How to make sed case insensitive

Shell Programming and Scripting
1

I need to remove a pattern say, ABCD whether it is in uppercase or lowercase from a string. How to do it using SED?
for example
ABCDEF should output to EF
abcdEF should also output to EF

2

Hi,

sed 's/ABCD//i' file

Should do it.

HTH Chris

3

sed 's/[Aa][Bb][Cc][Dd]\(..\)/\1/' file