Ah, OK, thanks, I see what you're saying now. Clearly grep does not behave the way you're asking for. I don't think POSIX requires that behavior either. The relevant part of POSIX says that for -i
not only the character, but also its case counterpart (if any), shall be matched http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_02 which indicates that the POSIX folks did not consider examples such as Greek sigma, where a single letter can have multiple case counterparts. Even if POSIX doesn't specify the behavior, it might be nice for GNU grep to do it anyway, if someone could take the time to implement it without undue performance loss. You're welcome to file a bug report on the Savannah bug tracker about this. <http://savannah.gnu.org/bugs/?group=grep>
