Vi editor: "~" is used to change the case of the selected character.

In the vi editor, the tilde (~) key is used to change the case of the character under the cursor. When you press ~ on a lowercase letter, it becomes uppercase, and vice versa. This is a useful command for quickly changing text case without entering insert mode. The command affects only the character directly under the cursor position and moves the cursor to the next character, allowing you to apply it repeatedly.