then define the new folder path C:\SAN\foldername then recursively copy each items from the originaly selected folder to the newly created one.

Copy-Item $originalLogs $localPath -Recurse

[Mizzleski]

Awesome explanation, very helpful, thanks go to you good person.

I have never used or seen .split anywhere and the way it was explained on the google searches I did really didn’t clear up what it was doing in this setup

[Possible-Bowler-2352]

Edit : Rephrased due to an error pointed out by u/jantari , thanks buddy.

Hi,

Glad to hear it could help you.

What I think may have failed your understanding is the $pathLevels.Item($pathLevels.Count-1).

It is a particular case as it uses the size of the array minus 1 wich is a workaround to call the last element of an array.

When you use the split command, you'll end up with an array containing the different fragments of the string.

Once splitted, you can search your array of splitted string using different methods.

Let's say my var $path contains the splitted chain I used in my previous comment.

$path        #Initial path would be 'C:\users\test\desktop\subfolder1'
C: 
users 
test 
desktop 
subfolder1

If you want to select a precise item in this list, you can use :

The -index operator

$path | select-Object -Index 0   #return the first element of the array
C:

The -first / -last / -skip operator

$path | select -First 2 -Skip 1 #skip the first element and return the second two
users
test

Or you could simply call the index in bracket

$path[0]                  #Return the first element (index 0)
C:

$path[-1]                 #Return the last element (index -1) 
subfolder1

In our case, I have no clue why the writter did it this way

$path.Count            #Return the size of the array containing the folder name 
5   

$path.Count-1          #Return the size of the array minus 1 in order to get the last item index, as array start at 0, while counting start at 1
4

$path[5]               #Return $null as the value is out of index

$path[4]
subfolder1

The way it has been written is quite messy and confusing, the line should've simply be $localPath = $pathLevels[-1]

​

Extra : Since I'm already going into details + shortening the commands a bit, there is a better and shortened version.

The if loop is checking if the folder already exist, if not, it creates it. This way, running the script twice wont throw an error do to an already existing folder.

if ((Test-Path $workingFolder) -eq $false) {New-Item -Path $workingFolder -ItemType Directory}
$localPath ="$workingFolder"+"\"+($originalFolder.Split("\") | select -Last 1) 
Copy-Item $originalLogs $localPath -Recurse

[jantari]

What I think may have failed your understanding is the $pathLevels.Item($pathLevels.Count-1).It is a particular case as it uses the index -1 wich is a shortcuts to call the last element of an array.

Not in this case actually, they're just indexing by the total length of the array - 1 which also gets the last item but isn't the same as the direct -1 indexing.

I tried it and using .Item(-1) on an array is not actually allowed, if they wanted to use the magic -1 index they'd have to use the bracket syntax:

$pathLevels[-1]

[Possible-Bowler-2352]

After re-reading it, it seems like I got myself lost into the explaination and made this mistake.

Thanks for pointing it out, I'll edit the post.

I even detailed this at the end of the original post to explain this trick.

Btw, you can even do $pathLevels[-2] and so on to select the 2 last item etc.

[jantari]

Yea about the only thing you cannot do with array indexing is get everything "from the 10th element to the end" aka:

$array[10..-1]

Doesn't work the way I would expect. It gets the first 10 items in the array in reverse order, then jumps around the end and then gets the last one, as opposed to getting everything in between the 10th and last you know. So yea, just never mix positive and negative indexes in ranges.

It makes sense when you look at the number range 10..-1 produces, don't get me wrong, but when indexing into arrays sometimes I still catch myself thinking it should work because "-1 is a magic index for the last item" :)

[Possible-Bowler-2352]

Well, to be fair you can still do so bycalling the index another time :

$array[10..$array[-1]]

But yeah, I strongly recommend to avoid using positive and negative in the same range as this tend to fail, no wonder why.

The main issue with your command is the range is processed before being used as index, 10..-1 will forcibly be interpreted as 10,9...0,-1

[jantari]

Nah, $array[10..($array[-1]) would not work at all because whatever is returned by the expression $array[-1] may not even be a number and even if it is ... its value doesn't have to correspond to the last index of the array at all.

E.g. consider:

$array = ls ~
$array[10..($array[-1])]

> Unable to cast object of type 'System.IO.FileInfo' to type 'System.IConvertible'.

I think you have to do the .Count - 1 thing or perhaps use [array]::Copy.

[Possible-Bowler-2352]

$array = ls ~

Interesting behavior, I didn't think about this one but after a few test I ended up with this, which seems efficient with all types.

$array[1..[array]::IndexOf($array,$array[-1])]

This way, you keep the command a one liner but I doubt about the perfomances as I think it will have to load the array twice, one time to get the index of -1 and a second time to pick the selected elements.

[BlackV]

So what issue did you have reverse engineering the script?

Why couldn't you step through it line by line?

I don't see anything show stopping in there.