Use “<strong>\c</strong>” anywhere in a search to ignore case (overriding your ignorecase or smartcase settings).
e.g. “<strong>/\cfoo</strong>” or “<strong>/foo\c</strong>” will match foo, Foo, fOO, FOO, etc.
Use “<strong>\C</strong>” anywhere in a search to force case matching.
e.g. “<strong>/\Cfoo</strong>” or “<strong>/foo\C</strong>” will only match foo.
You can set vim to ignore case on all your searches by running “<strong>:set ignorecase</strong>”.
If “<strong>ignorecase</strong>” is on, you can vim to ignore case on searches of only lowercase letters by running “<strong>:set smartcase</strong>”. (Searches with any capitalization or with “<strong>\C</strong>” will run a case-sensitive search.)
from Vim’s <strong>:help ignorecase</strong> and <strong>:help smartcase</strong>