Windows batch to add prefix to file names, why added twice?

Question

In order to add a simple "hello" prefix to all pdf files in a folder I'm using this batch file:

FOR %%F IN (*.pdf) DO (RENAME "%%F" "hello%%F")

Saved this into a "rename.bat" file and placed it into the folder I need the files to be renamed. Then I just double click on "rename.bat".

This almost works but the 1st file gets the prefix added twice.

Let's say in the folder I have: A.pdf, B.pdf, C.pdf, they get converted into:

• hellohelloA.pdf
• helloB.pdf
• helloC.pdf,

Do you know what's wrong in the batch file?

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I noticed it always does this when files are more than one. It works ok when there is only one file in the folder, but it is not very useful :-).

Answer 1

/f removes the issue of recapturing an existing file:

FOR /f "delims=" %%F IN ('DIR /a-d /b *.pdf')  DO (RENAME "%%F" "hello%%F")