sed ignoring case for search but respecting case for subtitute

Shell Programming and Scripting
1

Hi
I want to make string substitution ignoring case for search but respecting case for subtitute. Ex changing all occurences of "original" in a file to "substitute":
original becomes substitute
Origninal becomes Substitute
ORIGINAL becomes SUBSTITUTE

I know this a little special but it's not the first time I need such a function and did not find a simple sed or awk flag for that.

Thanks for your help

2

There is no sed flag to do such a substitution. You just have to do three search and substitute operations.