PowerShell script not zipping correct files

Question

 Function Zip
{
    Param
    (
        [string]$zipFile
        ,
        [string[]]$toBeZipped
    )
    $CurDir = Get-Location
    Set-Location "C:\Program Files\7-Zip"
    .\7z.exe A -tzip $zipFile $toBeZipped | Out-Null
    Set-Location $CurDir
}
$Now = Get-Date
$Days = "60"
$TargetFolder = "C:\users\Admin\Downloads\*.*"
$LastWrite = $Now.AddDays(-$Days)
$Files = Get-Childitem $TargetFolder -Recurse | Where {$_.LastWriteTime -le "$LastWrite"}
$Files
Zip C:\Users\Admin\Desktop\TEST.zip $Files

I am testing out this script I found online. My problem is that instead of zipping the files in the target folder, it is copying and zipping the contents of the 7-zip program file folder. What could cause this? Thanks in advance

Philologian

Where did you find the script? When file objects are forced to strings they just become the file names... not the full path. I think you need to process each file 1 by 1. Also you could remove Out-Null to help get yourself more information as to what is happening. – Flow

@Matt: Here they indeed stringify to file names only, which is the problem, but whether they stringify to mere file names or full paths generally depends on the specifics of the Get-ChildItem call, (very) unfortunately - I've tried to summarize the rules in my answer. – Alben

I saw that. Colour me impressed. It annoys me that it is inconsistent. I'm just used to using fullnames now – Flow

@Matt: Yes, it's very unfortunate behavior that makes for insidious bugs. I'm glad the problem no longer occurs in PS Core (and let's hope that the change, which was technically a breaking one, was intentional or will at least be retained). – Alben

Answer 1

Pass the files as full paths to the Zip function, using their .FullName property (PSv3+ syntax):

Zip C:\Users\Admin\Desktop\TEST.zip $Files.FullName

---

The problem is that, in Windows PowerShell, the [System.IO.FileInfo] instances returned by Get-ChildItem situationally^[1] stringify to their file names only, which is what happened in your case, so your Zip function then interpreted the $toBeZipped values as relative to the current location, which is C:\Program Files\7-Zip at that point.

That said, it's better not to use Set-Location in your function altogether, so that in the event that you do want to pass actual relative paths, they are correctly interpreted as relative to the current location:

Function Zip {
    Param
    (
        [Parameter(Mandatory)] # make sure a value is passed          
        [string]$zipFile
        ,
        [Parameter(Mandatory)] # make sure a value is passed
        [string[]]$toBeZipped
    )
    # Don't change the location, use & to invoke 7z by its full path.
    $null = & "C:\Program Files\7-Zip\7z.exe" A -tzip $zipFile $toBeZipped
    # You may want to add error handling here.
}

---

[1] When Get-ChildItem output stringifies to file names only:

Note:

• If Get-ChildItem output is to be passed to other file-processing cmdlets, say Rename-Item, the problem can be bypassed by providing input to them via the pipeline, which implicitly binds to the target cmdlet's -LiteralPath parameter by full path - see this answer for more information.

• The related Get-Item cmdlet output always stringifies to the full path, fortunately.

• In PowerShell (Core) v6.1+, Get-ChildItem too always stringifies to the full path, fortunately.

The following therefore only applies to Get-ChildItem in Windows PowerShell:

The problem is twofold:

• Even PowerShell's built-in cmdlets bind file / directory arguments (parameter values - as opposed to input via the pipeline) not as objects, but as strings (changing this behavior is being discussed in GitHub issue #6057).

• Therefore, for robust argument-passing, you need to ensure that your Get-ChildItem output consistently stringifies to full paths, which Get-ChildItem does not guarantee - and it's easy to forget when name-only stringification occurs or even that you need to pay attention to it at all.

Always passing the .FullName property values instead is the simplest workaround or, for reliable operation with any PowerShell provider, not just the filesystem, .PSPath.

[System.IO.FileInfo] and [System.IO.DirectoryInfo] instances output by a Get-ChildItem command stringify to their file names only, if and only if:

• If one or more literal directory paths are passed to -LiteralPath or -Path (possibly as the 1st positional argument) or no path at all is passed (target the current location); that is, if the contents of directories are enumerated.

• and does not also use the -Include / -Exclude parameters (whether -Filter is used makes no difference).

• By contrast, whether or not the following are also present makes no difference:

  • -Filter (optionally as the 2nd positional argument, but note that specifying a wildcard expression such as *.txt as the 1st (and possibly only) positional argument binds to the -Path parameter)
  • -Recurse (by itself, but note that it is often combined with -Include / -Exclude)

Example commands:

# NAME-ONLY stringification:

Get-ChildItem | % ToString # no target path

Get-ChildItem . | % ToString # path is literal dir.

Get-ChildItem . *.txt | % ToString  # path is literal dir., combined with -Filter

# FULL PATH stringification:

Get-ChildItem foo* | % ToString # non-literal path (wildcard)

Get-ChildItem -Recurse -Include *.txt | % ToString # use of -Include

Get-ChildItem file.txt | % ToString # *file* path

Alben

Extensive explanation. I am surprised that Get-ChildItem -Recurse -Include *.txt | % ToString produces the current directory files, but Get-ChildItem -Include *.txt | % ToString does not. – Rivas

@lit: That is indeed another pitfall - see github.com/PowerShell/PowerShell/issues/3304 – Alben

Answer 2

If you (temporarily) disable the |Out-Null you'll see what error msg pass along.
$Files contains objects not just an array of file names.

By default powershell tries to stringify this using the Name property which doesn't contain the path - so 7zip can't find the files as you also change the path to the 7zip folder (and -recurse collecting $files)

So change the line

$Files = Get-Childitem $TargetFolder -Recurse | Where {$_.LastWriteTime -le "$LastWrite"}

and append

| Select-Object -ExpandProperty FullName

A slightly reformatted verson ofyour source:

Function Zip{
    Param (
        [string]$zipFile,
        [string[]]$toBeZipped
    )
    & "C:\Program Files\7-Zip\7z.exe" A -tzip $zipFile $toBeZipped | Out-Null
}
$Days = "60"
$LastWrite = (Get-Date).Date.AddDays(-$Days)

$TargetFolder = "$($ENV:USERPROFILE)\Downloads\*"

$Files = Get-Childitem $TargetFolder -Recurse | 
   Where {$_.LastWriteTime -le $LastWrite} | 
     Select-Object -ExpandProperty FullName
$Files
Zip "$($ENV:USERPROFILE)\Desktop\TEST.zip" $Files

Illeetvilaine

Ok. It worked. However if I try it again, and there isn't any folders that meet the criteria to be zipped, it will zip the contents of the 7zip program. Is there anyway to prevent that? – Philologian

Sorry I can't follow I just tested my posted version with the suggest edits and it run's here without flaw. I agree with mklement0 that it's better NOT to change the path to 7zip folder to avid zipping that folder as suggested by @Alben – Illeetvilaine

Yes, the posted version works. However, lets say I run this in a file that doesn't have any files to be zipped, what will happen is that all of the contents of the 7-zip program are copied into the ZIP folder. – Philologian

Make the params mandatory Param ( [Parameter(Position=0,mandatory=$true)] [string]$zipFile, [Parameter(Position=1,mandatory=$true)] [string[]]$toBeZipped ) – Illeetvilaine

@LotPings: Here the objects indeed stringify to file names only, which is the problem, but whether they stringify to mere file names (.Name) or full paths (.FullName) generally depends on the specifics of the Get-ChildItem call, (very) unfortunately - I've tried to summarize the rules in my answer. – Alben