I'm comming from testing this sample code here: https://devblogs.microsoft.com/scripting/use-powershell-to-compare-two-files/

I'm writing a script i need to copy a large DB-Backup-File (>120GB) from a local Network drive to my local drive for some processing. - The thing is: The file doesn't change very ofthen. (its a Backup of one of our customers who occasionally updates it.) So i want to skip the whole "copy-process" in case it didn't change.

Now, the problem with the skript in the blog is: it still takes about as much time as copying the file without checking. I assume thats because PS needs to load the whole file to generate the hash, but I'm not sure.

anyway: I'm looking for performant alternatives. Things like "just compare the filesize" (would that still work if you rename the file? - it's should, shouldn't it?) or something else in that direction.

p.s. the whole environment is on Windows. In case that matters.

p.p.s. here is a copy of the code I tested. So you don't have to search the Blog for it:

$fileA = "C:\fso\myfile.txt"

$fileB = "C:\fso\CopyOfmyfile.txt"

$fileC = "C:\fso\changedMyFile.txt"

if((Get-FileHash $fileA).hash  -ne (Get-FileHash $fileC).hash)

 {"files are different"}

Else {"Files are the same"}

CodePudding user response：

I believe that your problem is due to the fact that the calculation of the hash of the file needs to run through the whole file.

Therefore you might opt for another thing to verify, like for example the last modification date of a file which, in Powershell, can be calculated as follows:

(Get-Item "C:\fso\myfile.txt").LastWriteTime