Remove all permissions to a file, except the owner of the file - powershell

Question

I would like to do something similar to How to Remove all permissions for a specific user?, but I want to remove all access to the file for everybody except the owner of the file.
Is it possible to do that in a relatively clean way?
I suppose I could call get-acl C:\users\myusername\AppData\Local\Temp\TheFile.txt and then walk through all the users listed there, and remove all rights for each one (as described in the linked question above), but is there an easier way?

Answer 1

Examplecode in a function (Put it simply in the same Scriptfile, above all your own code):
function Remove-ACLEntries
{
[CmdletBinding()]
param(
[string]$File
)
$authusers = ((New-Object System.Security.Principal.SecurityIdentifier 'S-1-5-11').Translate([System.Security.Principal.NTAccount])).Value
$acl = Get-Acl $File
$acl.SetAccessRuleProtection($True, $False)
$owner = $acl.owner;
For($i=$acl.Access.Count - 1; $i -gt 0; $i--)
{
$rule = $acl.Access[$i]
if ($rule.IdentityReference -ne $owner -or $rule.IdentityReference -eq $authusers)
{
$acl.RemoveAccessRule($rule)
}
}
Set-ACL -Path $file -AclObject $acl | Out-Null
}
Usage Single File:
Remove-ACLEntries -File c:\your\path\to\file.txt
Usage Multiple Files:
$files = Get-Childitem c:\your\path -Recurse
foreach ($file in $files){ Remove-ACLEntries -File $file.Fullname }
Attention: The User you are using to operate this function must have fullaccess to the file by himself. If the function don't working, try to run the powershell in Adminmode.
Greetings, Ronny

Answer 2

The example below removes all the ACLs and sets the ACL to allow Full Control for the owner of the file.
$acl = Get-Acl "$filePath"
$object = New-Object System.Security.Principal.Ntaccount($acl.owner)
$AccessRule = New-Object System.Security.AccessControl.FileSystemAccessRule($acl.owner,"FullControl","Allow")
$acl.SetOwner($object)
$acl.SetAccessRuleProtection($true,$false)
$acl.SetAccessRule($AccessRule)
#$acl.SetAccessRule($sysUserAccessRule)
$acl | Set-Acl "$filePath"