How do I make Vim's command-line tab completion case-insensitive for file and buffer names?

Explanation

:set wildignorecase makes Vim's command-line tab completion treat uppercase and lowercase letters as equivalent when completing file names, buffer names, and other identifiers. On case-sensitive filesystems (Linux), this lets you type a partial name in any case and still match the correct target.

How it works

• Affects all wildmenu completions: :edit, :split, :find, :buffer, :cd, :source, and others
• When you type a partial path and press <Tab>, Vim matches regardless of case
• Does not affect pattern searching (ignorecase and smartcase control that)
• Does not change how filenames are stored — it only affects the matching during completion

Example

On a Linux system with a file named README.md:

:e readme<Tab>    → completes to :e README.md
:sp Config<Tab>   → completes to :sp config.py  (or CONFIG.py)
:b Main<Tab>      → matches MainController buffer

Without wildignorecase, these completions would find no matches on a case-sensitive filesystem.

Tips

• Add set wildignorecase to .vimrc to make it permanent
• Combine with set wildmenu and set wildmode=longest:full,full for the best completion experience
• Different from set fileignorecase, which affects how Vim handles filenames internally across all operations
• Particularly useful when working on Linux with codebases that use PascalCase file names