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I recovered about 300 MKV files from a 4TB HDD, using Photorec. Those files are named according to their first sector, for instance "f123456789.mkv". Now, I want to rename them all by adding their corresponding begining and ending offset values, like this : "[63209875968-70209875967] f123456789.mkv" (for a file size of 7000000000 bytes in this example). I tried this batch script :

for %%F in (f*.mkv) do (
    SET name=%%~nF
    SET sectors=%name:~1%
    SET /a offset1=%sectors%*512
    SET /a offset2=%offset1%+%%~zF-1
    RENAME "%%F" "[%offset1%-%offset1%] %%F"
)

But it doesn't work, although the individual commands do work within CMD ; the variables are not expanded correctly. I tried with "setlocal enabledelayedexpansion", and !variable! instead of %variable%, to no avail. Besides, I read that the calculations in CMD were limited to a 32-bit accuracy, so if I get it right, using batch command set /a I could only calculate offsets up to 4294967296 anyway (even for the first file that's not enough). Which means I should use another scripting language, but which one would be appropriate, and how could I quickly find the corresponding command to do what I want to do ? I spent most of the afternoon trying to get the basics of PowerShell and adapt the above script, but so far I was only able to print the filenames and remove the first character... (It's quite frustrating, considering that with the same amount of time I could have done this task manually and it may be finished by now ! It's more prone to error though, another reason why I'd like to automate it...) I just need to :

  • set a variable with the first sector number, obtained from the file name,
  • set a variable for the first offset value, which is the sector number multiplied by 512,
  • set a variable for the last offset value, which is the first offset plus the file size minus 1,
  • rename the files using the aforementioned pattern.

Any idea ? Thanks !


update 1

So, after another night of clumsy fiddling with Powershell, I think I got a few things right. The first steps seem to work fine, but I get undecipherable error after undecipherable error when it comes to actually renaming the files. What is wrong with the Rename-Item command below ? And are there ways to do this more simply / elegantly ?

foreach ($file in gci *.mkv) {
  $sectors = [string]($file.BaseName).substring(1)
  $offset1 = [int64]$sectors * 512
  $offset2 = [int64]$offset1 + [int64]($file.Length) - 1
  Rename-Item -NewName {"[$offset1-$offset2]" $file}
}

update 2

I solved this by correcting the last line like this :

Rename-Item $file -NewName ( "[$offset1-$offset2] " + $file.name )
  • For future questions, include the error output to help others troubleshoot with you. – root Oct 17 '16 at 13:35
  • @root The error codes were in french, hence why I did not include them. – GabrielB Nov 9 '16 at 17:41
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The ForEach loop you posted looks correct in that it achieves your goals, all but the Rename-Item line. It should be:

Rename-Item $file -NewName $offset1"-"$offset2".mkv"

To find more info on a cmdlet and its syntax, use Get-Help Remove-Item -full. You'll find extended details along with helpful examples.

  • I solved it on my own, but indeed the "$file" component was missing in the last line. I tried to read the included help each time I was stuck but it was barely helpful most of the time, it seems to assume that the user already has a certain knowledge level and rarely provide ways to fix common errors. – GabrielB Nov 9 '16 at 17:58

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