Windows batch file loop running one extra iteratio

Question

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• At which point does `for` or `for /R` enumerate the directory (tree)? 1 answer

I'm using a windows batch file to rename a very large number of files in one go. The renaming simply adds a prefix to the file name. The file executes fine except for the last file, to which the prefix is somehow applied twice. I'm not sure what I'm doing wrong. Can anyone point out the problem to me?

for %%i in (*.csv) do ren %%i myprefix_%%i

Answer 1

@echo off
SETLOCAL
DEL *.csv
XCOPY ..\*.csv .
(
for %%i in (*.csv) do (
echo ====================
echo %%i
dir *.csv
ren %%i x%%i
dir *.csv
echo ====================

)
)>u:\junk.txt&edit u:\junk.txt

I ran the above batch in a clean directory below a directory that contained a few .CSVs. All it does is zap the current directory's .csvs, copy those from the parent directory and then rename by prefixing. It revealed quite a bit.

(U: is a RAMDRIVE, EDIT executes EDITPLUS; NOTEPAD would do as well here)

The operation depends on quite what prefix is added. A prefix starting "a" works differently from a prefix starting "x". AND the result depends on the filesystem being used. NTFS presents the filenames alphabetically but the FAT system on the RAMDRIVE doesn't sort the names.

I believe the problem is caused by the 'findnext' filename mechanism not dealing as expected with a changing list of filenames. As it changes one, that name may move in the list and hence the file may be reprocessed as its new name is encountered again - possibly multiple times.

A cure is to replace the for selection with

for /f "delims=" %%i in ('dir /b *.csv') do (

where the DIR list is created and THEN processed, so the changes don't affect it.

Answer 2

You may be having some spaces in your filenames. Use double-quotes around filenames. Try the following:

for %%i in (*.csv) do ren "%%I" "myprefix_%%I"

This will execute as:

ren "tmp - Copy.csv" "myprefix_tmp - Copy.csv"

Also, you should look for any hidden files.