How to convert part of file to lowercase?

Question

Using gVIM on XP

How can I convert the left side of this file to lowercase while keeping right side unchanged?

%s/**what goes here?**/g

CONVERTTOLOWERCASE###Keep CaSe
AAAA###AeiOu
BBBB###qWerTy

Desired Results

converttolowercase###Keep CaSe
aaaa###AeiOu
bbbb###qWerTy

Answer 1

Here is the command you are looking for:

%s/^[^#]\+/\=toupper(submatch(0))/

See:

• :help tolower()
• :help sub-replace-special
• :help sub-replace-expression
• :help submatch()