Batch file to replace file extensions

Previously I have written how to change extensions of several files by using the command prompt in just a few steps. Now we will see another method for that purpose.

Suppose you want to change all files in a folder with bmp extensions to have them rar extensions instead.

Open Notepad and write:

ren *.bmp *.rar

save this file as renamer.bat

*.bmp is your default extension, *.rar is your preferred extension.
This bat file will rename all *.bmp extension files in the folder to *.rar extension files.