Answer by DrAl for How to do case insensitive search in Vim

As well as the suggestions for \c and ignorecase, I find the smartcase very useful. If you search for something containing uppercase characters, it will do a case sensitive search; if you search for something purely lowercase, it will do a case insensitive search. You can use \c and \C to override this:

:set ignorecase:set smartcase/copyright      " Case insensitive/Copyright      " Case sensitive/copyright\C    " Case sensitive/Copyright\c    " Case insensitive

See:

:help /\c:help /\C:help 'smartcase'