How do I make a single search case-insensitive without changing my global ignorecase setting?

Explanation

Vim's \c and \C atoms let you override the global ignorecase and smartcase settings on a per-search basis. Adding \c anywhere in a pattern forces case-insensitive matching for that search only, while \C forces case-sensitive matching.

How it works

• \c — makes the entire pattern case-insensitive, regardless of ignorecase/smartcase
• \C — makes the entire pattern case-sensitive, regardless of ignorecase
• Both atoms affect the whole pattern, no matter where they appear

Example

With set ignorecase smartcase active (case-sensitive when uppercase is present):

/Error        ← case-sensitive (uppercase E triggers smartcase)
/Error\c      ← case-insensitive: finds "error", "ERROR", "Error"

With set noignorecase:

/error        ← case-sensitive by default
/error\c      ← overrides: finds "error", "Error", "ERROR"
/Error\C      ← forces case-sensitive even if ignorecase is on

You can place \c or \C at the start, end, or anywhere in the pattern — they always apply to the full search.

Tips

• Use \c when you know you want a case-insensitive one-off search without reconfiguring settings
• Use \C in patterns used in scripts or autocommands where you need guaranteed case-sensitive behavior regardless of user config
• Works in substitutions too: :%s/pattern\c/replacement/g