renaming multiple file extension in debian and windows 7

self note to rename multiple file extensions

debian

rename 's/\.(original extension)$/\.(new extension)/' *.(original extension)

windows 7

ren *.(original extension) *.(new extension)

*note : if u end up with redundant file extensions, remove them with

ren *.(original extension) *.

 also can be used for renaming multiple files, but right now i just want to rename the extension