Tab completion in minibuffer: case insensitive

Question

When the minibuffer offers tab completion, how can I make that case-insensitive?

Preferably a global setting that makes any completion – a filename, a command, ido, etc. – obey that setting.

Answer 1

Sure. Set variable completion-ignore-case to t. Put this in your init file:

(setq completion-ignore-case  t)

C-h v completion-ignore-case:

completion-ignore-case is a variable defined in C source code.

Its value is nil

Documentation:

Non-nil means don't consider case significant in completion.

For file-name completion, read-file-name-completion-ignore-case controls the behavior, rather than this variable.

For buffer name completion, read-buffer-completion-ignore-case controls the behavior, rather than this variable.

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Note that this is not a user option, and so is excluded from Customize. You can set it but you cannot set it using Customize. The most common use of it is to bind it (not assign it) in a given command. But nothing prevents you from assigning it, to affect the general behavior.