How do I programmatically extend or modify a recorded macro without re-recording it?

Explanation

Vim stores macros as plain text in registers — the same registers used for yanked text. This means you can read, concatenate, and rewrite macro content using :let, giving you surgical control over recorded sequences without re-recording from scratch.

How it works

• @a in a Vimscript expression reads the current content of register a
• The . operator concatenates strings
• Double-quoted strings like "\<CR>" represent special keys (the backslash notation is resolved to the actual control character)
• Assigning back to @a updates the macro register immediately

Example

You recorded a macro in @q but forgot to add a j to advance to the next line at the end:

:let @q = @q . "j"

Append a newline + some text at the end of each processed line:

:let @q = @q . "A;\<Esc>j"

Prepend a step to move to the beginning of the line first:

:let @q = "^" . @q

Tips

• Use "\<Esc>", "\<CR>", "\<C-w>", etc. for special keys inside double-quoted strings
• To inspect the current macro content: :echo @q (shows the raw keystroke string)
• Combine with :put a to paste the macro into a buffer for visual editing, then yank it back with "ayy
• You can store permanent macros in your vimrc: let @q = '...' so they survive restarts