I'm new to this platform and not sure whether what I'm reporting is a bug or not. But this is the issue I'm encountering. I had a special character(Â) which gave error while using sed. echo $'H\xc3\x82Bnc' | sed -E 's/[A-Z]*/`&`/g' sed: RE error: illegal byte sequence $ locale LANG="" LC_COLLATE="C" LC_CTYPE="UTF-8" LC_MESSAGES="C" LC_MONETARY="C" LC_NUMERIC="C" LC_TIME="C" LC_ALL= Now if I set LC_COLLATE, then the command works. echo $'H\xc3\x82Bnc' | LC_COLLATE="en_US.UTF-8" sed -E 's/[A-Z]*/`&`/g' `HÂB`n``c`` Is LC_COLLATE affecting the character range. Why after LC_COLLATE was set, did the code produce no error of illegal byte sequence? I'm using Mac OS 13.1