How do I edit or modify an existing Vim macro programmatically without re-recording it?

Explanation

Vim macros are stored as plain text in registers, which means you can inspect and modify them like any other string. Instead of re-recording an entire macro just to fix a small typo or swap one command for another, you can rewrite the register directly using :let and Vimscript's substitute() function.

How it works

• :let @q = ... assigns a new value to register q (where the macro lives)
• substitute(@q, 'old', 'new', 'g') runs a search-and-replace on the current macro string
• You can inspect the raw macro content first with :echo @q or :reg q

Example

You recorded a macro that inserts foo, but you want it to insert bar instead:

" Inspect what the macro currently contains
:echo @q

" Fix the typo without re-recording
:let @q = substitute(@q, 'foo', 'bar', 'g')

To concatenate two macros into one — run what @a does, then what @b does:

:let @q = @a . @b

To strip an accidentally recorded trailing <Esc> from the end of a macro:

:let @q = substitute(@q, '\e$', '', '')

Tips

• For more complex edits, paste the macro into a scratch buffer ("qp), edit it as text, then yank it back ("qy$) to reload the register
• Use :execute 'normal @q' to test the modified macro immediately after editing
• This approach works for any register, making it useful to build composite macros by combining existing ones