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Asked: 2026-05-27T15:39:55+00:00

I’ve done very little with batch files but I’m trying to track down a

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I’ve done very little with batch files but I’m trying to track down a strange bug I’ve been encountering on a legacy system.

I have a number of .exe files in particular folder. This script is supposed to duplicate them with a different file name.

Code From Batch File

for %%i in (*.exe) do copy \\networkpath\folder\%%i \\networkpath\folder\%%i.backup.exe

(Note: The source and destination folders are THE SAME)

Example Of Desired Behavior:

File1.exe -->  Becomes -->  File1.exe.backup.exe
File2.exe -->  Becomes -->  File2.exe.backup.exe

Now first, let me say that this is not the approach I would take. I know there are other (potentially more straight forward) ways to do this. I also know that you might wonder WHY on earth we care about creating a FileX.exe.backup.exe. But this script has been running for years and I’m told the problem only started recently. I’m trying to pinpoint the problem, not rewrite the code (even if it would be trivial).

Example Buggy Output:

File1.exe.backup.exe
File1.exe.backup.exe.backup.exe
File1.exe.backup.exe.backup.exe.backup.exe
File1.exe.backup.exe.backup.exe.backup.exe.backup.exe
File1.exe.backup.exe.backup.exe.backup.exe.backup.exe.backup.exe
File1.exe.backup.exe.backup.exe.backup.exe.backup.exe.backup.exe.backup.exe
etc...
File2.exe.backup.exe
File2.exe.backup.exe.backup.exe
File2.exe.backup.exe.backup.exe.backup.exe
File2.exe.backup.exe.backup.exe.backup.exe.backup.exe
File2.exe.backup.exe.backup.exe.backup.exe.backup.exe.backup.exe
File2.exe.backup.exe.backup.exe.backup.exe.backup.exe.backup.exe.backup.exe

Not knowing anything about batch files, I looked at this and figured that the condition of the for statement was being re-evaluated after each iteration – creating a (near) infinite loop of copying (I can see that, eventually, the copy will fail when the names get too long).

This would explain the behaviour I’m seeing. And when cleaned the directory in question so that it had only the original File1.exe file and ran the script it produced the bug code. The problem is that I CANNOT replicate the behaviour anywhere else!?!

When I create a folder locally with a few .exe files and run the script – I get the expected output. And yes, if I run it again, I get one instance of ‘File1.exe.backup.exe.backup.exe’ (and each time I run it again, it increases in length by one). But I cannot get it to enter the near-infinite loop case.

It’s been driving me crazy.

The bug is occurring on a networked location – so I’ve tried to recreate it on one – but again, no success. Because it’s a shared network location, I wondered if it could have something to do with other people accessing or modifying files in the folder and even introduced delays and wrote a tiny program to perform actions in the same folder – but without any success.

The documentation I can find on the ‘for’ statement doesn’t really help, but all of the tests I’ve run seem to suggest that the in (*.exe) section is only evaluated once at the beginning of execution.

Does anyone have any suggestions for what might be going on here?

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1 Answer

  1. Editorial Team

    I agree with Andriy M’s comment – it looks to be related to Windows 7 Batch Script 'For' Command Error/Bug

    The following change should fix the problem:

    for /f "eol=: delims=" %%i in ('dir /b *.exe') do copy \\networkpath\folder\%%i \\networkpath\folder\%%i.backup.exe

    Any file that starts with a semicolon (highly unlikely, but it can happen) would be skipped with the default EOL of semicolon. To be safe you should set EOL to some character that could never start a file name (or any path). That is why I chose the colon – it cannot appear in a folder or file name, and can only appear after a drive letter. So it should always be safe.

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