How to NOT overwrite existing files

Question

Currently, I'm using Copy-Item and wondering if there's a simple command that will only copy files that don't exist or are new files by date/time. Looked online but everything I see seems to be using -WhatIf command. Also, seen -Recurse being used. I don't fully understand what that command does either. Any ideas?

$From = "E:\Folder\*"
$To = "\\Server\Folder"
Copy-Item -Path $From -Destination $To -Verbose

Answer 1

Again, what you are after is easily accomplished with RoboCopy.exe, and this question has been asked here and many other Q&A sites, multiple times. even here on SU.

Robocopy to copy only new folders and files

As well as on SO

https://stackoverflow.com/questions/23303532/use-robocopy-to-copy-only-changed-files

RC will only copy newer files. Files of the same age will be skipped.
C:\SourceFolder D:\DestinationFolder ABC.dll /XO
robocopy c:\users\valery\documents j:\robocopy /XO /E /MAXAGE:20131030 /XD
Result: A full folders tree is created. Only new files copied.

So, your question is really a duplicate of the above.

Otherwise, you end up having to know and do stuff like the below(and if you are new, as you say, it's not easy to find in a single search or set of searches):

Clear-Host
$Source      = 'D:\Temp\Source'
$Destination = 'D:\Temp\Destination'
Get-ChildItem -Path $Source -Recurse | 
ForEach-Object {
    If (Test-Path -Path "$Destination$($PSItem.Name)")
    {
        Write-Warning -Message "n$($PSItem.Name) already exists in $Destination. Checking timestampn"
    Try
    {
        "Copying file if $($PSItem.Name) is newer"
        Get-ChildItem -Path $Destination -Filter $PSItem.Name | 
        Where-Object LastWriteTime -lt $PSItem.LastWriteTime -ErrorAction Stop
        Copy-Item -Path $PSItem.FullName -Destination $Destination -Verbose -WhatIf

    }
    Catch {$PSItem.Exception.Message}
}
Else
{
    Write-Host "`n$PSItem.Name does not Exist in $Destination`n" -ForegroundColor Cyan
    Copy-Item -Path $PSItem.FullName -Destination $Destination -Verbose -WhatIf
}

}
Results
<#
...
WARNING: 
abc.txt already exists in D:\Temp\Destination. Checking timestamp
...
WARNING: 
LexPointOh.txt already exists in D:\Temp\Destination. Checking timestamp
Copying file if $($PSItem.Name) is newer
-a----         10-Apr-21     00:00              0 LexPointOh.txt
What if: Performing the operation 
"Copy File" on target "Item: D:\Temp\Source\LexPointOh.txt 
Destination: D:\Temp\Destination\LexPointOh.txt".
mytest - Copy.txt.Name does not Exist in D:\Temp\Destination
What if: Performing the operation "Copy File" on target 
"Item: D:\Temp\Source\mytest - Copy.txt 
Destination: D:\Temp\Destination\mytest - Copy.txt".
...
#>

Just remove the -WhatIf for it to do stuff.

So, based on your statement:

I don't fully understand what that command does either.

That being the case; then, what I show above would be more of a challenge. Hence why I pointed you to the help files (training site, Youtube, etc.) in my original post.

The above is just one way to do this. PowerShell provides various ways to do X or Y things. For example, here is another way of doing the same use case.

Clear-Host
$Source      = ($SourceFiles      = Get-ChildItem -Path 'D:\Temp\Source')[0].DirectoryName
$Destination = ($DestinationFiles = Get-ChildItem -Path 'D:\Temp\Destination')[0].DirectoryName
Compare-Object -ReferenceObject $SourceFiles -DifferenceObject $DestinationFiles -IncludeEqual | 
ForEach-Object {
    If ($PSItem.SideIndicator -match '==|=>')
    {
        If (
            Get-ChildItem -Path $Destination -Filter $($PSItem.InputObject.Name) | 
            Where-Object LastWriteTime -LT  $PSItem.InputObject.LastWriteTime
        )

        {
            Write-Warning -Message "n$($PSItem.InputObject) already exists in $Destination. Checking timestampn"

            Copy-Item -Path $PSItem.InputObject.FullName -Destination $Destination -ErrorAction SilentlyContinue -Verbose -WhatIf
        }
    }
    Else
    {
        Write-Host "n$($PSItem.InputObject ) does not Exist in $Destinationn" -ForegroundColor Cyan
        Copy-Item -Path $PSItem.InputObject.FullName  -Destination $Destination -Verbose -WhatIf
    }
}
Results
<#
WARNING: 
abc.txt already exists in D:\Temp\Destination. Checking timestamp
What if: Performing the operation "Copy File" on target "Item: D:\Temp\Source\abc.txt Destination: D:\Temp\Destination\abc.txt".
WARNING: 
LexPointOh.txt already exists in D:\Temp\Destination. Checking timestamp
What if: Performing the operation "Copy File" on target "Item: D:\Temp\Source\LexPointOh.txt Destination: D:\Temp\Destination\LexPointOh.txt".
mytest - Copy.txt does not Exist in D:\Temp\Destination
What if: Performing the operation "Copy File" on target "Item: D:\Temp\Source\mytest - Copy.txt Destination: D:\Temp\Destination\mytest - Copy.txt".
...
#>

Yet, any time you are using comparative logic, you are not looking at simple command, in most cases.

So, use the right tool for the job. Unless this is a homework assignment, don't increase your core workload/Don't reinvent the wheel.

Answer 2

You can make use of the cmdlet Get-ChildItem. Your script should basically have this flow:

1. Check if the file exists on the destination folder
2. If exists, then skip
3. If not exist, then copy

I ran a very crude and simple test on my computer and this should work (remember to modify it to your use-case)

$FROM = "T:\Files\Scripts1\BackItUp.ps1"
$TO = "T:\Files2"
if (Get-ChildItem -Path $TO "BackItUp.ps1") {
    Write-Host "file already exists..skipping"
} else {
    Copy-Item $FROM -Destination $TO
}

Answer 3

From Stack Overflow:

Copy-Item (Join-Path $dir_from "*") $dir_to -Exclude (Get-ChildItem $dir_to)

Link: Why is Copy-Item overwriting destination files by default?