How To Write New Checksums Files To Alternate Location

PowerShell Help
1

I am using the following script to generate a checksum file for hundreds of files in several subdiretories. The files are generated as expected in those directories. However I cannot figure out how to tell the files to be written to a different location that with their original source file. example write the files to c:\checksum\projects.

I know this will be a simple question/answer for someone that uses powershell daily.

 

$files = Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5”

Foreach ($file in $files)
{
$hash = (Get-FileHash -Path $file.fullname -Algorithm SHA256).hash
Add-Content -Path ($file.fullname + ‘.checksum’) -Value $hash
}

 

2

Are you wanting all the files in the same folder or are you wanting to also have their original directory structure under c:\checksum\projects?

This will dump all the checksum files in the c:\Checksum\Projects directory, so beware of name collisions.

$files = Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5”
$dest = "c:\checksum\projects"

Foreach ($file in $files)
{
    $hash = (Get-FileHash -Path $file.fullname -Algorithm SHA256).hash
    $fulldest = Join-Path $dest ($file.name + '.checksum')
    Add-Content -Path $fulldest -Value $hash
}

The previous example uses a foreach statement construct which will load everything into memory. It’s very fast, but if you have a large amount of files this could be an issue. The following example changes it to utilize the pipeline.

$files = Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5”
$dest = "c:\checksum\projects"

$files | ForEach-Object {

    $fulldest = Join-Path $dest ($_.name + '.checksum')
    (Get-FileHash -Path $_.fullname -Algorithm SHA256).hash | Add-Content -Path $fulldest

}

I hope this helps

3

Are you wanting all the files in the same folder or are you wanting to also have their original directory structure under c:\checksum\projects?

This will dump all the checksum files in the c:\Checksum\Projects directory, so beware of name collisions.

$files = Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5”
$dest = "c:\checksum\projects"

Foreach ($file in $files)
{
    $hash = (Get-FileHash -Path $file.fullname -Algorithm SHA256).hash
    $fulldest = Join-Path $dest ($file.name + '.checksum')
    Add-Content -Path $fulldest -Value $hash
}

The previous example uses a foreach statement construct which will load everything into memory. It’s very fast, but if you have a large amount of files this could be an issue. The following example changes it to utilize the pipeline.

$files = Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5”
$dest = "c:\checksum\projects"

$files | ForEach-Object {

    $fulldest = Join-Path $dest ($_.name + '.checksum')
    (Get-FileHash -Path $_.fullname -Algorithm SHA256).hash | Add-Content -Path $fulldest

}

or even

$dest = "c:\checksum\projects"

Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5” | ForEach-Object {

    $fulldest = Join-Path $dest ($_.name + '.checksum')
    (Get-FileHash -Path $_.fullname -Algorithm SHA256).hash | Add-Content -Path $fulldest

}

I hope this helps

4

Actually I should have specified that originally. The same directory structure to avoid the issue of collisions.

5

It’s not pretty, and I’m sure there are better ways to do it, but this works assuming the targets are on the C: drive. If not, replace C: with the appropriate letter.

$files = Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5”
$dest = "c:\checksum\projects"

Foreach ($file in $files)
{
    $path = ($file.fullname | split-path -Parent) -replace 'C:',''
    $newpath = join-path $dest $path
    $fulldest = Join-Path $newpath ($file.name + '.checksum')
    $hash = (Get-FileHash -Path $file.fullname -Algorithm SHA256).hash
    Add-Content -Path $fulldest -Value $hash
}

or

$files = Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5”
$dest = "c:\checksum\projects"

$files | ForEach-Object {

    $path = ($_.fullname | split-path -Parent) -replace 'C:',''
    $newpath = join-path $dest $path
    if(-not (test-path $newpath)){New-Item -Path $newpath -ItemType Directory | Out-Null}
    $fulldest = Join-Path $newpath ($_.name + '.checksum')
    (Get-FileHash -Path $_.fullname -Algorithm SHA256).hash | Add-Content -Path $fulldest

}
6

FANTASTIC! The last example works as I needed. I really appreciate it.

One last question. Is there a way to set the date/time of the newly created checksum file to the same date/time of the original file it was created from?

7

I bet there is. Check this out and see what you can come up with. If you hit a snag after giving it a shot, let us know.

8

Thanks for all of the help.

One least question. I have everything figured out except for one item. Can you provide me an example of how to skip writing the .checksum file if it already exists?

9

You don’t need to check that the file matches a specific criteria or is a certain age? If not, then we can test-path like we did for the folder and only if it’s not found would we calculate the hash and write it.

$files = Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5”
$dest = "c:\checksum\projects"

Foreach ($file in $files)
{
    $path = ($file.fullname | split-path -Parent) -replace 'C:',''
    $newpath = join-path $dest $path
    if(-not (test-path $newpath)){New-Item -Path $newpath -ItemType Directory | Out-Null}
    $fulldest = Join-Path $newpath ($file.name + '.checksum')
    if(-not(Test-Path $fulldest))
    {
        $hash = (Get-FileHash -Path $file.fullname -Algorithm SHA256).hash
        Add-Content -Path $fulldest -Value $hash
    }
}

or

$files = Get-childitem -Path c:\projects -recurse -include * -Exclude “*.md5”
$dest = "c:\checksum\projects"

$files | ForEach-Object {

    $path = ($_.fullname | split-path -Parent) -replace 'C:',''
    $newpath = join-path $dest $path
    if(-not (test-path $newpath)){New-Item -Path $newpath -ItemType Directory | Out-Null}
    $fulldest = Join-Path $newpath ($_.name + '.checksum')
    if(-not(Test-Path $fulldest))
    {
        (Get-FileHash -Path $_.fullname -Algorithm SHA256).hash | Add-Content -Path $fulldest
    }
}
10

I was over complicating it. Thank you for the quick response. Works perfectly!