How do I open the command-line window while I am already typing a command?

Explanation

Pressing <C-f> while in the command-line (:, /, or ? prompt) opens the command-line window with your partially-typed command already loaded and ready for full Vim editing. This is the mid-typing equivalent of q: (or q/) from Normal mode.

How it works

• You start typing a complex command, e.g. :%s/foo/bar/
• You realize you want to use Vim motions to edit it more carefully
• Press <C-f> — a new window opens containing the command-line history, with your in-progress command at the bottom
• Edit it with the full power of Vim (motions, operators, registers)
• Press <CR> on the line you want to execute, or :q to cancel

Example

Typing: :%s/very-long-pattern-you-misspelled/
↓ press <C-f>

Opens the command-line window with:
  :%s/very-long-pattern-you-misspelled/

You can now use F- to jump to the hyphen, cw to fix the typo, and <CR> to run it.

Tips

• <C-f> from / or ? mode opens the search history window instead
• q: opens the command-line window from Normal mode (history only, no in-progress command)
• :q or <C-c> closes the command-line window without executing